BACTERIA IN OTHER FOODS
Shell-fish have recently claimed the attention of bacteriologists, owing to the outbreak of typhoid and other epidemics apparently traceable to oysters.
It is four or five years since Professor Conn startled the medical world by tracing an epidemic of typhoid fever to the consumption of some uncooked oysters.[71] Almost at the same time Sir William Broadbent published in the British Medical Journal a series of cases occurring in his practice which illustrated the same channel of infection. Since then a number of similar items of evidence to the same effect have cropped up. Hence there is little wonder that a number of investigators concentrated their attention upon this matter. Professors Herdman and Boyce, of Liverpool, Dr. Cartwright Wood, Dr. Klein, and Dr. Timbrell Bulstrode are some of the chief contributors to the elucidation of this problem.
The mode of infection of oysters by pathogenic bacteria is briefly as follows: The sewage of certain coast towns is passed untreated out to sea. At or near the outfall, oyster-beds are laid down for the purpose of fattening oysters. Thus they become contaminated with saprophytic and pathogenic germs contained in the sewage. It will be at once apparent that several preliminary questions require attention before any deductions can be drawn as to whether or not oysters convey virulent disease to consumers. To the solution of these Dr. Cartwright Wood was one of the first to address himself.
The precise conditions which render one locality more favourable than another in respect to oyster culture are not fully known. But it has been observed that they do not flourish in water containing less than three per cent. of salt. Hence they are absent from the Baltic Sea, which, owing to the fresh water flowing into it in rivers, contains a smaller percentage of salt than three. Oysters appear in addition, to favour a locality where they find their chosen food of small animalculæ and particles of organic matter. Such a favourable locality is the mouth of a river, where tides and currents also assist in bringing food to the oyster. Unfortunately, however, in a crowded country like England such localities round her coasts are frequently contaminated by sewage from outfalls. Thus the oysters and the sewage come into intimate relation with each other.
Professor Giaxa carried out some experiments in 1889 at Naples which appeared to show that the bacilli of cholera and typhoid rapidly disappeared in ordinary sea-water. Other observers at about the same time, notably Foster and Freitag, arrived at an opposite conclusion. In 1894 Professor Percy Frankland, in a report to the Royal Society, declared "that common salt, whilst enormously stimulating the multiplication of many forms of water bacteria, exerts a directly and highly prejudicial effect on the typhoid bacilli, causing their rapid disappearance from the water, whether water bacteria are present or not." It was at this time, when the matter was admittedly in an unsatisfactory stage, that Dr. Cartwright Wood made his experiments.[72] We have not space here to enter into this work. But his conclusions seem to have been amply established, and were to the effect that typhoid and cholera bacilli could, as a matter of fact, exist over very lengthened periods in ordinary sea-water. The next step was to demonstrate the length of time the bacilli of cholera remained alive in the pallial cavity and body of the oyster. Dr. Wood found they did so for eighteen days after infection, though in greatly diminished numbers. This diminution was due to one or all of three reasons: (a) the effect of the sea-water already referred to as finally prejudicial to bacilli of typhoid; (b) the vital action of the body-cells of the oyster; (c) the washing away of bacilli by the water circulating through the pallial cavity.
It will have been noticed that up to the present we have learned that typhoid bacilli can and do live in sea-water, and also inside oysters up to eighteen days, but in ever-diminishing quantities. The question now arises: What is the influence of the oyster upon the contained bacilli? Under certain conditions of temperature organisms may multiply with great rapidity inside the shell of the oyster. Yet, on the other hand, the amœboid cells of the oyster, the acid secretion of its digestive glands, or the water circulating through its pallial cavity, may act inimically on the germs. Proof can be produced in favour of the third and last-named mode by which an oyster can cleanse itself of germs. So far, then, we have met with no facts which make it impossible for oysters to contain for a lengthened period the specific bacteria of disease. Let us now turn to their opportunity for acquiring such disease germs. It is afforded them during the process of what is termed "fattening." By this process the body of the oyster acquires a plumpness and weight which enhances its commercial value. This desired condition is obtained by growing the oyster in "brackish" water, for thus it becomes filled out and mechanically distended with water. But if this water contains germs of disease, what better opportunity could such germs have for multiplication than within the body-cavity of an oyster? "The contamination of sea-water, therefore, in the neighbourhood of oyster-beds may undoubtedly lead to the molluscs becoming infected with pathogenic organisms" (Wood). Yet we have seen that, apart altogether from the individual susceptibilities or otherwise of the consumer, there are in the series of events necessary to infection many occasions when circumstances would practically free the oysters from infection.
The sources of pollution of oysters are not the fattening beds alone. The native beds also may afford opportunity for contamination. Thirdly, in packing and transit, and fourthly, in storage in shops and warehouses, there is frequently abundant facility for putrefactive bacteria to gain entrance to the shells of oysters.
Dr. Klein's researches[73] into this question have been wholly confirmatory of the facts elicited by Dr. Cartwright Wood. Despite the tendency of the bacilli of cholera and typhoid to die out quickly in crude sewage, the sewage is sufficiently altered or diluted at the outfall for these organisms to exist there in a virulent state. We may give Dr. Klein's conclusions:
1. That the cholera and typhoid bacilli are difficult of demonstration in sewage known to have received them.
2. Both organisms may persist in sea-water tanks for two or three weeks, the typhoid bacillus retaining its characteristics unimpaired, the cholera bacillus tending to lose them.
3. Oysters from sources free of sewage contained no bacteria of sewage.
4. Oysters from sources exposed to risk of sewage contamination did contain colon bacilli and other sewage bacteria.
5. In one case Eberth's typhoid bacillus was found in the mingled body and liquor of the oyster.
Nor do typhoid bacilli lose activity or virulence by passing through an oyster.
These researches once and for all established the fact that oysters ordinarily grown on oyster-beds contaminated with bacteria may, and do on occasion, contain the virulent specific bacillus of typhoid, which can live both in sea-water and within the shell of the oyster. This being so, it will probably appear to the reader that the risk of infection of typhoid by oysters is very serious indeed. Yet in actual practice many conditions have to be fulfilled. For, in addition to the fact that the oysters must be consumed, as is usual, uncooked, the following conditions must also be present.
(a) Each infective oyster must contain infected sewage, which presupposes that typhoid excreta from patients suffering from the disease have passed into that particular sewage untreated and not disinfected.
(b) The infective oyster must be fed upon infected sewage, and still contain the virus in its substance.
(c) It has to be eaten by a susceptible person.
(d) There must have been no period of natural cleansing after "fattening."
Even to this formidable list of conditions we must add the further remark that, owing to the vitality of the body-cells of the oyster, or to the lessened vitality of the bacilli of cholera and typhoid, it is generally the case that the tendency of these organisms is rather to decrease and die out than live and multiply.
We shall probably maintain a satisfactory balance of truth if we place alongside these facts the summary of the Local Government Board Report.
"There can be no doubt," wrote Sir Richard Thorne, "that oysters which have been brought into sustained relation with the typhoid bacillus are liable to exhibit that microbe within the shell contents and to retain it for a while under circumstances not only permitting its rapid multiplication when transferred again to appropriate media, but conserving at the same time its ability to manifest its hurtful properties."
From what has been said the preventive treatment is obvious. All oyster-layings and shell-fish beds round the coast should be superintended and inspected by the sanitary authority of the Government. The importation of foreign oysters, grown on uncontrolled beds, should, if possible, be restricted or supervised. Further, as a protective measure of the first importance, oysters should be cleansed, after fattening on a contaminated bed, by being deposited for several weeks at some point along the coast which is washed by pure sea-water. Retention in dirty water-tanks, in uncleanly shops and warehouses, is also to be greatly deprecated.
In order to examine oysters bacteriologically, it is necessary to pay particular attention to the water in the pallial cavity, the contents of the alimentary canal, and the washings of the shell itself. Ordinary media may be used for obtaining a growth of the contained organisms.
Other shell-fish than oysters do, from time to time, cause epidemics or individual cases of gastro-intestinal irritation, and probably contain various germs. These they acquire in all probability from their food, which by their own choice is frequently of a doubtful character.
Meat. Parasites are occasionally found in meat, but bacteria are comparatively rare. Not that they do not occur in the bodies of animals used for human consumption, for in the glands, mesenteries, and other organs they are common. But in those portions of the carcass which are used by man, namely the muscles, bacteria are rare. The reasons alleged for this are the acid reaction (sarcolactic acid) and the more or less constant movement during life. A bacterial disease which, perhaps more than any other, might be expected to be conveyed by meat is tubercle. Yet the recent Royal Commission on Tuberculosis has again emphasised the absence of bacilli in the meat substance:
"In tissues which go to form the butcher's joint, the material of tubercle is not often found even where the organs (lungs, liver, spleen, membranes, etc.) exhibit very advanced or generalised tuberculosis; indeed, in muscle and muscle juice it is very seldom that tubercle bacilli are to be met with; perhaps they are somewhat more often to be discovered in bone, or in some small lymphatic gland embedded in intermuscular fat."[74]
The only way in which such meat substance becomes infected with tubercle appears to be through carelessness in the butcher, who perchance smears the meat substance with a knife that has been used in cutting the organs, and so has become contaminated with infected material. Very instructive also are the results at which Dr. Sims Woodhead arrived in compiling evidence for the same Commission on the effect of cooking upon tuberculous meat:
"Ordinary cooking, such as boiling and more especially roasting, though quite sufficient to sterilise the surface, and even the substance for a short distance from the surface of a joint, cannot be relied upon to sterilise tubercular material included in the centre of rolls of meat, especially when these are more than three pounds or four pounds weight. The least reliable method of cooking for this purpose is roasting before a fire; next comes roasting in an oven, and then boiling."[75]
From this statement it will be understood that rolled meat may be a source of infection to a greater degree than the ordinary joint.
Notwithstanding this negative evidence, more than twenty species of bacteria have been isolated from canned meats and hams, and a considerable number of poisoning cases have occurred from meat contaminated with bacteria or their products. The general symptoms of such meat poisoning are vomiting, diarrhœa, fever, and more or less prostration. Ballard and Klein isolated a specific microbe from samples of bacon which appear to have caused an epidemic of infectious pneumonia at Middlesborough. In 1880 occurred the well-known "Welbeck disease" epidemic. A public luncheon was followed by severe and even fatal illness. Seventy-two persons were affected, and four died. A specific bacillus was isolated by Klein. In 1881 much the same thing happened at Nottingham, in which fifteen persons were attacked, and one died. The same bacillus was isolated from the pernicious pork. Again in 1889 an outbreak of diarrhœa at Carlisle was traced to bacterially diseased pork. But taking these and similar cases at their worst, there can be no doubt that under no circumstances is meat as infective as milk.
Ice-cream. In 1894 Dr. Klein had occasion to bacteriologically examine ice-creams sold in the streets of London. In all six samples were analysed, and in each sample the conclusions resulting were of a nature sufficiently serious to support the view that the bacterial flora was not inferior to ordinary sewage. The water in which the ice-cream glasses were washed was also examined, and found to contain large numbers of bacteria.
Since that date many investigations have been made into ice-creams. It appears that they are often made under extremely foul circumstances, and with anything but sterilised appliances. Little wonder, then, that the numbers of bacteria present run into millions. In nearly all recorded cases the quality of the germs as well as the quantity has been of a nature to cause some concern. Bacillus coli communis, which, though not now considered absolutely indicative of alimentary pollution, is looked upon as a highly unsatisfactory inhabitant of water, has been found in considerable abundance. The Proteus family, which also possesses a putrefactive function, is common in ice-creams. The common water bacteria are nearly always present.
Bacillus typhosus itself, it is said, has been isolated from some ice-cream which was held responsible for an outbreak of enteric fever. The material had become infected during process of manufacture in the house of a person suffering from unnotified typhoid fever.
Now, whilst reports of the above nature appear very alarming, the fact is that hundreds of weakly children devour ice-cream with apparent impunity, and when evil follows it is not infrequently due to other than bacterial conditions. The cold mass itself may inhibit the resistance of the gastric tissues. Tyrotoxicon, the alkaloid separated from cheese and cream by Vaughan, may be responsible for some alimentary irritation. On the whole, the practical effect upon the community is not in proportion to the bacterial content of the ice-cream. Yet, nevertheless, we ought to be much more watchful than in the past to preserve ice-cream from pollution with harmful bacteria.
The two chief constituents which contribute their quota of germ life to ice-cream are ice and cream. In addition, the uncleanly methods of manufacture render the material likely to contain the six or seven millions of micro-organisms per cc. which have been on several occasions estimated. To cleanly methods of dairying we have already fully referred; to the bacterial content of milk and cream we have also paid some attention; but we have not had an opportunity of saying anything of germs in ice.
Ice contains bacteria in varying quantities from 20 per cc. to 10,000 or more. Nor is variation in number affected alone by the condition of the water, for samples collected from one and the same place differ widely. The quality follows in large measure the standard of the water.
Water bacteria, Bacillus coli, putrefactive bacteria, and even pathogenic have been found in ice. Many of the latter can live without much difficulty and are most numerous in ice containing air-bubbles.
Dr. Prudden, of New York, performed a series of experiments in 1887 to show the relative behaviour of bacteria in ice. Taking half a dozen species, he inoculated sterilised water and reduced it to a very low temperature for a hundred and three days, with the following results:—Bacillus prodigiosus diminished from 6,300 per cc. to 3,000 within the first four days, to 22 in thirty-seven days, and vanished altogether in fifty-one days; a liquefying water bacillus, numbering 800,000 per cc. at the commencement, had disappeared in four days; Staphylococcus pyogenes aureus and B. fluorescens showed large numbers present at the end of sixty-six and seventy-seven days respectively; B. typhosus, which was present 1,000,000 per cc. after eleven days, fell to 72,000 after 77 days, and 7,000 at the end of 103 days. Anthrax bacilli are susceptible to freezing, but their spores are practically unaffected (Frankland).
From these facts it will be seen that bacteria live, but do not multiply, in ice.
In making a bacterial investigation into the flora of ice-cream, it is necessary to remember that considerable dilution with sterilised water is required. The usual methods of examining water and milk are adopted.
Bread forms an excellent medium for moulds, but unless specially exposed the bacteria in it are few. Waldo and Walsh have, however, demonstrated that baking does not sterilise the interior of bread. These observers cultivated numerous bacteria from the centre of newly baked London loaves.[76] The writer has recently made a series of examinations of the air of several underground bakehouses in Central London; but, though the air was highly impregnated with flour-dust, few bacteria were present.
Other foods and beverages may be, and are, from time to time contaminated in some small degree with bacteria or their spores. Such contaminations are generally due to uncleanly manufacture or unprotected storage. The principles of examination or of the prevention of pollution are similar to those already described.
CHAPTER VII
THE QUESTION OF IMMUNITY AND ANTITOXINS
THE term natural immunity is used to denote natural resistance to some particular specific disease. It may refer to race, or age, or individual idiosyncrasies. We not infrequently meet with examples of this freedom from disease. Certain races of men do not, as a rule, take certain diseases. For example, plague and leprosy, though endemic in some countries, fail to get a footing in England. This, of course, is due in great measure to the sanitary organisation and cleanly customs of the English people. Still, it is also due to the fact that the English appear in some degree to be immune. Some authorities hold that the immunity against leprosy is due to the fact that the disease has exhausted itself in the English race. However that may be, we know that immunity, entire or partial, exists. Children, again, are susceptible to certain diseases and insusceptible to certain others to which older people are susceptible. We know, too, that some individuals have a marked protection against some diseases. Some people coming into the way of infection at once fall victims to the disease, whilst others appear to be proof against it. It is only in recent times that any very intelligent explanations have been offered to account for this phenomenon. The most recent of these, and that which appears to have most to substantiate it, is known as immunity due to antitoxins.
The products of bacteria are chiefly six:
1. Pigment. We have already seen how many organisms exhibit their energy in the formation of many coloured pigments. They are, as a rule, "innocent" microbes. Oxygen is required for some, darkness for others, and they all vary according to the medium upon which they are growing. Red milk, yellow milk, and green pus afford examples of pigment produced by bacteria.
2. Gas. Quite a number of the common bacteria, like Bacillus coli, produce gas in their growth; hydrogen (H), carbonic acid (CO2), methane (CH4), and even nitrogen (N) being formed by different bacteria. Many gases produced during fermentative processes are the result, not directly of the growth of the bacillus causing the fermentation, but indirectly owing to the splitting up of the fermenting fluids.
3. Acids. Lactic, acetic, butyric, etc., are common types of acids resulting from the growth of bacteria.
4. Liquefying Ferment. As we have seen, bacteria may be classified with regard to their behaviour in gelatine medium, whether or not they produce a peptonising ferment which liquefies the gelatine.
5. Phosphorescence. Some species of bacteria in sea-water possess the power of producing light.
6. Organic Chemical Products. When a pathogenic bacillus grows either in the body or in a test-tube, it produces as a result of its metabolism certain poisonous substances called toxins. These may occur in the blood as a direct result of the life of the bacillus, or they may occur as the result of a ferment produced by the bacillus. They are of various kinds according to the various diseases, and by their effect upon the blood and body tissues they cause the symptoms of the disease in question. We know, for instance, that a characteristic symptom common to many diseases is fever. Now, fever is produced by the action of the albumoses (bodies allied to the proteids) upon the heat-regulating centres in the brain. Whenever we get a bacillus growing in the body which has the power of producing a toxin albumose, we get fever as a result of that product acting upon the brain. Albumoses, as a matter of fact, cause a number of symptoms and poisonous effects, but the mention of one as an illustration will suffice. Toxins act, roughly speaking, in two ways:
(1) They have a local action, as, for example, in the formation of an abscess. The presence of the causal bacteria in the tissue brings about very marked changes. There is a multiplication of connective-tissue corpuscles, an emigration of leucocytic cells, a congestion of blood corpuscles. All these elements assist in creating a swelling and redness, and pain by the subsequent pressure upon the delicate nerve endings. These, as we all know, are the symptoms of a "gathering" or abscess. It is a "gathering" in a strict pathological sense—a gathering of cells to oust the intruder or build around it a wall or capsule as a protective measure. Now the toxin will commence its local action. The oldest cells in the mass of congestion will be caused to break down into liquid; what is called a necrosis, or death, will rapidly set in; and we shall have the connective-tissue cells, leucocytes, blood corpuscles, etc., losing their form and function, and "coming to a point" as matter, or pus. The local breaking down of these gatherings of cells into fluid matter is believed to be the work, not of the bacteria themselves, but of their toxins.
(2) Toxins may be absorbed and distributed generally throughout the body. They produce degenerative changes in muscles, in organs, and in the blood itself. Let us take diphtheria as an example. The bacillus occurs in a false membrane in the throat and occasionally other parts. It causes first the inflammatory condition giving rise to the membrane, and then it breaks it down. In the body of the membrane the bacillus appears to secrete a ferment which by its action and interaction with the body cells and proteids, chiefly those of the spleen, produces albumoses and an organic acid. These latter bodies are the toxins. They are absorbed, and pass throughout the body. There are albumoses, therefore we get the frequent pulse and high temperature of fever; the toxins irritate the mucous membrane of the intestine, and cause various fermentative changes in the contents of the intestine, therefore we get the symptoms of diarrhœa; they penetrate the liver, spleen, and kidney, therefore we get fatty degeneration and its results in these organs; they finally affect many of the motor and sensory nerves, breaking up their axis cylinders into globules, and therefore we get the characteristic paralysis. Loss of weight naturally follows many of these degenerative or wasting changes. Here, then, we have some of the chief changes set up by the toxins, and these changes constitute the leading symptoms in the disease as it is known clinically.
In addition to the presence of the specific bacillus in the membrane, we also have a number of other organisms, like the Bacillus coli, Coccus Brissou, Streptococcus pyogenes, and various staphylococci, diplococci, etc. Each of these produces or endeavours in the midst of keen competition and strife to produce, its own specific effect. Thus we obtain the complications of diphtheria, for example various suppurative and septic conditions. The whole of this compound process we may tabulate roughly as follows[77]:
| Bacillus coli. Coccus Brissou. Staphylococci. Diplococci. Streptococci. xxxxxx│ xxxxxx│ Toxins. xxxxxx│ xxxxxx│ Suppurative glands, septic poisoning, etc. | Bacillus of Diphtheria xxxxxxxxx│ | = primary infective agent | |
| Inflammatory changes and fibrinous exudation. xxxxxxxxx│ | |||
| Ferment in Membrane xxxxxxxxx│ | = secondary infective agent | ||
| Passes through body, and by digestion of proteids produces |  | ALBUMOSES; AN ORGANIC ACID | |
| xxxxxx│ xxxxxx│ | |||
| 1. Fever. 2. Diarrhœa. 3. Loss of body weight. 4. Fatty degeneration. 5. Degeneration of peripheral | |||
Such is the general effect of toxins in diphtheria. The same principles apply with equal force in tetanus, typhoid, etc., the only differences being in degree of virulence, mode of onset, and portions of the body chiefly affected.
Sidney Martin has recently[78] elaborated the views announced by him in 1892, and it is right that reference should be made to his new classification of bacterial poisons. This may be represented as follows:—
1. The poisons secreted by the bacterium itself = (ferment? toxin?) |  | = Extracellular bacterial poisons. |
2. Products of digestive action of bacterium = albumoses: | ||
3. Final non-proteid products = animal alkaloid; | ||
4. Poisons present in the bodies of the bacillus | = Intracellular bacterial poisons. | |
The poisons of bacteria are, according to Sidney Martin, of a kind which cannot be fully expressed chemically, but only pathologically. They may be of a ferment nature in diphtheria and tetanus. The arguments in support of that view are—(1) that they act in infinitesimal doses, (2) that they may act slowly and produce death after many days by profoundly affecting the general nutrition, and (3) that they are sensitive to the action of heat in a way that no chemical poisons are known to be. If they are considered as ferments, they must be substances which have a peculiar affinity for certain tissues of the body on which they produce their special toxic effect. As for the products of digestion, they are formed either by the bacillus ingesting the proteid and discharging it as albumose, or the digestion occurs by means of a ferment secreted by the bacillus in the body of an individual or animal suffering from the disease.
Sidney Martin suggests that anthrax produces albumoses and an alkaloidal substance, the former producing fever, the latter stupor. In tetanus the bacillus produces a secretion of the bacillus which causes the convulsions. The albumoses present in this disease are probably due to the secretory toxin. In diphtheria, too, we have a secretory poison in the membrane and in the tissues, and an albumose which is possibly the result of the secretion. It will be seen that these views differ in some particulars from those to which we have already referred.
However the details of the modus operandi of the formation of toxins are finally settled, we know that there comes a time when the disease symptoms vanish, the disease declines, and the patient recovers. Many of the older schools of medicine explained this satisfactory phenomenon by saying that this disease exhausted itself after having "gone through" the body. In a sense that idea is probably true; but recently a large number of investigators have applied themselves to this problem, and with some promising results.
Various protective inoculations against anthrax were practised as early as 1881, and the protected animals remained healthy. In 1887 Wooldridge succeeded in protecting rabbits from anthrax by a new method, by which he showed that the growth of the anthrax bacillus in special culture fluids gave rise to a substance which, when inoculated, conferred immunity. In 1889 and 1890 Hankin and Ogata worked at the subject, and announced the discovery in the blood of animals which had died of anthrax of some substances which appeared to have an antagonistic and neutralising effect upon the toxins of anthrax and upon the anthrax bacilli themselves. These substances, they afterwards found, were products of the anthrax bacillus. Behring and Kitasato arrived at much the same results for tetanus and diphtheria. The next step was to isolate these substances, and, separating them from the blood, investigate still further their constitution. A number of workers were soon occupied at this task, and since 1891 Buchner, Hankin, the Klemperers, Roux, Sidney Martin, and others have added to our knowledge respecting these toxin-opposing bodies known as antitoxins. In diphtheria, as we have seen, the toxins turned out to be soluble bodies allied to the proteids, albumoses, and an organic acid. Then arose the question of the source of antitoxins. Some believed they were a kind of ultratoxin—bodies of which an early form was a toxin; others held that, as the toxins were products of the bacteria invading the tissues, the antitoxins were of the nature of ferments produced by the resisting tissues. Finally, they came to be looked upon as protective substances produced in the body cells as a result of toxin action, and held in solution in the blood, and there and elsewhere exerting their influence in opposition to the toxins.[79] The progress of disease is therefore a struggle between the toxins and the antitoxins: when the toxins are in the ascendency we get an increase of the disease; when the antitoxins are in the ascendency we get a diminution of disease. If the toxins triumph, the result is death; if the antitoxins and resistance of the tissues triumph, the result is recovery.
We may now consider shortly how these new facts were received and what theories of explanation were put forward to explain continued insusceptibility to disease. It had of course been known for a long time past that one attack of small-pox, for example, in some degree protected the individual from a subsequent attack of the same disease. To that experience it was now necessary to add a large mass of experimental evidence with regard to toxins and antitoxins. The theories of immunity were as follows:
1. The Exhaustion Theory. The supporters of this idea argued that bacteria of disease circulating in the body exhausted the body of the supply of some substance or condition necessary for the growth and development of their own species.
2. The Retention Theory. It was surmised that there were certain products of micro-organisms of disease retained in the body after an attack which acted antagonistically to the further growth in the body of that same species.
3. The Acquired Tolerance Theory. Some have advanced the theory that, after a certain time, the human tissues acquired such a degree of tolerance to the specific bacteria or their specific products that no result followed their action in the body. The tissues become acclimatised to the disease.
4. The Phagocyte Theory. This theory, which gained so many adherents when first promulgated by Metschnikoff, attributes to certain cells in the tissues the powers of "scavenging," overtaking germs of disease, and absorbing them into their own protoplasm. This, indeed, may be actually witnessed, and had been observed before the time of Metschnikoff. But it was he who applied it to disease. He came to the conclusion that the successful resistance which an animal offered to bacteria depended upon the activity of these scavenging cells, or phagocytes. These cells are derived from various cellular elements normally present in the body: leucocytes, endothelial cells, connective-tissue corpuscles, and any and all cells in the body which possess the power of ingesting bacteria. If they are present in large numbers and active, the animal is insusceptible to certain diseases; if they are few and inactive, the animal is susceptible.
It appears that the bacteria or other foreign bodies in the blood which are attacked by the phagocyte become assimilated until they are a part of the phagocyte itself. Metschnikoff explained also how it comes to pass that the phagocyte is able to encounter bacteria when both are circulating through the blood. It is guided in this attack upon the organisms by a power termed chemiotaxis. The bacteria elaborate a chemical substance which attracts the phagocyte, and this is termed "positive chemiotaxis."[80] But it may occur that the chemical substance produced by the bacteria may have an opposite, or repellent, effect upon the leucocytes, in which case we have "negative chemiotaxis."[81] It is not to be wondered at that such a theory of immunity based upon microscopical observations, should at first have been widely accepted, and there can be no doubt that Metschnikoff has collected a considerable mass of evidence in support of a theory of phagocytosis. But when it came to be known that blood serum, from which all leucocytes (phagocytes) had been removed, possessed the same immunising effect as before, it was clear that such effect was a property of the serum per se, and not only or wholly due to the scavenging power of certain cells in it. Even the phagocyte theory depends largely for its validity upon chemiotaxis, which latter was a property of the products of the bacteria contained in the blood serum.
5. The Antitoxin Theory. We have gathered, then, that whenever bacteria, introduced into the blood and tissues, fail to multiply or produce infection (as in saprophytic bacteria, or in immunity of a particular animal from a specific microbe), this inability to perform their rôle is brought about by some property in the living and normal blood serum which opposes their life and action; and further we have learned that this protective property is exhaustible according to the number of bacteria, and differs with various species of bacteria, and in different animals. Buchner designates these protective bodies, held in solution in the blood, alexines, and regards them as belonging to the albuminous bodies of the lymph and plasma. Where the blood and tissues do not possess this power, the animal is susceptible. Now, as we have already seen from the experiments of Ogata, Kitasato, and others, the blood of an animal dead of anthrax is protective against anthrax, from which and the foregoing it appears that microbes produce by their growth in the tissues poisonous substances we term toxins, which have the power of producing in the blood and body cells substances inimical to themselves, named antitoxins, and so long as these latter substances remain in the tissues the body remains insusceptible to further attacks of the same disease. Alexines are naturally produced antitoxins; antitoxins are acquired alexines. Hence we have the well-known terms "natural" and "acquired immunity." Of the former we have already spoken. Acquired immunity is a protection not belonging to the tissues of individuals naturally and as part of their constitution, but it is acquired during their lives as a further accomplishment, so to speak, of their tissues. This may happen in one or both of two ways. Either it may be an involuntary acquired immunity, or a voluntary acquired immunity. For example, the former is at once illustrated by an attack of the disease.
Small-pox, typhoid fever, even scarlet fever, are diseases which very rarely attack the same individual twice. That is because each of these diseases leaves behind it, on its first appearance, its antitoxic influence. Hence the individual has involuntarily acquired immunity against these diseases. An example of voluntary acquired immunity is also at hand in the old method of preventive inoculation for small-pox, or variolation. This was clearly an inoculation setting up an artificial and mild attack of small-pox, by which the antitoxins of that disease were produced, and protected the individual against further infection of small-pox; that is to say, it was a voluntary acquired immunity. This form of artificial production of protection is generally called artificial immunity. Let us now marshal together these various terms in a table as follows:
| Immunity in man = a condition of protection of insusceptibility to certaindiseases. | ||
| 1. Natural immunity = constitutional protection produced by alexines. | ||
| 2. Acquired immunity | ||
| = |  | Acquired naturally (involuntarily) produced by antitoxins formed byan attack of the disease. |
| Acquired artificially (voluntary)= | ||
(a) Active immunity, produced by direct inoculation of the weakenedbacteria or weakened toxins of the disease, e. g., vaccination,or Pasteur's treatment of rabies, or Haffkine'sinoculation for cholera. | ||
(b) Passive immunity, produced by inoculation, not of the diseaseof an animal suffering from the specific disease. | ||
It is hoped that previous remarks will have explained the meaning of the terms used in the above table, with the exception of the last two phrases of active and passive immunity. We propose now to consider in some detail the four illustrations quoted under these two headings, viz., vaccination, Pasteur's treatment of rabies, anti-cholera inoculation, and antitoxin inoculation. From all accounts, it is to be feared that these four phases of artificial immunity are hopelessly confused in the educated public mind. Nor is this to be wondered at when we reflect upon the rapid growth of the whole science of immunity, and upon the ever-varying forms of nomenclature through which it has passed.
Vaccination for Small-pox. In 1717 Lady Mary Wortley Montagu[82] described the inoculation of small-pox as she had seen it practised in Constantinople. So greatly was she impressed with the efficacy of this process that she had her own son inoculated there, and in 1721 Mr. Maitland, a surgeon, inoculated her daughter in London. This was the first time inoculation was openly practised in England.[83] For one hundred and twenty years small-pox inoculation (or variolation, as it is more correctly termed) was practised in England, until by Act of Parliament in 1840 it was prohibited.
There were different ways of performing variolation, but the most approved method was similar to the modern system of arm-to-arm vaccination, the arm being inoculated with a lancet in one or more places with small-pox lymph instead of, as now, with vaccine lymph. As a rule, only local results or a mild attack of small-pox followed, which prevented an attack of natural small-pox. Its disadvantage is apparent on the surface. It was a means of breeding small-pox, for the inoculated cases were liable to create fresh centres of infection. In 1796 Edward Jenner, who was a country practitioner in Gloucestershire, observed that those persons affected with cow-pox, contracted in the discharge of their duty as milkers, did not contract small-pox, even when placed in risk of infection. Hence he inferred that inoculation of this mild and non-infectious disease would be preferable to the process of variolation then so widely adopted in England. Jenner therefore suggested the substitution of cow-pox lymph (vaccine) in place of small-pox lymph, as in ordinary variolation.
It should not be forgotten that variolation was thus the first work done in this country in producing artificial immunity, and was followed by vaccination, which was only partly understood. Even to-day there is probably much to learn respecting it. Both variolation and vaccination may be described as active immunisation by means of an attenuated form of the specific virus causing the disease. The nature of the specific virus of both small-pox and cow-pox awaits discovery. Burdon Sanderson, Crookshank, Klein, and Copeman have all demonstrated bacteria in cow-pox or vaccine lymph, and in 1898 Copeman announced that he had isolated a specific bacillus and grown it upon artificial media.[84] Numerous statements have been made to the effect that a specific bacillus has been found in small-pox also. But neither in small-pox nor cow-pox is the nature of the contagion really known.[85]
These facts, however, do not remove the suspicion which has hitherto rested upon vaccine lymph as a vehicle for bacteria of other diseases which by its inoculation may thus be contracted. A few remarks are therefore called for at this juncture upon the recent work of Dr. Monckton Copeman and Dr. Frank Blaxall in respect to what is known as glycerinated calf lymph. Evidence has been forthcoming to substantiate in some measure the distrust which many of the public have from time to time felt in the vaccine commonly used in vaccination, hence the new form as above designated. This retains the toxic qualities required for immunity, but is so produced that it possesses in addition three very important advantages; namely, it is entirely free from extraneous organisms, it is available for a large number of vaccinations, and it retains full activity for eight months. It is prepared as follows:
A calf, aged three to six months, is kept in quarantine for a week. If then found upon examination to be quite healthy, it is removed to the vaccination station, and the lower part of its abdomen antiseptically cleaned. The animal is now vaccinated upon this sterilised area with glycerinated calf lymph. After five days the part is again thoroughly washed, and the contents of the vesicle, which have of course appeared in the interval, are removed with a sterilised sharp spoon, and transferred to a sterilised bottle. This is now removed to the laboratory, and the exact weight of the material ascertained. A calf thus vaccinated will yield from 18 to 24 grams of vaccine material. This is now thoroughly triturated and mixed with six times its weight of a sterilised solution of 50 per cent. chemically pure glycerine in distilled water. The resulting emulsion is aseptically stored in sealed tubes in a cool place. For four weeks it is carefully examined bacteriologically until the glycerine has absolutely killed any possible germ that may have obtained entrance. When by agar plates it is demonstrably sterile it is ready for distribution.
Pasteur's Treatment of Rabies. Rabies is a disease affecting dogs (in Western Europe) and wolves (in Russia), and can be transmitted to other animals and man, infection being carried by the bite of a rabid animal. It takes two chief forms: (1) furious rabies and (2) paralytic rabies. The former is more common in dogs. The animal becomes restless, has a high-toned bark, and snaps at various objects. Sometimes it exhibits depraved appetite; spasms of the throat follow, and these soon develop into convulsions, which are followed by coma and death. In man the incubation period is fortunately a very long one, averaging about forty days. Nervous irritability is the first sign; spasms occur in the respiratory and masticatory muscles, and the termination is similar to rabies in the dog. The symptom of fear of water is a herald of coming fatality.
Although a number of the workers at the Pasteur Institute and elsewhere have addressed themselves to the detection of a specific microbe, none has as yet been found, although, in the opinion of Pasteur, such an agent may be suspected as the cause.
Pathologically rabies and tetanus (see page 168) are closely allied diseases, and the recent remarkable additions to our knowledge of the latter disease only make the similarity more evident. There are in rabies three chief sets of post-mortem signs. First, and by far the most important, are the changes in the nervous system. Here we find patches of congestion in the brain, and breaking down of the axis cylinders of the nerves. The stomach, in the second place, exhibits hæmorrhagic changes, not unlike acute arsenical poisoning. Thirdly, the salivary glands show a degenerative change in a breaking down of their secreting cells. Roux has pointed out that in life the saliva of a mad dog becomes virulent three days before the appearance of the symptoms of disease.
We may now turn to the method of treatment which was introduced by Pasteur. Before his time cauterisation of the wound was the only means adopted. If more than half an hour has elapsed since the bite, cauterisation is of little or no avail. The basis for Pasteur's treatment was the difference in virulence obtainable in spinal cords infected with rabies. Pasteur found that drying the cord led to a lessening of its virulence, just as certain other conditions increased its virulence. Next he established the fact that subcutaneous injection of a weak virus, followed up with doses of ever-increasingly virulent cords, immunised dogs against infection or inoculation of fully virulent material. From this he reasoned that if he could establish a standard of weakened virulence he would have at hand the necessary "vaccine" for the treatment of the disease.
Subsequent research and skilled technique resulted in a method of securing this standard, which he found to be a
Suspended Spinal Cord
In drying jar containing Calcium Chloride spinal cord dried for fourteen days. The exact details are as follows: The spinal cords of two rabbits dead of rabies are removed from the spinal canal in their entirety by means of snipping the transverse processes of the vertebrae. Each cord is divided into three more or less equal pieces, and each piece, being snared by a thread of sterilised silk, is carefully suspended in a sterilised glass jar. At the bottom of the jar is a layer, about half an inch deep, of sterilised calcium chloride. The jars are then removed to a dark chamber, where they are placed at a temperature of 20–22° C. in wooden cases. Here they are left to dry. Above each case is a tube of broth, to which has been added a small piece of the corresponding cord, in order to test for any organismal element that may by chance be included. In case of the slightest turbidity in the broth, the cord is rejected. Fourteen series of cords are thus suspended on fourteen consecutive days. The first, second, and third are found to be of practically equal virulence, but from the third to the fourteenth the virulence proportionately decreases, and on the fifteenth day the cord would be practically innocuous and non-virulent. When treatment is to be commenced, obviously the weakest—that is, the fourteenth day—cord is used to make the "vaccine," and so on in steadily increasing doses (as regards virulence) up to and including a third-day cord. The fourteenth-day cord is therefore taken, and a small piece cut off and macerated in 10 cc. of sterile broth, which are placed in a conical glass and covered with two layers of thick filter-paper, the glass with its covering having been previously sterilised by dry heat. When the patient bitten by the rabid animal is prepared, 3 cc. of this broth emulsion of spinal cord are inoculated by means of a hypodermic needle into the flanks or abdominal wall. On the following day the patient returns for an inoculation of a cord of the thirteenth day, and so on until a rabid cord emulsion of the first three days has been inoculated. As a matter of practice, the dosage depends upon the three recognised classes of bites, viz. (1) bites through clothing (least severe); (2) bites on the bare skin of the hand; (3) bites upon the face or head, most severe owing to the vascularity of these parts. An example of each, which the writer was permitted to take in the Pasteur Institute, may be here added to make quite clear the entire practice. (See page [258.])
It may be well to add the returns of inoculation made at the Pasteur Institute, Rue Dutot, Paris, as above described. They are as follows:
Pasteur's treatment of rabies by inoculation of emulsions of dried spinal cord is, therefore, a "vaccination" of attenuated virus, resulting in antitoxin formation, to the further protection of the individual against rabies.
One further example of the modern application of the principles of active acquired immunity may be shortly mentioned. We refer to the cholera and plague vaccinations. The vaccination in small-pox is an inoculation of the virus of the disease; the rabies inoculation is a transmission of the vital products of the disease attenuated; the plague and cholera vaccinations are inoculations of pure cultures of living virus from outside the body. Inoculating cholera virus against cholera has been made illegal, as variolation was in 1840. But Haffkine has prepared two vaccines. The weak one is made from pure cultures of Koch's spirillum of Asiatic cholera, attenuated by growth to several generations on agar or broth at 39°C. The strong one is from similar culture the virulence of which has been increased. One cubic centimetre of the first vaccine is injected hypodermically into the flank, and the second vaccine three or four days afterwards. The immunisation is prophylactic, not remedial, and its action takes effect five or six days after the second vaccine has been injected.
INOCULATION TREATMENT FOR PERSONS AFFECTED WITH RABIES
| 1. For those Bitten through Clothes | 2. For those Bitten on Uncovered Skin of Hands, Etc. | 3. For those Bitten on Face or Head. | ||||
| Days of Treatment. | Doses of Emulsion per cc. | Dates of Cord Drying. | Doses of Emulsion per cc. | Dates of Cord Drying. | Doses of Emulsion per cc. | Dates of Cord Drying. |
| 1 at 11 A.M. | 3 | 14 | 3 | 14 | 3 | 14 |
| 1 at"11ii"A | 3 | 13 | 3 | 13 | 3 | 13 |
| 1 at 3 P.M. | .. | .. | .. | .. | 3 | 12 |
| 1 at"11ii"A | .. | .. | .. | .. | 3 | 11 |
| 2 at 11 A.M. | 3 | 12 | 3 | 12 | 3 | 10 |
| 2 at"11ii"A | 3 | 11 | 3 | 11 | 3 | 9 |
| 2 " 3 P.M. | .. | .. | .. | .. | 3 | 8 |
| 2 at"11ii"A | .. | .. | .. | .. | 3 | 7 |
| 3 at 11 A.M. | 3 | 10 | 3 | 10 | 3 | 6 |
| 3 at"11ii"A | 3 | 9 | 3 | 9 | 3 | 6 |
| 4 at 11 A.M. | 3 | 8 | 3 | 8 | 3 | 5 |
| 4 at"11ii"A | 3 | 7 | 3 | 7 | .. | .. |
| 5 at"11ii"A | 3 | 6 | 3 | 6 | 3 | 5 |
| 5 at"11ii"A | 3 | 6 | 3 | 6 | .. | .. |
| 6 at"11ii"A | 3 | 5 | 3 | 5 | 3 | 4 |
| 7 at"11ii"A | 3 | 5 | 3 | 5 | 2 | 3 |
| 8 at"11ii"A | 3 | 4 | 3 | 4 | 3 | 4 |
| 9 at"11ii"A | 2 | 3 | 2 | 3 | 3 | 3 |
| 10 at"11ii"A | 3 | 5 | 3 | 5 | 3 | 5 |
| 11 at"11ii"A | 3 | 5 | 3 | 5 | 3 | 5 |
| 12 at"11ii"A | 3 | 4 | 3 | 4 | 3 | 4 |
| 13 at"11ii"A | 3 | 4 | 3 | 4 | 3 | 4 |
| 14 at"11ii"A | 3 | 3 | 3 | 3 | 3 | 3 |
| 15 at"11ii"A | 3 | 3 | 3 | 3 | 3 | 3 |
| 16 at"11ii"A | ... | .. | 3 | 5 | 3 | 5 |
| 17 at"11ii"A | ... | .. | 3 | 4 | 3 | 4 |
| 18 at"11ii"A | ... | .. | 3 | 3 | 3 | 3 |
| 19 at"11ii"A | .. | .. | .. | .. | 3 | 5 |
| 20 at"11ii"A | .. | .. | .. | .. | 3 | 4 |
| 21 at"11ii"A | .. | .. | .. | .. | 3 | 3 |
In plague the same plan has been followed. Luxurious crops of Kitasato's plague bacillus are grown on ordinary nutritive media plus large quantities of fat. The fat of milk, as clarified butter, is that generally used. Under the globules of fat flakes of culture grow like stalactites, hanging down into the clear broth. These are in time shaken to the bottom, and a second crop grows on the under-surface of the fat. In the course of a month perhaps half a dozen such crops are obtained and shaken down into the fluid, until the latter assumes an opaque milky appearance. This is now, unlike the cholera vaccine, exposed to a temperature of 70° C., by which the microbes are killed. The culture contains all the toxins, and the dose is 3 cc. This preparation has the advantage of being easily prepared, obtainable in large quantities, and requires no animals in its preparation. When inoculated it produces local pain and swelling at the site of inoculation, and general reactive symptoms such as fever. From a careful analysis of the results of this inoculation, it is shown that the efficacy of the prophylactic depends upon the virulence of the bacillus culture from which the vaccine is prepared, and upon its dose and ability to produce a well-marked febrile reaction. It appears to be more effective in the prevention of deaths than of attacks.
The anti-typhoid vaccination is another example of inoculation to secure active immunity. It is needless, perhaps, to point out that all these vaccinations, except rabies, are prophylactic, and not curative.
Passive Immunity; Preparation of Antitoxins. We must now consider the question of passive immunity. This, it will be remembered, may be defined as a protection (against a bacterial disease) produced by inoculation, not of the disease itself, as in small-pox inoculation, nor yet of its weakened toxins, as in rabies, but of the antitoxins produced in the body of an animal suffering from that particular disease. Examples of this treatment are increasing every year, and the term "antitoxin" has now become almost a household word. The chief examples are to be found in diphtheria, tetanus, streptococcus, and pneumococcus.
To be of value, antitoxins must be used as early as possible, before tissue change has occurred and before the toxins have, so to speak, got the upper hand. When the toxins are in the ascendency the patient suffers more and more acutely, and may succumb before there has been time for the formation in his own body of the antitoxins. If he can be tided over the "crisis," theoretically all will be well, because then his own antitoxin will eventually gain the upper hand. But in the meantime, before that condition of affairs, the only way is to inject antitoxins prepared in some animal's tissues whose disease began at an earlier date, and thus add antitoxins to the blood of our patient, early in the disease, and the earlier the better, for, however soon this is done, it is obvious that the toxins begin their work earlier still. It should not be necessary to add that general treatment must also be continued, and indeed local germicidal treatment, e. g., of the throat in diphtheria and the poisoned wound in tetanus. Further, in a mixed infection, as in glandular abscesses with diphtheria, it must be borne in mind that the antitoxin is specific and may therefore probably fail in such mixed cases.
After these preliminary remarks we will now consider shortly some of the methods employed for the production of antitoxins. An animal is required from whose body a considerable quantity of blood can be drawn without injurious effect. Moreover, it must be an animal that can stand an attack of such diseases as diphtheria and tetanus. Such an animal is the horse. Now, by injecting into the horse (a) living organisms of the specific disease, but in non-fatal doses, or (b) dead cultures, or (c) filtered cultures containing no bacteria and only the toxins, we are able to produce in the blood of the horse first the toxins and then the antitoxins of the disease in question. The non-poisonous doses of living organisms can be weakened, or, as we say, attenuated, by various means. Dead cultures have not been much used to produce immunity except by Pfeiffer. In actual practice the third method is much the most general, viz., filtering a fluid culture free from the bacteria, and then inoculating this in ever-increasing doses. The preparation of diphtheria antitoxin may be taken as an example, but what follows would be equally applicable to other diseases, such as tetanus.
1. To Obtain the Toxin. First grow a pure culture of the Klebs-Löffler bacillus of diphtheria in large flasks containing "Löffler's medium," or a solution made by mixing three parts of blood serum with one of beef broth and adding one per cent. of common salt (Na Cl) and one per cent. of peptone. An alkaline medium is preferable. The flask
Flask used for the Preparation of the Toxin of Diphtheria was thoroughly sterilised before use, and is now plugged with sterile cotton-wool and incubated at 77° C. for three or four weeks. Pure air may be passed over the culture periodically, thereby aiding the growth. After the lapse of about a month a scum of diphtheria growth will have appeared over the surface of the fluid. This is now filtered into sterilised flasks, and some favourable antiseptic added to ensure that nothing foreign to the toxin shall flourish, and the flasks are kept in the dark. Here, then, we have the product, the toxin, ready for injection into the horse.
2. Immunisation of the Horse. It is evident that only healthy horses are of service in providing healthy antitoxin, even as healthy children are necessary in arm-to-arm vaccination. To provide against any serious taint the horse is tested for glanders (with mallein) and for tuberculosis (with tuberculin). The dose of the injection of toxin is at the commencement about 1/10 cc., or a little more. The site of the inoculation is the apex of the shoulder, which has been antiseptically cleaned. A mere prick is the whole operation. After the first injection there is generally a definite febrile reaction and a slight local swelling. From 1/10 or 1/2 cc. the dose is steadily increased, until at the end of two or three months[86] perhaps as much as 300 cc. (or even half a litre) may be injected without causing the reaction which the initial injection of 1/10 cc. caused at the outset. This shows an acquired tolerance of the tissues of the horse to the toxic material. After injecting 500 cc. into the horse without bad effect, the animal has a rest of four or five days.
3. To Obtain the Antitoxin. During this period of rest the interaction between the living body cells of the animal and the toxins results in the production in the blood of an antitoxin. By means of a small sterilised cannula, five, or eight, or even ten litres of blood are drawn from the jugular vein of the horse into sterilised flasks or jars. The top of the jar is closed by two paper coverings before it is sterilised. Then it is again covered with a further loose one. Before use the loose one is removed and replaced by a metal (zinc) lid, which has been separately sterilised. This metal lid contains an aperture large enough for the tube which conveys the blood from the cannula to pass through. The tube, therefore, passes through the metal lid and two paper covers, which it was made to pierce. When enough blood has passed into the vessel the tube is withdrawn, and the metal lid slightly turned. Thus the contained blood is protected from the air.[87]
The jar containing the blood (which contains the antitoxin) is next placed in a dark, cool cellar, where it stands for two or three days. During this time the blood naturally coagulates, the corpuscles falling as a dense clot to the bottom, and the faintly yellow serum rising to the top. The serum, or liquor sanguinis, averages about 50 per cent. of the total blood taken. Sometimes antiseptics are added with a view to preservation. It is generally filtered before bottling for therapeutic use, and sometimes examined bacteriologically as a test of purity.
4. The Use of Antitoxins. The antitoxins are now ready for injection into the patient who has contracted diphtheria, and in whose blood toxins are in the ascendency and under which the individual may succumb. They are injected in varying doses, as we have already pointed out.[88] The general result is that mortality has been greatly lessened, and that in fatal cases there has been a considerable lengthening of the period of life. Moreover, the whole clinical course of the disease has been greatly modified, and suffering lessened.[89]
CHAPTER VIII
BACTERIA AND DISEASE
Probably the most universally known fact respecting bacteria is that they are related in some way to the production of disease. Yet we have seen that it was not as disease-producing agents that they were first studied. Indeed, it is only within comparatively the latest period of the two centuries during which they have been more or less under observation that our knowledge of them as causes of disease has assumed any exactitude or general recognition. Nor is this surprising, for although an intimate relationship between fermentation and disease had been hinted at in the middle of the seventeenth century, it was not till the time of Pasteur that the bacterial cause of fermentation was experimentally and finally established.
In the middle of the seventeenth century men learned, through the eyes of Leeuwenhoek, that drops of water contained "moving animalcules." A hundred years later Spallanzani demonstrated the fact that putrefaction and fermentation were set up in boiled vegetable infusions when outside air was admitted, but when it was withheld from these boiled infusions no such change occurred. Almost a hundred years more passed before the epoch-making work of Tyndall and Pasteur, who separated these putrefactive germs from the air. Quickly following in their footsteps came Davaine and Pollender, who found in the blood of animals suffering from anthrax the now well-known specific and causal bacillus of that disease. Improvements in the microscope and in methods of cultivation (Koch's plate method in particular) soon brought an army of zealous investigators into the field, and during the last twenty years first this disease and then that have been traced to a bacterial origin. We may summarise the vast mass of historical, physiological, and pathological research extending from 1650 to 1898 in three great periods: the period of detection of living, moving cells (Leeuwenhoek and others in the seventeenth century); the period of the discovery of their close relationship to fermentation and putrefaction (Spallanzani, Schulze, Schwann, in the eighteenth century); and, thirdly, the period of appreciation of the rôle of bacteria in the economy of nature and in the production of disease (Tyndall, Pasteur, Lister, Koch, in the nineteenth).
But we must look less cursorily at the growth of the idea of bacteria causing disease. More than two hundred years ago Robert Boyle (1627–91), the philosopher, who did so much towards the foundation of the present Royal Society, wrote a learned treatise on The Pathological Part of Physic. He was one of the earliest scientists to declare that a relationship existed between fermentation and disease. When more accurate knowledge was attained respecting fermentation, great advance was consequently made in the etiology of disease. The preliminary discoveries of Fuchs and others between 1840 and 1850 had relation to the existence in diseased tissues of a large number of bacteria. But this was no proof that such germs caused such diseases. It was not till Davaine had inoculated healthy animals with bacilli from the blood of an anthrax carcass, and had thus produced the disease, that reliance could be placed upon that bacillus as the vera causa of anthrax. Too much emphasis cannot be laid upon this idea, that unless a certain organism produces in healthy tissues the disease in question, it cannot be considered as proven that the particular organism is related to the disease as cause to effect. In order to secure a standard by which all investigators should test their results, Koch introduced four postulates. Until each of the four has been fulfilled, the final conclusion respecting the causal agent must be considered sub judice. The postulates are as follows:
(a) The organism must be demonstrated in the circulation or tissues of the diseased animal.
(b) The organism thus demonstrated must be cultivated in artificial media outside the body, and successive generations of a pure culture of that organism must be obtained.
(c) Such pure cultures must, when introduced into a healthy and susceptible animal, produce the specific disease.
(d) The organism must be found and isolated from the circulation or tissues of the inoculated animal.
It is evident that there are some diseases—for example, cholera, leprosy, and typhoid—which are not communicable to lower animals, and therefore their virus cannot be made to fulfil postulate (c). In such cases there is no choice. They cannot be classified along with tubercle and anthrax. Bacteriologists have little doubt that Hansen's bacillus of leprosy is the cause of that disease, yet it has not fulfilled postulates (b) and (c). Nor has the generally accepted bacillus of typhoid fulfilled postulate (c), yet by the majority it is provisionally accepted as the agent in producing typhoid. Hence it will be seen that, though there is an academical classification of causal pathogenic bacteria according as they respond to Koch's postulates, yet nevertheless, there are a number of pathogenic bacteria which are looked upon as causes of disease provisionally. Anthrax and tubercle, with perhaps the organisms of suppuration, tetanus, plague, and actinomycosis, stand in the first order of pathogenic germs. Then comes a group awaiting further confirmation. It includes the organisms related to typhoid, cholera, malaria, leprosy, diarrhœa,and pneumonia. Then comes in a third category, a long list of diseases, such as scarlet fever, small-pox, rabies, and others too numerous to mention, in which the nature of the causal agent is still unknown. Hence it must not be supposed that every disease has its germ, and without a germ there is no disease. Such universal assertions, though not uncommonly heard, are devoid of accuracy.
In the production of bacterial disease there are two factors. First, there is the body tissue of the individual; secondly, there is the specific organism.
Whatever may be said hereinafter with regard to the power of micro-organisms to cause disease, we must understand one cardinal point, namely, that bacteria are never more than causes, for the nature of disease depends upon the behaviour of the organs or tissues with which the bacteria or their products meet (Virchow). Fortunately for a clear conception of what "organs and tissues" mean, these have been reduced to a common denominator, the cell. Every living organism, of whatever size or kind, and every organ and tissue in that living organism, contains and consists of cells. Further, these cells are composed of organic chemical substances which are not themselves alive, but the mechanical arrangement of which determines the direction and power of their organic activity and of their resistance to the specific agents of disease. With these facts clearly before us, we may hope to gain some insight into the reasons for departure from health.
The normal living tissues have an inimical effect upon bacteria. Saprophytic bacteria of various kinds are normally present on exposed surfaces of skin or mucous membrane. Tissues also which are dead or depressed in vitality from injury or previous disease, but which are still in contact with the tissues, afford an excellent nidus for the growth of bacteria. Still these have not the power, unless specific, to thrive in the normal living tissue. It has been definitely shown that the blood fluids of the body have in their fresh state the germicidal power (alexines) which prevents bacteria from flourishing in them. Such action does undoubtedly depend in measure upon the number of germs as well as their quality, for the killing power of blood and lymph must be limited. Buchner has pointed out that the antagonistic action of these fluids depends in part possibly upon phagocytosis, but largely upon a chemical condition of the serum. The blood, then, is no friend to intruding bacteria. Its efforts are to a certain extent seconded by the lymphoid tissue throughout the body. Rings of lymphoid tissue surround the oral openings of the trachea (windpipe) and œsophagus (gullet); the tonsils are masses of lymphoid tissue. Composed as it is of cells having a germicidal influence when in health, the lymphoid tissue may afford formidable obstruction to intruding germs.
All the foregoing points in one direction, namely, that if the tissues are maintained in sound health, they form a very resistant barrier against bacteria. But we know from experience that a full measure of health is not often the happy condition of human tissues; we have, in short, a variety of circumstances which, as we say, predispose the individual to disease. One of the commonest forms of predisposition is that due to heredity. Probably it is true that what are known as hereditary diseases are due far more to a hereditary predisposition than to any transmission of the virus itself in any form. Antecedent disease predisposes the tissues to form a nidus for bacteria; conditions of environment or personal habits frequently act in the same way. Damp soils must be held responsible for many disasters to health, not directly, but indirectly, by predisposition; dusty trades and injurious occupations have a similar effect. Any one of these three different influences may in a variety of ways affect the tissues and increase their susceptibility to disease. Not infrequently we may get them combined. For example, the following is not an unlikely series of events terminating in consumption (tuberculosis of the lungs):—(a) The individual is predisposed by inheritance to tuberculosis; (b) an ordinary chronic catarrh, which lowers the resisting power of the lungs, may be contracted; (c) the epithelial collections in the air vesicles of the lung—i. e., dead matter attached to the body—afford an excellent nidus for bacteria; (d) owing to occupation, or personal habits, or surroundings, the patient comes within a range of tubercular infection, and the specific bacilli of tubercle gain access to the lungs. The result, it is needless to state, will be a case of consumption more or less acute according to environment and treatment.
The channels of infection by which organisms gain the vantage-ground afforded by the depressed tissues are various, and next to the maintenance of resistant tissues they call for most attention from the physician and surgeon. It is in this field of preventive medicine—that is to say, preventing infective matter from ever entering the tissues at all—that science has triumphed in recent years. It is, in short, applied bacteriology, and therefore claims consideration in this place.
1. Pure Heredity. By this term may be understood the actual transmission from the mother to the unborn child of the specific virus of the disease. That such a conveyance may occur is generally admitted by pathologists, but it is impossible to enter fully into the matter in such a book as the present. Summarily we may say that, though this sort of transmission is possible, it is not frequent, nor is disease appreciably spread through such a channel. Sixty per cent. of consumptives, it has been estimated, have tuberculous progenitors, and this is the highest figure. Many would be justified from experience in placing it at half that number.
2. Inoculation, or inserting virus through a broken surface of skin, is itself a sufficiently obvious mode of infection to call for little comment. Yet it is under this heading that a word must be said of that remarkable application of preventive medicine known as the antiseptic treatment of wounds. When Lord Lister was Professor of Surgery in Glasgow, he was impressed with the greatness of the evil of putrefaction in wounds, which was caused, not by the oxygen of the air, as Liebig had declared, but by the entrance into the wound of fermentative organisms from the air. This was demonstrated by Pasteur, who pointed out that they could not arise de novo in the wound. Hence it appeared to Lister that these fermentative bacteria which produce putrefaction in wounds must either be kept out of the wound altogether, or killed, or their action prevented, in the wound. To keep air away from wounds is an almost impossible task, and thus it came about that wounds were dressed with a solution of carbolic acid.
From time to time examples occur of bacterial disease being directly inoculated in wounds made with polluted instruments, or in cuts made by contaminated broken glass, or in gunshot wounds. Tetanus is, of course, one of the most marked examples.
3. Contagion is a term which has suffered from the many ways in which it has been used. Defined shortly and most simply, we should say a disease is contagious when it can be "caught" by contact, through the unbroken surfaces, between diseased and healthy persons. Ringworm is an example, and there are many others.
4. The Alimentary Canal: Food. The recent Royal Commission on Tuberculosis has collected a large mass of evidence in support of the view that tubercle may be spread by articles of food. Milk and meat from tuberculous animals naturally come in for the largest amount of condemnation. To these matters we refer elsewhere.
5. The Respiratory Tract: Air. The air may become infected with germs of disease from dusty trades, dried sputum, etc. If such infected air be inhaled, pathogenic results will follow, especially if the bacteria are present in sufficient numbers, or meet with devitalised, and therefore non-resisting, tissues.
These, then, are the five possible ways in which germs gain access to the body tissues. The question now arises, How do bacteria, having obtained entrance, set up the process of disease? For a long time pathologists looked upon the action of these microscopic parasites in the body as similar to, if not identical with, the larger parasites sometimes infesting the human body. Their work was viewed as a devouring of the tissues of the body. Now, it is well known that, however much or little of this may be done, the specific action of pathogenic bacteria is of a different nature. It is twofold. We have the action of the bacteria themselves, and also of their products or toxins. In particular diseases, now one and now the other property comes to the front. In bacterial diseases affecting or being transmitted mostly by the blood, it is the toxins which act chiefly. The convenient term infection is applied to those conditions in which there has been a multiplication of living organisms after they have entered the body, the word intoxication indicating a condition of poisoning brought about by their products. It will be apparent at once that we may have both these conditions present, the former before the latter, and the latter following as a direct effect of the former. Until intoxication occurs there may be few or no symptoms, but directly enough bacteria are present to produce in the body certain poisons in sufficient amount to result in more or less marked tissue change, then the symptoms of that tissue change appear. This period of latency between infection and the appearance of the disease is known as the incubation period. Take typhoid, for example. A man drinks a typhoid-polluted water. For about fourteen days the bacilli are making headway in his body without his being aware of it. But at the end of that incubation period the signs of the disease assert themselves. Professor Watson Cheyne and others have maintained that there is some exact proportion between the number of bacteria gaining entrance and the length of the incubation period.
Speaking generally, we may note that pathogenic bacteria divide themselves into two groups: those which, on entering the body, pass at once, by the lymph or blood stream, to all parts of the body, and become more and more diffused throughout the blood and tissues, although in some cases they settle down in some spot remote from the point of entrance, and produce their chief lesions there. Tubercle and anthrax would be types of this group. On the other hand, there is a second group, which remain almost absolutely local, producing only little reaction around them, never passing through the body generally, and yet influencing the whole body eventually by means of their ferments or toxins. Of such the best representatives are tetanus and diphtheria. The local site of the bacteria is, in this case, the local manufactory of the disease.
Whilst the mere bodily presence of bacteria may have mechanical influence injurious to the tissues (as in the small peripheral capillaries in anthrax), or may in some way act as a foreign body and be a focus of inflammation (as in tubercle), the real disease-producing action of pathogenic bacteria depends upon the chemical poisons (toxins) formed directly or indirectly by them. Though within recent years a great deal of knowledge has been acquired about the formation of these bodies, their exact nature is not known. They are allied to albuminous bodies and proteoses, and are frequently described as tox-albumens. It may be found, after all, that they are not of a proteid nature. Sidney Martin has pointed out that there is much that is analogous between the production of toxins and the production of the bodies of digestion. Just as ferments are necessary in the intestine to bring about a change in the food by which the non-soluble albumens shall be made into soluble peptones and thus become absorbed through the intestinal wall, so also a ferment may be necessary to the production of toxins. Such ferments have not as yet been isolated, but their existence in diphtheria and tetanus is, as we have seen, extremely likely. However that may be, it is now more or less established that there are two kinds of toxic bodies, differing from each other in their resistance to heat. It may be that the one most easily destroyed by heat is a ferment and possibly an originator of the other. A second division which has been suggested for toxic bodies, and to which reference has been made, is intracellular and extracellular, according to whether or not the poison exists within or without the body of the bacillus.
Lastly, we may turn to consider the action of the toxins on the individual in whose body-fluids they are formed. It is hardly necessary to say that any action which bacteria or toxins may have will depend upon their virulence, in some measure upon their number, and not a little upon the channel of infection by which they have gained entrance. It could not be otherwise. If the virulence is attenuated, or if the invasion is very limited in numbers, it stands to reason that the pathogenic effects will be correspondingly small or absent. The influence of the toxins is twofold. In the first place (i.) they act locally upon the tissues at the site of their formation, or at distant points by absorption. There is inflammation with marked cell-proliferation, and this is, more or less rapidly, followed by a specific cell-poisoning. The former change may be accompanied by exudation, and simulate the early stages of abscess formation; the latter is the specific effect, and results, as in leprosy and tubercle, in infective nodules. The site in some diseases, like typhoid (intestinal ulceration, splenic and mesenteric change) or diphtheria (membrane in the throat), may be definite and always the same. But, on the other hand, the site may depend upon the point of entrance, as in tetanus. The distant effects of the toxin are due to absorption, but what controls its action it is impossible to say. We only know that we do find pathological conditions in certain organs at a distance and without the presence of bacteria. We have a parallel in the action of drugs; for example, a drug may be given by the mouth and yet produce a rash in some distant part of the body. In the second place (ii.) toxins produce toxic symptoms. Fever and many of the nervous conditions resulting from bacterial action must thus be classified. We have, it is true, the chemical symptoms of the pathological tissue change, for example, the large spleen of anthrax or the obstruction from diphtheritic membrane. But, in addition to these, we have general symptoms, as fever, in which after death no tissue change can be formed.
We may now consider briefly some of the more important types of disease produced by bacteria:
1. Tuberculosis.[90] As far back as 1794 Baillie drew attention to the grey miliary nodules occurring in tuberculous tissue which gave rise to the term "tubercles." This preliminary matter was confirmed by Bayle in 1810.
In 1834 Laennec described all caseous deposits as "tubercles," insisting upon four varieties:
(1) Miliary, which were about the size of millet seeds, and in groups;
(2) Crude, miliary tubercles in yellow masses;
(3) Granular, similar to the last, but scattered;
(4) Encysted, a hard mass of crude tubercle with a fibrous or semi-cartilaginous capsule.
The tubercle possesses in many cases a special structure, and certain cell-forms frequently occur in it and give it a characteristic appearance. The central part of the tubercle usually contains giant cells with numerous nuclei. The uninuclear cells are partly lymphoid, partly large epithelial or endothelial cells; these are called epithelioid cells.
It was not till 1865 that the specific nature of tuberculosis was asserted by Villemin. Burdon Sanderson (1868–69) in England confirmed his work, and it was extended by Connheim, who a few years later laid down the principle that all is tubercular which by transference to properly constituted animals is capable of inducing tuberculosis, and nothing is tubercular unless it has this capability.
Klebs (1877) and Max Schiller (1880) described masses of living cells or micrococci in many tuberculous nodules in the diseased synovial membrane and in lupus skin. In 1881 Toussaint declared he had cultivated from the blood of tubercular animals and from tubercles an organism which was evidently a micrococcus, and in the same year Aufrecht stated that the centre of a tubercle contained small micrococci, diplococci, and some rods. But it was not till the following year, 1882, that Koch discovered and demonstrated beyond question the specific Bacillus tuberculosis.
It is now held to be absolutely proved that the introduction of the bacillus, or its spores or products, is the one and only essential agent in the production of tuberculosis. Its recognised manifestations are as follows:
| Tuberculosis | in the lungs = acute or chronic phthisis; |
| " | in the skin = lupus[91]; |
| " | in the mesenteric glands = Tabes mesenterica; |
| " | in the brain = hydrocephalus; |
| " | in lymphatic glands = Scrofula.[91] |
The disease may occur generally throughout the body or locally in the suprarenal capsules, prostate, intestine, larynx, membranes of the heart, bones, ovaries, pleura, kidneys, spleen, testicles, Fallopian tubes, uterus, etc.
We may summarise the history of the pathology of tubercle thus:
1794. Baillie drew attention to grey miliary nodules occurring in tuberculosis, and called them "tubercles."
1834. Laennec described four varieties: miliary; crude; granular; encysted.
1843. Klencke produced tuberculosis by intravenous injection of tubercular giant cells.
1865. Villemin demonstrated infectivity of tubercular matter by inoculation of discharges; Connheim, Armanni, Burdon Sanderson, Wilson Fox, and others showed that nothing but tubercular matter could produce tuberculosis.
1877. Living cells were found in tubercles, "micrococci" (Klebs, Toussaint, Schiller).
1882. Koch isolated and described the specific bacillus, and obtained pure cultivations (1884).
The Bacillus of Koch, 1882. Delicate cylindrical rods, measuring 1.5–4 micromillimetres in length and about .2 µ in breadth; non-motile. Many are straight with rounded ends; others are slightly curved. They are usually solitary, but may occur in pairs, lying side by side or in small masses. They are chiefly found in fresh tubercles, more sparingly in older ones. Some lie within the giant cells; others lie outside; shorter in tissue sections of bovine tuberculosis, but longer in the milk (Crookshank).
When stained they appear to be composed of irregular cubical or spherical granules within a faintly stained sheath. In recent lesions the protoplasm appears more homogeneous, and takes on the segmented or beaded character only in old lesions, pus, or sputum.
Morphological differences are found under different circumstances, and within limits variation occurs according to the environment.
Cultivation on Various Media. Koch inoculated solid blood serum with tubercular matter from an infected lymphatic gland of a guinea-pig, and noticed the first signs of growth in ten or twelve days in the form of whitish, scaly patches. These enlarged and coalesced with neighbouring patches, forming white, roughened, irregular masses. Nocard and Roux showed that by adding 5/8 per cent. of glycerine to the media commonly used in the laboratory, such as nutrient agar or broth, the best growth is obtained.
On glycerine broth or glycerine agar abundant growth appears at the end of seven or eight days. By continuous sub-culture on glycerine agar the virulence of the bacillus is diminished. But in fifteen days after inoculation of the medium the culture equals in extent a culture of several weeks' age on blood serum.
Sub-cultures from glycerined media will grow in ordinary broth without glycerine (Nocard, Roux, Crookshank).
In alkaline broth to which a piece of boiled white of egg was added Klein obtained copious growths, and found that continued sub-culturing upon this medium also lessens the virulence.
Description of Cultivations:—On glycerine agar minute white colonies appear in about six days, raised and isolated, and coalescing as time advances, forming a white lichenous growth, fully developed in about two months.
On glycerine broth a copious film appears on the surface of the liquid, which if disturbed falls to the bottom of the flask as a deposit.
Spore Formation. In very old cultivations spore-like bodies can be observed both in stained and unstained preparations, but neither the irregular granules within the capsule nor the unstained spaces between the granules are spores (Babes and Crookshank). That the bacilli possess spores is believed on account of the following facts:
1. That tubercular sputum, when thoroughly dried, maintains its virulent character (Koch, Schill, Fischer, etc.). No sporeless bacillus is known which can survive through drying.
2. That tubercular matter and cultures survive temperature up to 100° C. Non-spore-bearing bacilli and micrococci are killed by being exposed for five minutes to a temperature of 65–70° C., whereas spores of other bacilli withstand much higher temperatures.
3. Tubercular sputum distributed in salt solution does not lose its virulence by being kept at 100° C. for one or two minutes; sporeless bacilli certainly would (Klein).
4. A solution of per-chloride of mercury does not kill the tubercle bacilli, as it does sporeless bacilli (Lingard and Klein).
Koch and many bacteriologists have declared the bacillus to be a "true parasite." Koch based this view upon the belief which he entertained that the bacillus can grow only between 30° C. and 41° C., and therefore in temperate zones is limited to the animal body and can originate only in an animal organism. "They are," he said, "true parasites, which cannot live without their hosts. They pass through the whole cycle of their existence in the body." But at length Koch and others overcame the difficulties and grew the bacillus as a saprophyte.
Schottelius[92] has observed that tubercle bacilli taken from the lung of phthisical persons buried for years still retains its virulence and capability of producing tuberculosis upon inoculation. He further shows that tubercular lung kept in soil (enclosed in a box) shows a marked rise in temperature. Klein quotes these experiments as indications that "tubercle bacilli are not true parasites, but belong to the ectogenic microbes which can live and thrive independent of a living host."
It has now been abundantly proved that the bacillus of tuberculosis is capable of accommodating itself to circumstances much less favourable than had been supposed, especially as regards temperature.
Temperature of Growth of Bacillus. 30–41° C. have been laid down by Koch as the limits of temperature at which the bacillus will grow in culture medium outside the body. The generally accepted temperatures as most favourable to the growth of the bacillus are between 36° C. and 38° C.
Sir Hugh Beevor, however, was able to grow the bacillus upon glycerine agar at 28° C. (82° F.), obtaining an ample culture which developed somewhat more slowly than on blood serum, and to a less extent than at 37° C. In both Beevor succeeded in growing the bacillus at a lower temperature even than on agar, viz., at a temperature rarely above 60° F. Sheridan Delépine and others have also been successful in obtaining growths at room temperature both in summer and winter.
Although, speaking generally, there is an actual cessation of growth at low temperature, the bacillus may be exposed to very low temperatures for a considerable time without losing its power of again becoming active when returned to a favourable environment (Woodhead).
The Relation of the Bacillus to the Disease. All four of Koch's postulates have been fulfilled in the case of Bacillus tuberculosis. Hence we are dealing with the specific cause of the disease. Yet, whilst this is so, we may usefully ask ourselves: How does the bacillus set up the changes in normal tissues which result in tubercular nodules? In arriving at a solution of this problem we are materially aided if we bear in mind the fact that such an organism in healthy tissues has a double effect. First, there is an ordinary inflammatory irritation, and secondly, there is a specific change set up by the toxins of the bacillus. Directly the invading bacilli find themselves in a favourable nidus they commence multiplication. In three or four days this acts as an irritant upon the surrounding connective-tissue cells, which proliferate, and become changed into large cells known as epithelioid cells. At the periphery of this collection of epithelioid cells we have a congested area. This change has been accomplished by the presence of the bacilli themselves. The production of their specific poisons changes the epithelioid cells in the centre of the nodule, some of which become fused together, whilst others expand and undergo division of nucleus. By this means we obtain a series of large multi-nucleated cells named giant cells. If the disease is very active, these soon caseate and break down in the centre. In a limb we get a discharge; in a lung we get an expectoration. Both discharge and expectoration arise from a breaking down of the new cell formation. Previously to breaking down we have in a fully developed nodule healthy tissue, inflammatory zone, epithelioid cells, giant cells, containing nuclei and bacilli. The sputum or the discharge will, during the acute stage of the disease at all events, contain countless numbers of the bacilli, which may thus be readily detected, and their presence used as evidence of the disease. It is obvious that if the centre of the nodule degenerates and comes away as discharge a cavity will be left behind. By degrees this small cavity may become a very large one, as is frequently the case in the lung, which particularly lends itself to such a condition. Hence, though at the outset a tubercular lung is solid, at the end it is hollow.
| Bacillus Tuberculosis (In sputum from a case of phthisis, "consumption" of the lungs) × 1000 By permission of the Scientific Press, Limited | Bacillus Tuberculosis (The bacilli are arranged within the giant cell) × 1000 |
| Streptococcus Pyogenes (From broth culture) × 1000 By permission of the Scientific Press, Limited | Bacillus Anthracis (From splenic blood of cow) × 1000 By permission of the Scientific Press, Limited |
The exact period of giant-cell formation depends on the rapidity of the formative processes. Thus different conditions occur. Inside the giant cells the bacilli are arranged in relation to the nuclei in one of three ways: (a) polar, (b) zonal, or (c) mixed. The breaking down of the nodule is partly due to the cell-poisons, and partly because the nodule is non-vascular, owing to the fact that new capillaries cannot grow into the dense nodule, and the old ones are all occluded by the growth of the nodule.
From the local foci of disease the tubercle process spreads chiefly by three channels:
(a) By the lymphatics, affecting particularly the glands. Thus we get tuberculosis set up in the bronchial, tracheal, mediastinal, and mesenteric glands, and it is so frequently present as to be a characteristic of the disease. This is the common method of dissemination in the body.
(b) By the blood-vessels, by means of which bacilli may be carried to distant organs.
(c) By continuity of tissues, infective giant-cell systems encroaching upon neighbouring tissues, or discharge from lungs or bronchial glands obtaining entrance to the gullet and thus setting up intestinal disease also.
It has been abundantly proved that the respiratory and digestive systems are principally affected by Koch's bacillus. Wherever the bacilli are arrested, they excite formation of granulations or miliary tubercular nodules, which increase and eventually coalesce. The lymphatic glands which collect the lymph from the affected region are the earliest affected, always the nearest first, and then the disease appears to be appreciably stopped on its invading march. Each lymphatic gland acts as a temporary barrier to progress until the disease has broken its structure down. It remains local, in spite of increase in number and importance of the foci of disease, as long as the bacilli have not gained access to the blood stream.
Toxins and Tuberculin. Koch, Crookshank, and Herroun, Hunter, and others have isolated products from pure cultures of the tubercle bacillus. These have comprised chiefly albumoses, alkaloids, and various extractives. Koch's observations led him to suppose that in pure cultures of tubercle a substance appeared having healing action on tuberculosis, and an extract of this in glycerine he termed "tuberculin." It was made as follows: A veal broth containing peptone and glycerine was inoculated with a pure culture of the bacillus and incubated at 38° C. for six or eight weeks. An abundant growth with copious film formation appeared. The culture was then concentrated by evaporation over a water-bath until reduced to about one-tenth of its volume.
Flask used in the Preparation of Tuberculin
The announcements in 1890 and 1891 to the effect that a "cure" had been discovered for consumption will be remembered. The hopes thus raised were unfortunately not to be realised. Koch advocated injections of this tuberculin in cases of skin tubercle (lupus) and consumptive cases. In many of these benefit was apparently derived, but its general application was not founded upon any substantial basis. Dead tissue, full of bacilli, could not thus be got rid of; nor could the career of the isolated bacilli distributed through the body be thus checked.
Tuberculin has, however, found a remarkable sphere of usefulness in causing reaction in animals suffering from tuberculosis. Indeed, tuberculin is the most valuable means of diagnosis that we possess (MacFadyen). When injected (dose, 30–40 centigrammes) it causes a rise of one and a half to three degrees. The fever begins between the twelfth and fifteenth hour after injection, and lasts several hours. The duration and intensity of the reaction have no relation to the number and gravity of the lesions, but the same dose injected into healthy cattle causes no appreciable febrile reaction. The tuberculous calf reacts just as well as the adult, but the dose is generally 10–20 centigrammes. Injections of tuberculin have no troublesome effect on the quantity or quality of the milk of cows or on the progress of gestation.
Tuberculosis of Animals. Cattle come first amongst animals liable to tubercle. Horses may be infected, but it is comparatively rare, and among small ruminants the disease is rarer still. Dogs, cats, and kittens may be easily infected. Amongst birds, fowls, pigeons, turkeys, and pheasants, the disease assumes almost an epidemic character. Especially do animals in confinement die of tubercle, as is illustrated in zoölogical gardens. Respecting the lesions of bovine tuberculosis, it will be sufficient to say that nothing is more variable than the localisation or form of its attacks. The lungs and lymphatic glands come first in order of frequency, next the serous membranes, then the liver and intestines, and lastly the spleen, joints, and udder (Nocard).
The anatomical changes in bovine tubercle are mostly found in the lungs and their membranes, the pleuræ. It also affects the internal membrane lining, the abdomen and its chief organs, the peritoneum, and the lymphatic glands. In both these localities a characteristic condition is set up by small grey nodules appearing, which increase in size, giving an appearance of "grapes." Hence the condition is called grape disease, or Perlsucht. The organs, as we have said, are equally affected, and when we add the lymphatic glands we have a fairly complete summary of the form of the disease as it occurs in cattle. As has been clearly pointed out by Martin, Woodhead, and others in their evidence before the Royal Commission, the organs, glands, and membranes are the sites for tubercle, not the muscles (or "meat"). This latter is most liable to convey infection when the butcher smears it with the knife which he has used to remove tubercular organs.
As regards the udder in its relation to milk infection, it may be desirable to state that the initial lesion, according to Nocard and Bang, takes the form of a progressive sclerosis. The interlobular connective tissue, normally scanty, becomes thickened, fibrous, and infiltrated by minute miliary granulations. The granular tissue is thus "smothered by the hypertrophy and fibrous transformation of the interstitial connective tissue" (Nocard). The walls of the ducts are thickened and infiltrated, the lumen frequently dilated by masses of yellow caseous material. On the whole it may be said that tubercle of the udder is rare. Usually only one quarter is attacked, and by preference the posterior. For some time the milk remains normal, but gradually it becomes serous and yellow, and contains coagula holding numbers of bacilli. Lastly, it becomes purulent and dries up altogether. While the milk is undergoing these changes the lesion of the udder is becoming more marked, the tissue becomes less supple, and the toughness increases almost to a wooden hardness.
The general anatomical characteristics of the disease are similar to those occurring in man.
The percentage of cattle suffering from tubercle varies. In Germany it appears to vary from 2 to 8 per cent. of all cattle, in Saxony 17 to 30 per cent., in England 22 per cent. approximately (in London 40 per cent.), in France 25 per cent. Lowland breeds are much more infected than mountain breeds, which possess stronger constitutions.
Tuberculosis of the pig is less common than that of cattle, but not so rare as that of the calf (Nocard). In nine out of ten cases the pig is infected by ingestion, particularly when fed on the refuse from dairies and cheese factories. The disease follows the same course as in cattle. The finding of the bacillus is difficult, and the only safe test is inoculation (Woodhead).
Sheep are very rarely tuberculous by nature, though there is evidence to believe that very long cohabitation with tuberculous cattle would succeed in transmitting tuberculosis to some sheep.
Tuberculosis in the horse is relatively very rare. It attacks the organs of the abdominal cavity, especially the glands; it affects the lung secondarily as a rule. The cases are generally isolated ones, even though the animal belongs to a stud. Nocard holds that the bacillus obtained from the pulmonary variety is like the human type, whilst the abdominal variety is more like the avian bacillus.
Nocard says[93]:
"If the dog can become tuberculous from contact with man, the converse is equally true. Infection is at any rate possible when a house-dog scatters on the floor, carpet, or bed, during its fit of coughing, virulent material, which is rendered extremely dangerous by drying, especially for children, its habitual playmates. The most elementary prudence would recommend the banishment from a room of every dog which coughs frequently, even though it only seems to be suffering from some common affection of the bronchi or lung."
Tuberculosis is a common disease among the birds of the poultry-yard: poultry, pigeons, turkeys, pea-fowl, guinea-fowl, etc. They are infected almost exclusively through the digestive tract, generally by devouring infected secretions of previous tubercular fowls. Whatever the position or form of avian tuberculosis, the bacilli are present in enormous numbers, and are often much shorter and sometimes much longer than those met with in tuberculous mammalia, and grow outside the body at a higher temperature (43° C.). They are also said to be more resistant and of quicker growth. The species is probably identical with Koch's bacillus, though there are differences. In the nodule, which is larger than in human tuberculosis, there are few or no giant cells, and it does not so readily break down.
Nocard and others have demonstrated the fact that the Bacillus tuberculosis of Koch is the common denominator in all tubercular disease, whatever and wherever its manifestations, in all animals. The bacillus, they hold, may, however, experience profound modifications by means of successive passages through the bodies of divers species of animals. But if the modifications which it undergoes as a result of transmissions through birds, for example, are profound enough to make the bacillus of avian tubercle a peculiar variety of Koch's bacillus, they are not enough, it is generally believed, to make these bacilli two distinct species.
We may, therefore, take it for granted that tuberculosis is one and the same disease, with various manifestations, common to man and animals, intercommunicable, and having but one vera causa: the Bacillus tuberculosis of Koch.
The Prevention of Tuberculosis. At the present time much attention is being directed to the administrative personal control of tuberculosis. How greatly this is needed in so preventable a disease is evident from a perusal of the following quotation from the Registrar-General's reports. (See opposite page.)
These figures show a marked decline in the three worst forms of the disease. But this decline is apparently less marked in tabes than in phthisis or tubercular meningitis, i. e., less in the kind of tubercle due to the ingestion of infected milk. Fortunately the State is beginning to realise its duty in regard to preventive measures. The abolition of private slaughter-houses, the protection of meat and milk supplies, the seizure of tuberculous milch cows, and such like measures fall obviously within the jurisdiction of the State rather than the individual, and claim the earnest and urgent attention of the public health departments of states.[94]
ENGLISH DEATH-RATES FROM ALL TUBERCULAR DISEASES
THE FOLLOWING IS A TABLE OF DEATH-RATES TO A MILLION LIVING (ENGLAND), 1877–1897 (Reg.-Gen. Annual Reports):—
| 1877 | 1878 | 1879 | 1880 | 1881 | 1882 | 1883 | 1884 | 1885 | 1886 | 1887 | |
| Tabes Mesenterica | 316 | 348 | 300 | 370 | 284 | 313 | 289 | 310 | 251 | 300 | 253 |
| Tubercular Meningitis | 319 | 338 | 322 | 330 | 276 | 264 | 262 | 264 | 253 | 257 | 236 |
| Phthisis | 2079 | 2111 | 2021 | 1869 | 1825 | 1850 | 1880 | 1827 | 1770 | 1739 | 1615 |
| Other Forms | 126 | 124 | 116 | 129 | 145 | 153 | 160 | 170 | 157 | 177 | 179 |
| Total | 2840 | 2921 | 2759 | 2698 | 2530 | 2580 | 2591 | 2571 | 2431 | 2473 | 2283 |
| 1888 | 1889 | 1890 | 1891 | 1892 | 1893 | 1894 | 1895 | 1896 | 1897 | |
| Tabes Mesenterica | 240 | 269 | 265 | 251 | 242 | 265 | 192 | 243 | 196 | 201 |
| Tubercular Meningitis | 239 | 234 | 240 | 247 | 227 | 226 | 211 | 222 | 210 | 213 |
| Phthisis | 1568 | 1573 | 1682 | 1599 | 1468 | 1468 | 1385 | 1398 | 1307 | 1341 |
| Other Forms | 174 | 183 | 189 | 203 | 199 | 186 | 185 | 200 | 179 | 175 |
| Total | 2221 | 2259 | 2376 | 2300 | 2136 | 2145 | 1973 | 2063 | 1892 | 1930 |
Tabes mesenterica is tuberculosis of the alimentary canal and mesenteric lymph glands.
Tubercular meningitis is the name of the same disease as it affects the membranes of the brain (acute hydrocephalus).
Phthisis is the term applied to "consumption," or tubercle in the lungs.
But personal hygiene and the prevention of the transmission of the disease depend very largely indeed upon the mass of the population. Hence we hail with satisfaction the recent endeavours to educate public opinion. In order to make this matter very simple indeed, we have placed in a footnote a series of statements embodying some of the chief facts which every individual in our crowded communities should know.[95]
Bacillus of Diphtheria
Diphtheria (Klebs-Löffler Bacillus, 1882–1884). Diphtheria is an infective disease characterised by a variety of clinical symptoms, but commonly by a severe inflammation followed by a fibrous infiltration (constituting a membrane) of certain parts. The membrane ultimately breaks down. The parts affected are the mucous membrane of the fauces, larynx, pharynx, trachea, and sometimes wounds and the inner wall of the stomach. The common sign of the disease is the membrane in the throat; but muscle weakness, syncope, albuminuria, post-diphtheritic paralysis, convulsions, and many other symptoms guide the physician in diagnosis and the course of the disease.
The Bacillus diphtheriæ was isolated from the many bacteria found in the membrane by Löffler. Klebs had previously identified the bacillus as the cause of the disease. It is a slender rod, straight or slightly curved, and remarkable for its beaded appearance; there are also irregular and club-shaped forms. It differs in size according to its culture medium, but is generally 3 or 4 µ in length. In the membrane which is its strictly local habitat in the body—indeed, the bacillus is found nowhere else in the body—it almost invariably shows parallel grouping, lying between the fibrin of the membrane, and most largely in its deeper parts. Here it is mixed with other bacilli, micrococci, staphylococci, and streptococci, all of which are present and performing their part in complicating the disease. The bacillus possesses five negative characters; namely, it has no spores, threads, or power of mobility, and does not produce liquefaction or gas. It stains with Löffler's methylene blue, and shows metachromatic granules and polar staining. Its favourable temperature is blood-heat, though it will grow at room temperature. It is aërobic, and, indeed, prefers a current of air. Löffler contrived a medium for cultivation which has proved most successful. It is made by mixing three parts of ox-blood serum with one part of broth containing 1 per cent. of glucose, 1 per cent. of peptone, and 1/2 per cent. of common salt; the whole is coagulated. Upon this medium the Klebs-Löffler bacillus grows rapidly in eighteen or twenty hours, producing scattered "nucleated" round white colonies, becoming yellowish. It grows well in broth, but without producing either a pellicle or turbidity; it can grow on the ordinary media, though its growth on potato is not visible; on the white of egg it flourishes extremely well.
It retains its vitality in cultures and sometimes in the throat for months. Three or four weeks is the average length of time for its existence in the membrane, but, owing to the difficulty of killing it in situ, it may live on for as long as a year. All the conditions in the throat—mucous membrane, blood-heat, moisture, air—are extremely favourable to the bacillus; but it is very materially modified in virulence. It is secured for diagnostic purposes by one of two methods: (a) Either a piece of the membrane is detached, and after washing carefully examined by culture as well as the microscope; or (b) a "swab" is made from the infected throat and cultured on serum, and incubated at 37° C. for eighteen hours and then microscopically examined. Both methods—and there is no further choice—present some difficulties owing to the large number of bacteria found in the throat. Hence a negative result must be accepted with reserve.
We have already referred at some length to the question of toxins in diphtheria, and need not dwell further upon that matter. Still a word or two may be said here summarising the general action of the bacillus. Locally it produces inflammatory change with fibrinous exudation and some cellular necrosis. In the membrane a ferment is probably produced which, unlike the localised bacilli, passes throughout the body and by digestion of the proteids produces albumoses and an organic acid which have the toxic influence. The toxins act on the blood-vessels, and nerves, and muscle fibres of the heart, and many of the more highly specialised cells of the body. Thus we get degenerative changes in the kidney, in cells of the central nervous system, in the peripheral nerves (post-diphtheritic paralysis), and elsewhere, these pathological conditions setting up, in addition to the membrane, the signs of the disease. The bacillus is pathogenic for the horse, ox, rabbit, guinea-pig, cat, and some birds. Cases are on record of supposed infection of children by cats suffering from the disease. The horse, it will be remembered, yields the antitoxin which has saved so many lives (Metropolitan Asylums Board Report, 1896).
The influence of drainage, milk, and schools must not be forgotten by sanitary authorities any more than the essential importance of adequate isolation hospital accommodation. Mr. Shattock's experiments on the effect of sewer air upon attenuated Klebs-Löffler bacilli have been mentioned (see p. 105). Nevertheless there can be no doubt that emanations from defective drains have a materially predisposing effect, not, it is true, upon the bacilli, but upon the tissues. Sore throats thus acquired are par excellence the site for the development of diphtheria.
The influence of school attendance has claimed the recent attention of the Medical Officer of the London School Board and the Medical Officer of the administrative County of London. In London since 1881 there has been a marked increase of diphtheria, which has occurred, though in a much less degree, throughout England and Wales.
The Registrar-General has only classified diphtheria as a separate disease since 1855, when the death-rate per 1,000,000 in England and Wales was stated as 20. The following are the figures for four decades up to 1895:
AVERAGE DEATH-RATE PER MILLION OF THE POPULATION FROM DIPHTHERIA IN ENGLAND AND WALES AND IN LONDON (IN DECADES 1856–95)
| England and Wales | London. | |
| 1856–65 | 246.9 | 225.4 |
| 1865–75 | 124.8 | 123.5 |
| 1875–85 | 129.0 | 176.7 |
| 1885–95 | 210.6 | 421.4 |
From these figures the extraordinary increase during the last few years is clearly demonstrated.
Sir Richard Thorne Thorne, in 1891, drew attention to the influence of damp soils and schools upon diphtheria. In 1894 Mr. Shirley Murphy, Medical Officer to the London County Council, reported that there had been an increase in diphtheria mortality in London at school ages (three to ten) as compared with other ages since the Elementary Education Act became operative in 1871; that the increased mortality from diphtheria in populous districts, as compared with rural districts, since 1871, might be due to the greater effect of the Education Act in the former; and that there was a diminution of diphtheria in London during the summer holidays at the schools in 1893, but that 1892 did not show any marked changes for August.
In 1896 Professor W. R. Smith, the Medical Officer to the London School Board, furnished a report[96] on this same subject of school influence, in which he produces evidence to show that the recrudescence of the disease in 1881–90 was greatest in England and Wales at the age of two to three years, and in London at the age of one to two years, in both cases before school age; that age as an absolute factor in the incidence of the disease is enormously more active than any school influence, and that personal contact is another important source of infection.
Although it is said that "statistics can be made to prove anything," there can be little doubt that both of these reports contain a great deal of truth; nor are these truths incompatible with each other. They both emphasise age as a great factor in the incidence of the disease, and whatever affects the health of the child population, like schools, must play, directly or indirectly, a not unimportant part in the transmission of the disease.
The Pseudo-diphtheria Bacillus.[97] Löffler and Hoffman described a bacillus having the same morphological characters as the true Bacillus diphtheriæ, except that it had no virulence. Roux believes this is merely an attenuated diphtheria bacillus. It is frequently found in healthy throats. The chief differences between the real and the pseudo-bacillus are:
1. The pseudo-bacillus is thicker in the middle than at the poles, and not so variable as the Bacillus diphtheriæ. Polar staining is absent.
2. Its growth on potato reveals cream-coloured colonies visible in a couple of days; the real bacillus is invisible.
3. The pseudo-bacillus will not grow at all anaërobically in hydrogen, but the Bacillus diphtheriæ is able to do so.
4. There is the great difference in virulence.
Suppuration. This term is used to designate that general breaking down of cells which follows acute inflammation. An "abscess" or "gathering" is a collection, greater or smaller, of the products of suppuration. The word pus is generally used to describe this matter. We may have such an advanced inflammatory condition in any locality of the body, and it will assume different characters according to its site. Hence there are connected with suppuration, as causal agents, a variety of bacteria. Pus is not matter containing a pure culture of any specific species, but, on the contrary, is generally filled with a large number of different species. The most important are as follows:
1. Staphylococcus pyogenes aureus. These are micrococci arranged in groups, which have been likened to bunches of grapes. They are the common organisms found in pus, and were with other auxiliary bacteria first distinguished as such by Professor Ogston, of Aberdeen. There are several forms of the same species, differing from each other in colour.
Thus we have the S. pyogenes aureus (golden yellow), albus (white), citreus (lemon), and others. They occur commonly in nature, in air, soil, water, on the surface of the skin, and in all suppurative conditions. The aureus is the only one credited with much virulence. It occurs in the blood in blood-poisoning (septicæmia, pyæmia), and is present in all ulcerative conditions, including ulcerative disease of the valves of the heart.
The Staphylococcus cereus albus and S. cereus flavus are slightly modified forms of the S. pyogenes aureus, and are differentiated from it by being non-liquefying. They produce a wax-like growth on gelatine.
Staphylococcus pyogenes aureus, the type of the family, is grown in all ordinary media at room temperature, though more rapidly at 37° C. Liquefaction sets in at a comparatively early date, and subsequently we have in the gelatine test-tube cultures a flocculent deposit of a bright yellow amorphous mass, and in gelatine plates small depressions of liquefaction with a yellow deposit. It renders all media acid, and coagulates milk. Its thermal death-point in gelatine is 58° C. for ten minutes, but when dry considerably higher. It is a non-motile and a facultative anaërobe; but the presence of oxygen is necessary for a bright colour. Its virulence readily declines.
2. Streptococcus pyogenes. In this species of micrococcus the elements are arranged in chains. Most of the streptococci in pus, from different sources, are one species, having approximately the same morphological and biological characters. Their different effects are due to different degrees of toxic virulence; they are always more virulent when associated with other bacteria, for example, the Proteus family.
The chains vary in length, consisting of more elements when cultured in fluid media. They multiply by direct division of the individual elements, and in old cultures it has been observed that the cocci vary in form and size. This latter fact gave support to the theory that streptococcus reproduced itself by arthrospores, or "mother-cells."
Types of Streptococcus
In culture upon the ordinary media streptococcus is comparatively slow-growing, producing minute white colonies on or about the sixth day. It does not liquefy gelatine, and remains strictly localised to the track of the inoculating needle. Like the staphylococcus, it readily loses virulence. The thermal death-point is, however, lower: 54° C. for ten minutes. Marmorek has devised a method by which the virulence may be greatly increased, and he holds that it depends upon the degree of virulence possessed by any particular streptococcus as to what effects it will produce. By the adoption of Marmorek's methods attempts have been made to prepare an antitoxin.
Streptococcus pyogenes has been isolated from the membrane of diphtheria, and from small-pox, scarlet fever, vaccinia, and other diseases. In such cases it is not the causal agent, but merely associated with the complications of these diseases. Suppuration and erysipelas are the only pathological conditions in which the causal agency of streptococcus has been sufficiently established.
3. The Bacillus pyocyaneus occurs in green pus, and is the cause of that colouration. Gessard was the first to prove its significance, and he describes two varieties.
Micrococcus Tetragonus
It is a minute, actively motile, non-sporulating bacillus, which occasionally complicates suppuration and produces green pus. Oxygen is necessary for pigmentation, which is due to two substances: pyocyanin, a greenish-blue product extracted with chloroform, and pyoxanthose, a brown substance derived from the oxidation of the former pigment. Both these colours are produced in cultivation outside the body. On gelatine the colour is green, passing on to olive. There is liquefaction. On potato we generally obtain a brown growth (compare Bacillus coli, B. mallei, and others). The organism grows rapidly on all the ordinary media, which it has a tendency to colour throughout.
It will be remembered that when speaking of the antagonism of organisms, we referred to the inimical action of Bacillus pyocyaneus upon anthrax.
4. Micrococcus Tetragonus. This species occurs in phthisical cavities and in certain suppurations in the region of the face. It is a micrococcus usually in the form of small tetrads. A capsule is always present and sometimes discernible.
5. Bacillus coli communis and many putrefactive germs commonly occur in suppurative conditions, but they are not restricted to such disorders (see p. 64).
Diplococcus of Neisser
6. Micrococcus gonorrhœæ (Neisser, 1879). This organism is more frequently spoken of as a diplococcus. It occurs at the acute stage of the disease, but is not readily differentiated from other similar diplococci except by technical laboratory methods. Each element presents a straight or concave surface to its fellow. A very marked concavity indicates commencing fission. The position which these diplococci take up in pus is intracellular, and arranged more or less definitely around the nucleus. Difficulty has often been found in cultivating this organism in artificial media outside the body. Wertheim and others have suggested special formulæ for the preparation of suitable media, but it is a very simple matter to secure cultures on agar plates smeared with human blood from a pricked finger. The plate is incubated at 37° C. At the end of twenty-four hours small raised grey colonies appear, which at the end of about four days show adult growth. The margin is uneven, and the centre more opaque than the rest of the colony. This diplococcus is readily killed, and sub-cultures must be frequently made to retain vitality and virulence. Light, desiccation, and a temperature of 55° C. all act germicidally. The organism stains readily in Löffler's blue, but is decolourised by Gram's method. It is more or less strictly parasitic to man. Its shape, size, character of growth, and staining properties assist in differentiating it from various similar diplococci.[98]
Anthrax. This disease was one of the first in which the causal agency of bacteria was proved. In 1849 Pollender found an innumerable number of small rods in the blood of animals suffering from anthrax. In 1863 Davaine described these, and attributed the disease to them. But it was not till 1876 that Koch finally settled the matter by isolating the bacilli in pure culture and describing their biological characters.
It is owing in part to its interesting bacterial history, which opened up so much new ground in this comparatively new science, that anthrax has assumed such an important place in pathology. But for other reasons, too, it claims attention. It appears to have been known in the time of Moses, and was perhaps the disease described by Homer in the First Book of the Iliad. Rome was visited by it in 740 B.C.
Anthrax is an acute disease, affecting sheep, cattle, horses, goats, deer, and man. Cats, white rats, and Algerian sheep are immune. Swine become infected by feeding on the offal of diseased cattle (Crookshank).
The post-mortem signs are mainly three: The spleen is greatly enlarged and congested, is friable to the touch, and contains enormous numbers of bacilli; the skin may show exudations forming dark gelatinous tumours; and the blood remains fluid for some time after death, is black, tar-like, contains bubbles of air, and shows other degenerative changes in the red corpuscles, whilst the small blood-vessels contain such vast quantities of bacilli that they may be ruptured by them. Particularly is this true in the peripheral arteries. Many of the organs of the body show marked congestion.
| Bacillus of Anthrax and Blood Corpuscles | Threads of Bacillus Anthracis, Showing Spores |
Clinically there is rise of temperature and rapid loss of muscular power. The bacilli of anthrax are square-ended rods 1 µ broad and 4–5 µ long. In the tissues of the body they follow the lines of the capillaries, and are irregularly situated. In places they are so densely packed as to form obstructions to the onward flow of blood. In cultures they are in chains end to end, having as a rule equal interbacillary spaces. In cultures long filaments and threads occur. The exact shape of the bacillus depends, however, upon two things: the staining and spore formation. Both these factors may very materially modify the normal shape. The spores of anthrax are oval endospores, produced only in the presence of free oxygen, and at any temperature between 18 and 41° C. On account of requiring free oxygen, they are formed only outside the body. The homogeneous protoplasm of the bacillus becomes granular; the granules coalesce, and we have spores. Each spore possesses a thick capsule, which enables it to resist many physical conditions which kill the bacillus. When the spore is ripe or has exhausted the parent bacillus, it may take on a resting stage, or under favourable circumstances commence germination, very much after the manner of a seed. The spores may infect a farm for many months; indeed, cases are on record which appear to prove that the disease on a farm in the autumn may by means of the spores be carried on by the hay of the following summer into a second winter. Thus, by means of the spores, the infection of anthrax may cling to the land for very long periods, even for years. Spores of anthrax can withstand 5 per cent. carbolic acid or 1–1000 corrosive sublimate for more than an hour; even boiling does not kill them at once, whilst the bacilli without their spores are killed at 54° C. in ten minutes. When the spores are dry they are much more resistant than when moist. Hence the persistence of the anthrax bacillus is due to its spores.
The bacillus is aërobic, non-motile, and liquefying. Broth cultures become turbid in thirty-six hours, with nebulous masses of threads matted together. The pellicle which forms on the surface affords an ideal place for spore formation.
Cultures in the depth of gelatine show a most characteristic growth. From the line of inoculation delicate threads and fibrillæ extend outwards horizontally into the medium. Liquefaction commences at the top, and eventually extends throughout the tube. On gelatine plates small colonies appear in thirty-six hours, and on the second or third day they look, under a low power of the microscope, like matted hair. The colonies after a time sink in the gelatine, owing to liquefaction. On potato, agar, and blood serum anthrax grows well.
Channels of Infection. 1. The Alimentary Canal. This is the usual mode of infection in animals grazing on infected pasture land. A soil suitable for the propagation of anthrax is one containing abundance of air and proteid material. Feeding on bacilli alone would probably not produce the disease, owing to the germicidal effect of the gastric juice. But spores can readily pass uninjured through the stomach and produce anthrax in the blood. Infected water as well as fodder may convey the disease. Water becomes infected by bodies of animals dead of anthrax, or, as was the case once at least in the south-west of England, by a stream passing through the washing-yard of an infected tannery. Manure on fields, litter in stalls, and infected earth may all contribute to the transmission of the disease. Darwin pointed out the services which are performed in superficial soils by earthworms bringing up casts; Pasteur was of opinion that in this way earthworms were responsible for continually bringing up the spores of anthrax from buried corpses to the surface, where they would reinfect cattle. Koch disputed this, but more recently Bollinger has demonstrated the correctness of Pasteur's views by isolating anthrax contagium from five per cent. of the worms sent him from an anthrax pasture. Bollinger also maintains that flies and other insects may convey the disease from discharges or carcasses round which they congregate.
Alimentary infection in man is a rare form, and it reveals itself in a primary diseased state known as mycosis intestinalis, an inflamed condition of the intestine and mesenteric lymph glands.
2. Through the Skin. Cutaneous anthrax goes by the name of malignant pustule, and is caused by infective anthrax matter gaining entrance through abrasions or ulcers in the skin. This local form is obviously most contracted by those whose occupation leads them to handle hides or other anthrax material (butchers and cleaners of hides). Two or three days after inoculation a red pimple appears, which rapidly passes through a vesicular stage until it is a pustule. Concomitantly we have glandular enlargement, general malaise, and a high temperature. Thus from a local sore a general infection may result. Unless this does occur, the issue will not be fatal, and the bacilli will never gain entrance into the blood or be anything but local.
3. Respiratory Tract. In man this is the commonest form of all, and is well known under the term "wool-sorters' disease," or pulmonary anthrax. This mode of infection occurs when dried spores are inhaled in processes of skin-cleaning. It frequently commences as a local lesion affecting the mucous membrane of the trachea or bronchi, but it rapidly spreads, affecting the neighbouring glands, which become greatly enlarged, and extending to the pleura and lung itself. Such cases, as a rule, rapidly end fatally.
From what has been said, it will be clear that anthrax carcasses are better not opened and exposed to free oxygen. An extended post-mortem examination is not necessary. Burning the entire carcass in a crematorium would be the ideal treatment. As such is not generally feasible the next best thing is to bury the carcass deeply with lime below and above it, and rail in the area to prevent other animals grazing off it.
A very small prick will extract enough blood to examine for the anthrax bacilli which are driven by the force of the blood-current to the small surface capillaries. This occurs, of course, only when the disease has become quite general, for in the early stage the healthy blood limits the bacilli to the internal organs. In such cases examination of the blood of the spleen is necessary.
Anthrax covers a wide geographical area all over the world, and no country seems altogether exempt. In Germany as many as 3700 animals have been lost in a single year. About 900 animals were attacked in 1897 in Great Britain.
Plague. This disease, like anthrax and leprosy, has a long historical record behind it. As the Black Death it decimated the population of England in the fourteenth century, and visited the country again in epidemic form in the middle of the seventeenth century, when it was called the Great Plague. Now, it is highly probable that these two scourges and the recent epidemic in the East are all forms of one and the same disease. As a matter of fact, it is difficult to be sure what was the exact pathology of a number of the grievous ailments which troubled our country in the Middle Ages, but from all accounts bubonic plague and true leprosy were amongst them. The former came and went spasmodically, as is its habit; the latter dragged through the length of several centuries.
Bacillus of Plague
The distribution of plague at the present time is fortunately a somewhat limited one, namely, a definite area in Asia known as the "Plague Belt." From Mesopotamia, as a sort of focus, the disease spreads northwards to the Caspian Sea, westwards to the Red Sea, southwards as far as Central India, and eastwards as far as the China Sea. This constitutes the "belt," but the disease may take an epidemic form, and is readily, though very slowly, conveyed by infection or contagion. It appears to be infectious by means of infective dust, and contagious by prolonged and intimate contact with the plague-stricken. Rats have been accused of conveying the disease from port to port, and even infecting man. It is clear that rats are not the only agency acting in this way. Nevertheless it is true that rats contract the disease more readily than any other animals, and that when suffering from it they may spread the infection. How it is thus spread it is not known. Drs. Cantlie and Yersin have pointed out that previously to an epidemic of plague rats die in enormous numbers.
The bacteriology of plague is almost the latest addition to the science. Kitasato, of Tokio, demonstrated the cause of plague to be a bacillus during the Hong Kong epidemic in 1894. This was immediately confirmed by Yersin, and further proved by the isolation in artificial media of a pure culture of a bacillus able to cause the specific disease of bubonic plague.
The bacillus was first detected in the blood of patients suffering from the disease. It takes the form of a small, round-ended, oval cell, with marked polar staining, and hence having an appearance not unlike a diplococcus. In the middle there is a clear interspace, and the whole is surrounded with a thick capsule, stained only with difficulty. The organisms are often linked together in pairs or even chains, and exhibit involution forms. In culture the bacillus is even more coccal in form than in the body.
The plague bacillus grows readily on the ordinary media at blood-heat, producing circular cream-coloured colonies with a wavy outline, which eventually coalesce to form a greyish film. The following negative characters help to distinguish it: No growth occurs on potato, milk is not coagulated, and gelatine is not liquefied; Gram's method does not stain the bacillus, and there are no spores; the bacillus is readily killed by heat and by desiccation over sulphuric acid at 30° C. Both in cultures and outside the body the bacillus loses virulence. To this may be attributed possibly the variety of forms of the plague bacillus which differ in virulence. On gaining entrance to the human body the bacillus affects in particular two organs, the spleen and the lymph glands. The latter become inflamed in groups, commencing frequently with those in the armpit (axillary) or groin (inguinal). The spleen suffers from inflammatory swelling, which may affect other organs also. In both places the bacilli occur in enormous numbers. Kitasato considers that the bacillus may enter the body by the three channels adopted by anthrax, namely, the skin, alimentary canal, and respiratory tract.
Haffkine has prepared a vaccine to be used as a prophylactic. He grows a pure culture of Kitasato's bacillus in broth upon the surface of which some globules of fat ("ghee") have been placed. The bacillus grows upon this fat in copious stalactite form. From time to time this growth is shaken down, until after five or six weeks the shaken broth appears milky. The contained bacilli are killed by heating the fluid to 70° C. for one hour. The resultant is the vaccine, of which the dose is 3 cc. Haffkine believes that inoculated persons in India have suffered twenty times less than non-inoculated living under the same conditions.
Plague is essentially a "filth disease," and it is frequently preceded by famine. Temperature and overcrowding exert an influence upon it. The areas affected by the disease in the Middle Ages, in the seventeenth century, and in 1894–96 are alike in being characterised by filth and overcrowding. There is little fear, speaking generally, of the plague ever flourishing under Western civilisation, where the conditions are such that even when it appears there is little to encourage or favour its development.
Leprosy. This ancient disease is said to have existed in Egypt 3500 B.C., and was comparatively common in India, China, and even in parts of Europe 500 B.C. We know it has existed in many parts of the world in the past, in which regions it is now extinct. Some of the earliest notices we have of it in this country come from Ireland, and date back to the fifth and sixth centuries. Even at that period of time also various classical descriptions of the disease had been written and various decrees made by the Church councils to protect lepers and prevent the spread of the disease, which was often looked upon as a divine visitation. In the tenth century leprosy was prevalent in England; it reached its zenith in the thirteenth century, or possibly a little earlier, and declined from that date to its extinction in the sixteenth. But even two hundred years later leprosy was endemic in the Shetlands, and it is recorded that in 1742 there was held a public thanksgiving in Shetland on account of the disappearance of leprosy.
At one time or another there were as many as two hundred institutions in the British Isles for the more or less exclusive use of lepers. Many of these establishments were of an ecclesiastical or municipal character, and probably the exact diagnosis of diseases was a somewhat lax matter. Bury St. Edmunds, Bristol, Canterbury, London, Lynn, Norwich, Thetford, and York were centres for lepers. Burton Lazars and Sherburn, in Durham, were two of the more famous leper institutions.
At the present time the distribution of the disease is mostly Asiatic. Norway contains about 1200 lepers, Spain approximately the same number. Scattered through Europe are perhaps another 600 or 700, in India 100,000, and a large number in Japan. The Cape possesses a famous leper hospital on Robben Island, with a number of patients. The disease is also endemic in the Sandwich Islands.
Descriptions of the pathological varieties of leprosy have been very diverse. The classification now generally adopted includes three forms: the tuberculated, the anæsthetic (or maculo-anæsthetic), and the mixed. Lepra tuberculosa is that form of the disease affecting chiefly the skin, and resulting in nodular tuberculated growth or a diffuse infiltration. It causes great disfigurement. The anæsthetic form causes a destruction of the nerve fibres, and so produces anæsthesia, paralysis, and what are called "trophic" changes. Not infrequently patches occur on the skin, which appear like parchment, owing to this trophic change. Bullæ may arise. When the tissue change is radical or far advanced, considerable distortion may result. The mixed variety of leprosy, as its name implies, is a mixture of the two other forms.
The Bacillus lepræ was discovered by Hansen in 1874. He found it in the lepra cells in the skin, lymph glands, liver, spleen, and thickened parts of the nerves. It is common in the discharges from the wounds of lepers. It is conveyed in the body by the lymph stream, and has rarely been isolated from the blood (Köbner).
| Bacillus of Plague (B. Pestis Bubonicæ) (From liver of rat) × 1000 By permission of the Scientific Press, Limited | Bacillus of Leprosy (Hansen) (From the tissues of a leper) × 1000 |
| Streptothrix Actinomyces (Ray Fungus) × 700 | Bacillus Mallei (Glanders) × 1000 |
The bacillus is present in enormous numbers in the skin and tissues, and has a form very similar indeed to Bacillus tuberculosis. It is a straight rod, and showing with some staining methods marked beading, but with others no beading at all. It measures 4 µ long and 1 µ broad. Young leprosy bacilli are said to be motile, but old ones are not. Neisser has maintained that the bacillus possesses a capsule and spores. The latter have not been seen, but Neisser holds that this is the form in which the bacillus gains entrance to the body. There is a characteristic which fortunately aids us in the diagnosis of this disease in the tissues, and that is the arrangement of the bacilli, which are rarely scattered or isolated, but gathered together in clumps and colonies. Bordoni-Uffreduzzi and Campania claim to have isolated the bacillus and grown it on artificial media, the former aërobically on peptone-glycerine-blood-serum, at 37° C., the latter anaërobically. But no other worker has been able to do this. Hence we are not able to study the bacteriology of leprosy at all completely, nor have inoculation experiments proved successful. Nevertheless there is little doubt that leprosy is a bacterial disease produced by the bacillus of Hansen. Bordoni-Uffreduzzi maintains that the parasitic existence of the Bacillus lepræ may alternate with a saprophytic stage. This may be of importance in the spread of the disease. There is evidence in support of the non-communicability of the disease by heredity or contagion. Segregation does not appear always to result in a decline of the disease, as we should expect if it were purely contagious. Ehlers, of Copenhagen, has, however, as recently as 1897, reaffirmed his belief in the contagiousness of leprosy; Virchow, on the other hand, has declared that it is not highly contagious. There is evidence to show that persons far advanced in the disease may live in a healthy community and yet not infect their immediate neighbours. Indeed, the transmission of the disease is still an unsolved problem. Mr. Hutchinson suggests diet, particularly uncooked or putrid fish, as a likely channel; on the other hand, leprosy appears in districts where no fish is eaten. Deficiency of salt, telluric and climatic conditions, racial tendencies, social status, poverty, insanitation, drinking water, even vaccination, have all secured support from various seekers after the true channel by which the bacillus gains entrance to the human body. The real mode of transmission is, however, still unknown. The decline and final extinction of leprosy in the British Islands was probably due in part to the natural tendency of the disease, under favourable hygienic circumstances, to die out, and in part to a general and extensive social improvement in the life of the people, to a complete change in the poor and insufficient diet, and to agricultural advancement, improved sanitation, and land drainage.
At the Leprosy Congress held in Berlin in 1897, Hansen again emphasised his belief that segregation was the cause of the decline of leprosy wherever it had occurred. But there appears to be some evidence to show that leprosy has declined where there has been no segregation whatever, and therefore, however favourable to decline such isolation may be, it would seem not to be actually necessary to the decline. At the same Congress Besnier declared in favour of the infective virus being widely propagated by means of the nasal secretion. Sticker states that the nasal secretion contains millions of lepra bacilli, especially in the acute stage of the disease, and Besnier and Sticker have pointed out how frequently and severely the septum nasi and skin over the nose are affected in leprosy. Several leprologists in India have recorded similar observations. These facts appear to support Besnier's contention that the disease is spread by nasal secretion.
We may fitly add here the conclusions arrived at by the English Leprosy Commission[99] in India:
"1. Leprosy is a disease sui generis; it is not a form of syphilis or tuberculosis, but has striking etiological analogies with the latter.
"2. Leprosy is not diffused by hereditary transmission, and, for this reason and the established amount of sterility among lepers, the disease has a natural tendency to die out.
"3. Though in a scientific classification of diseases leprosy must be regarded as contagious, and also inoculable, yet the extent to which it is propagated by these means is exceedingly small.
"4. Leprosy is not directly originated by the use of any particular article of food, nor by any climatic or telluric conditions, nor by insanitary surroundings, neither does it peculiarly affect any race or caste.
"5. Leprosy is indirectly influenced by insanitary surroundings, such as poverty, bad food, or deficient drainage or ventilation, for these by causing a predisposition increase the susceptibility of the individual to the disease.
"6. Leprosy, in the great majority of cases, originates de novo, that is, from a sequence or concurrence of causes and conditions dealt with in the Report, and which are related to each other in ways at present imperfectly known."
The practical suggestions of the Commission for preventive treatment included voluntary isolation, prohibition of the sale of articles of food by lepers, leper farms, orphanages, and "improved sanitation and good dietetic conditions" generally. Serum-therapy has been attempted on behalf of the French Academy of Medicine, but without success. Many forms of treatment ameliorate the miserable condition of the leper, but up to the present no curative agent has been found.
Diplococcus of Pneumonia
Pneumonia. Some of the difficulty which has surrounded the bacteriology of inflammation of the lungs is due to the confusion arising from supposing that attacks of the disease differed only in degree. Pneumonia, however, has various forms, arising now from one cause, now from another. The specific or croupous pneumonia is associated with two organisms: Fraenkel's diplococcus and Friedländer's pneumo-bacillus. Several other bacteria have from time to time been held responsible for pneumonia, a streptococcus receiving, at one time, some support. But whilst opinion is divided on the rôle of various extraneous and concomitant bacteria in lung disease, importance is attached to Fraenkel's and Friedländer's organisms.
The diplococcus of Fraenkel is a small, oval diplococcus found in the "rusty" sputum of croupous pneumonia. It is non-motile, non-liquefying, and aërobic. When examined from cultures the diplococci are frequently seen in chains, not unlike a streptococcus, and there is some reason to suppose that this form gave rise to the belief that it was another species; when examined from the tissues it possesses a capsule, but in culture this is lost. It is difficult to cultivate, but grows on glycerine agar and blood serum at blood-heat. On ordinary gelatine at room temperature it does not grow, or, if so, very slightly. The ideal fluid is a slightly alkaline liquid medium, and in twenty-four hours a powdery growth will occur in such broth. On potato there is apparently no growth. It rapidly loses its virulence on solid media, and is said to be non-virulent after three or four sub-culturings. A temperature of 54–58° C. for a few minutes kills the bacteria, but not the toxin. This, however, is removed by filtration, and is therefore probably intracellular. It is attenuated by heating to 70° C.
Fraenkel's diplococcus occurs, then, in the acute stage of pneumonia, in company with streptococci and staphylococci. It also occurs in the blood in certain suppurative conditions, in pleurisy and inflammation of the pericardium, and sometimes in diphtheria, and therefore it is not peculiar to pneumonia.
There is one other point to which attention should be drawn. Fraenkel's organism is said to be frequently present in the saliva of healthy persons. Pneumonia depresses the resistant vitality of the tissues, and thus affords to the diplococcus present in the saliva an excellent nidus for its growth.
Friedländer's Pneumo-bacillus is a capsulated oval coccus, assuming the form of a small bacillus. It is inconstant in pneumonia, unequally distributed, and scarce; it is aërobic, and facultatively anaërobic; it occasionally occurs in long forms and filaments; it is non-motile, non-liquefying, and has no spores; it does not stain by Gram's method, which stain is therefore used for differential diagnosis; it will grow fairly well in ordinary gelatine at 20° C.; and it is a denitrifying organism, and also an actively fermentative one, even fermenting glycerine. It is not unlike Bacillus coli communis, and to distinguish it from that organism we may remember that the B. coli is motile, never has a capsule, produces indol, and does not ferment glycerine.
Bacillus of Influenza
Influenza. In 1892, during the pandemic of influenza, Pfeiffer discovered a bacillus in the bronchial mucus of patients suffering from the disease. It is one of the smallest bacilli known, and frequently occurs in chains not unlike a streptococcus. Carron obtained the same organism from the blood. In the bronchial expectoration it can retain its virulence for as long as a fortnight, but it is quickly destroyed by drying. The bacillus is aërobic, non-motile, and up to the present spores have not been found. It grows somewhat feebly in artificial media, and readily dies out. Blood serum, glycerine agar, broth, and gelatine have all been used at blood-heat. It does not grow at room temperature. Pfeiffer's bacillus appears most abundantly at the height of the disease, and disappears with convalescence. It is said not to appear in any other disease.
Yellow Fever. Sternberg and Havelburg have both isolated bacilli from cases of yellow fever; but the organism discovered by Sanarelli, the Bacillus icteroides, is now accepted as the causal agent of the disease. It is a small, short rod, with round ends, and generally united in pairs; it has various pleomorphic forms; it grows well on all the ordinary media; it is killed in sea-water at 60° C., and also by direct sunlight in a few hours.
Diarrhœa of Infants. From time to time different organisms have been isolated in this diseased condition. Bacillus coli and B. enteriditis sporogenes (Klein) have been held responsible for it. W. D. Booker, of Johns Hopkins University, sums up an extended research into the question as follows:
"No single micro-organism is found to be the specific exciter of the summer diarrhœa of infants, but the affection is generally to be attributed to the result of the activity of a number of varieties of bacteria, some of which belong to well-known species, and are of ordinary occurrence and wide distribution, the most important being the streptococcus and Proteus vulgaris.
"The first step in the pathological process is probably an injury to the epithelium from abnormal or excessive fermentation, from toxic products of bacteria, or from other factors.
"Bacteria exert a direct injury upon the tissues in some instances, whereas in others the damage is brought about indirectly through the production of soluble poisons."
Actinomycosis. This disease affects both animals and man. As Professor Crookshank points out, it has long been known in this country,[100] but its various manifestations have been mistaken for other diseases or have received popular names.
Here we can only mention the most outstanding facts concerning the disease. It is caused by the "ray fungus," or Streptothrix actinomyces, which, growing on certain cereals, often gains entrance to the tissues of man and beast by lacerations of the mucous membrane of the mouth, by wounds, or by decayed teeth. Barley has been the cereal in question in some cases. The result of the introduction of the parasite is what is termed an "infective granuloma." This is, generally speaking, of the nature of an inflammatory tumour composed of round cells, epithelioid cells, giant cells, and fibrous tissue, forming nodules of varying sizes. In some cases they develop to large tumours, in others they soon break down. Actinomycosis in some ways closely resembles tuberculosis in its tissue characters.
In the discharge or pus from human cases of the disease small sulphur-yellow bodies may be detected, and these are tufts of "_clubs_" which are the broken-down rays of the parasite; for in the tissues which are affected the parasite arranges itself in a radiate manner, growing and extending at its outer margin and degenerating behind. In cattle the centre of the old ray becomes caseated, like cheese, or even calcified, like a stone. In the human disease abundant "_threads_" are formed as a tangled mass in the middle of the colony. As clubs characterise the bovine actinomycosis, so threads are a feature of the human form of the disease. But in both there is a third element, namely, small round cells, called by some spores, by others simply cocci. Authorities are not yet agreed as to the precise significance and rôle of these round cells. The life-history of the micro-organism may be summed up thus:
"The spores sprout into excessively fine, straight or sinuous, and sometimes distinctly spirilliform threads, which branch irregularly and sometimes dichotomously. The extremities of the branches develop the club-shaped bodies. The clubs are closely packed together, so that a more or less globular body is formed, with a central core composed of a dense mass of threads" (Crookshank).
Possibly these clubs represent organs of fructification, and produce the spores. These latter are, it is believed, set free in the vicinity of the ray, and create fresh centres of disease.
In man the disease manifests itself in various parts according to the locality of entrance. When occurring in the mouth it attacks the lower jaw most frequently. In one recorded case the disease was localised to the bronchi, and did not even extend into the lungs. It was probably contracted by inhalation of the parasite. The disease may spread to distant parts by means of the blood stream, and frequently the abscesses are apt to burrow in various directions.
In the ox the disease remains much more localised, and frequently occurs in the lower jaw, palate, or tongue. In the last site it is known as "wooden tongue," owing to the hardness resulting. The skin and subcutaneous tissues are also a favourite seat of the disease, producing the so-called wens or clyers so commonly seen in the fen country (Crookshank). Actinomycosis in cattle is specially prevalent in river valleys, marshes, and on land reclaimed from the sea. The disease occurs at all seasons, but perhaps more commonly in autumn and winter. It is more frequently met with in young animals. The disease is probably not hereditary nor readily communicated from animal to animal.
Actinomyces may be cultivated, like other parasitic diseases, outside the body. Gelatine, blood serum, agar, glycerine agar, and potato have been used for this purpose. After a few days on glycerine agar at the temperature of the blood little white shining colonies appear, which increase and coalesce. In about ten days' time the culture often turns a bright yellow, though it may remain white or even take on a brown or olive tint. The entire mass of growth is raised dry and crinkled, and composed almost exclusively of threads. In its early stage small bacillary forms occur, and in its later stage coccal forms. True clubs never occur in pure cultures, although the threads may occasionally show bulbous endings.
Glanders in the horse and ass, and sometimes by communication in man also, is caused by a short, non-motile, aërobic bacillus, named, after the old Roman nomenclature (malleus), Bacillus mallei. It was discovered in 1882 by Löffler and Schütz. It is found in the nasal discharge of glandered animals. In appearance the bacillus is not unlike B. tuberculosis, except that it is shorter and thicker. The beading of the bacillus of glanders, like that in tubercle, does not denote spores. B. mallei can be cultivated on the usual media, especially on glycerine agar and potato. On the latter medium it forms a very characteristic honey-like growth, which later becomes reddish-brown.
In the horse glanders particularly affects the nasal mucous membrane, forming nodules which degenerate and emit an offensive discharge. From the nose, or nasal septum, as a centre, the disease spreads to surrounding parts. It may also occur as nodules in and under the skin, when it is known as "farcy." Persons attending a glandered animal may contract the disease, often by direct inoculation.
Mallein is a substance analogous to tuberculin, and is made by growing a pure culture of Bacillus mallei in glycerine-veal broth in flat flasks, with free access of calcined air. After a month's growth the culture is sterilised, filtered, concentrated, and mixed with an equal volume of a .5 per cent. solution of carbolic. The dose is 1 cc., and it is used, like tuberculin, for diagnostic purposes. If the suspected animal reacts to the injection, it is suffering from glanders. Reaction is judged by three signs, namely, a rise of temperature 2–3° C., a large "soup-plate" swelling at the site of inoculation, and an enlargement of the lymphatic glands.
Swine fever, foot-and-mouth disease, chicken cholera, dysentery, rinderpest, and other diseases of animals have micro-organisms intimately related to them.
There is a group of diseases due to the presence in the blood or tissues of hæmatozoa, that is, protozoa which can live and perform their function in the blood. Amongst these are malaria, sleeping sickness, and other tropical diseases in man, and surra and various hæmatozoa in horses, fish, frogs, or rats.
Malaria. Although a Bacillus malariæ has been described as the cause of this disease, it is now almost universally supposed that the true cause is a protozoan parasite. In 1880 Laveran first described this organism, and the discovery was confirmed by Marchiafava, Celli, and others. Laveran claimed that it occurred in four different forms during the progress of its life-history:
(a) Spherical or Irregular Bodies attached to the blood corpuscle, or free in the blood plasma. They are a little smaller than the blood-cells, and may or may not contain pigment. They eventually invade the corpuscles, possess more pigment, and lose their amœboid movement. Within the red blood corpuscles they increase in size until they reach the adult stage.
(b) Segmentation Forms, often assuming a rosette shape, follow next. They are pigmented, are possibly a sporing stage, and are finally set free in the blood.
(c) The Crescents, or Semilunar Bodies, are free in the blood, but motionless. They are colourless, have a distinct membrane, and generally show a little pigment about the middle; they taper towards the poles. They appear in the blood after the fever has existed for some time, occurring chiefly, sometimes only, in the quotidian and malignant types of malaria.
(d) The Flagellated Bodies apparently occur only in the blood outside the body. They are extracorpuscular bodies, and possess several long flagella, and are therefore actively motile. They are derived from the crescents or irregular intracorpuscular bodies.
What is the precise significance of these various forms and modifications of them is not at present known. Possibly the semilune is a resting stage inside the body, and the flagellated body another similar stage outside. Attempts to cultivate the parasite outside the body have failed. There is a good deal of evidence to show that the mosquito is the host outside the human body. There may be different forms and varieties of parasite, if not actually different species, causing the diverse forms of clinical malaria.
The above account of diseases caused by bacteria does not profess to be in any sense exhaustive. It is merely illustrative. It reveals some of the disease-producing powers of micro-organisms. There are a large number of other diseases in which bacteria have been found. They are not the causes, but only accidentally present or associated with "secondary infection." Variola (small-pox), scarlet fever, and measles are excellent examples. It is possible that the danger at the present time is rather in the direction of supposing that every disease will readily yield its secret to the bacteriologist. Such, of course, is not the case. Nevertheless, as in the past, so in the future, constant research and patient investigation is the only hope we have for the elucidation of truth in respect to the causes of disease.
CHAPTER IX
DISINFECTION
The object of modern bacteriology is not merely to accumulate tested facts of knowledge, nor only to learn the truth respecting the biology and life-history of bacteria. These are most important things from a scientific point of view. But they are also a means to an end; that end is the prevention of preventable diseases and the treatment of any departure from health. In a science not a quarter of a century old much has already been accomplished in this direction. The knowledge acquired of, and the secrets learned from, these tiny vegetable cells which have such potentiality for good or evil have been, in some degree, turned against them. When we know what favours their growth and vitality and virulence, we know something of the physical conditions which are inimical to their life; when we know how to grow them, we also know how to kill them.
We have previously made a cursory examination of the methods which are adopted for opposing bacteria and their products in the tissues and body fluids. We must now turn to consider shortly the modes which may be adopted in preventive medicine for opposing bacteria outside the body.
It will be clear at once that we may have varying degrees of opposition to bacteria. Some substances kill bacteria, and they are known as germicides; other substances prevent their development and resulting septic action, and these are termed antiseptics. The word disinfectant is used more or less indiscriminately to cover both these terms. A deodorant is, of course, a substance removing the odour of evil-smelling putrefactive processes. Here, then, we have the common designations of substances able to act injuriously on bacteria and their products outside, or upon the surface of, the body. But a moment's reflection will bring to our minds two facts not to be forgotten. In the first place, an antiseptic applied in very strong dose, or for an extended period, may act as a germicide; and, vice versâ, a germicide in too weak solution to act as such may perform only the function of an antiseptic. Moreover, the action of these disinfecting substances not only varies according to their own strength and mode of application, but it varies also according to the specific resistance of the protoplasm of the bacteria in question. Examples of the latter are abundant, and readers who have only assimilated the simple facts set forth in these pages are aware that between the bacillus of diphtheria and the spores of anthrax there is an enormous difference in power of resistance. In the second place, reflection will enable us to recall what has already been said, when discussing the requirements necessary for bacterial growth, respecting the physical conditions injurious to development. In a cold temperature, as a general rule, bacteria do not multiply with the same rapidity as at blood-heat. Within the limits of a moist perimeter the air is, to all intents and purposes, germ-free. Direct sunlight has a definitely germicidal effect in the course of time upon some of the most virulent bacteria we know. Here, then, are three examples of physical agents—low temperature, moist perimeter, sunlight—which, if strong enough in degree, or acting for a long enough period of time, become first antiseptics and then germicides. Yet for a limited period they have no injurious effect upon bacteria. These are simple points, and call for little comment, yet the pages of medical and sanitary journals reveal not a few keen controversies upon the injurious action of certain substances upon certain bacteria owing to the discrepancies, of necessity arising, between results of different skilled observers who have been carrying out different experiments with different solutions of the same substance upon different protoplasms of the same species of bacteria. We feel no doubt that in these pioneering researches much labour has been to some extent misspent, owing to the neglect of a common denominator. Only a more accurate knowledge of bacteria or a recognised standard for disinfecting experiments can ever supply such common denominator.
Species of bacteria for comparative observation-experiments upon the action of chemical or physical agents must be not only the same species, but cultured under the same conditions, and treated by the agent in the same manner, otherwise the results cannot be compared upon a common platform, or with any hope of arriving at exactly the same conclusions.
Sir George Buchanan laid down, in 1884, a very simple and suitable standard of what true disinfection meant, viz., the destruction of the most stable known infective matter. Such a test is high and difficult to attain unto; nevertheless, it is the only satisfactory one. Obviously many substances which are useful antiseptics in practical life would fall far short of such a standard, yet for true and complete disinfection such an ideal is the only adequate one.
Quite recently three or four workers at Leipzig[101] have drawn up simple directions, the adoption of which would considerably assist in securing a common standard for disinfectant research. They are as follows:
1. In all comparative observations it is imperative that molecularly equivalent quantities of the reagents should be employed.
2. The bacteria serving as test objects should have equal power of resistance.
3. The numbers of bacteria used in comparative observation should be approximately equal.
4. The disinfecting solution must be always used at the same temperature in comparative experiments.
5. The bacteria must be brought into contact with the disinfectant with as little as possible of the nutrient material carried over. (This obviously will depend upon the object of the research.)
6. After having been exposed to the disinfectant for a fixed time, they should be freed from it as far as possible.
7. They should then be returned in equal numbers to the respective culture medium most favourable to the development of each, and kept at the same, preferably the optimum, temperature for their growth.
8. The number of surviving bacteria capable of giving rise to colonies in solid media must be estimated after the lapse of equal periods of time.
We may now turn from general principles to mention shortly some of the commoner methods and substances adopted to secure efficient disinfection. They are all divisible, according to Sir George Buchanan's standard, into two groups:
1. Heat in various forms;
2. Chemical bodies in various forms.
It should at the outset be understood that we desire in practical disinfection to inhibit or kill micro-organisms without injury to, or destruction of, the substance harbouring the germs for the time being. If this latter is of no moment, as in rags or carcasses, burning is the simplest and most thorough treatment. But with mattresses and beddings, bedclothes and garments, as well as with the human body, it is obvious that something short of burning is required.
1. From the earliest days of bacteriology heat has held a prominent place as a disinfector. But it is only in comparatively recent times that it has been fully established that moist heat is the only really efficient form of heat disinfection. Boiling at atmospheric pressure (100° C.) is the oldest form of moist heat disinfection, and because of the simplicity of its application it has gained a large degree of popularity. But it must not be forgotten that mere boiling (100° C.) may not effectually remove the spores of all bacilli. Besides, boiling is not applicable to furniture, mattresses, and such-like frequently infected objects. For many of these hot-air ovens were used in the early days. But it was found that such disinfection was no disinfection at all, for not only did it leave many organisms and spores untouched, but the degree of temperature was rarely, if ever, uniform throughout the substance being treated.
The failures following in the track of these methods were an indication of the need of some form of moist heat, viz., steam.
Here it will be necessary to digress for a moment into some of the characters of steam. When water is heated certain molecular changes take place, and at a certain temperature (100° C., 212° F.) the water becomes steam, or vapour, and on very little cooling will condense. But if the vapour is heated, it will become practically a gas, and will not condense until it has lost the whole of the heat, i. e., the heat of making water into vapour plus the heat of making vapour into gas. A gas proper is, then, the vapour of a liquid of which the boiling-point is substantially below its actual temperature. But we know that the temperature at which it boils depends upon the pressure to which it is subjected (Regnault's law). Hence in reality "steam at any temperature whatever may be a vapour proper, provided the pressure is such as prevents the liquid from boiling below that temperature." In such a condition of vapour it is termed saturated steam. But if it is at that same pressure further heated, it becomes practically a gas, and is called superheated steam. The former can condense without cooling; the latter cannot so condense at the same pressure. Saturated steam condenses immediately it meets the object to be disinfected, and gives out its latent heat; superheated steam acts by conduction, and not uniformly throughout the object. Its advantage is that it dries moistened objects. As a disinfecting power, superheated steam is much less than saturated steam. There is one further term which must be defined, namely, current steam. This is steam escaping from a disinfector as fast as it is admitted, and may be at atmospheric or higher temperatures. The disinfecting temperature which is now used as a standard is an exposure to saturated steam of 115° C. for fifteen minutes.
A number of different kinds of apparatus have been invented to facilitate disinfection to this standard on a large scale. Most sanitary authorities of importance are now supplied with some form of steam disinfector, though many are unable to go to the expense of high-pressure disinfectors. Professor Delépine has pointed out[102] that a current of steam at low pressure may completely disinfect. Whilst such simple current-steam machines have thus been demonstrated as efficient bactericides, for all practical purposes it is important to have disinfectors capable of giving temperatures considerably above 100° C., of simple construction, having steam power of uniform temperature and rapid penetration, and containing, when in action, a minimum of superheated steam. In addition to these characters of a first-rate steam disinfector, two other important points should be borne in mind, namely, the air must be completely ejected from the disinfection chamber before the results due to steam are obtained, and some sort of automatic index giving a record of each disinfection is indispensable.
We may turn from these general principles to mention shortly some of the types of steam disinfectors most commonly in use. They are four, namely, the Washington Lyon, the Equifex (Defries), the Thresh, and the Reck.
Washington Lyon's apparatus consists of an elongated boiler having double walls, with a door at each end. The body of the apparatus is jacketed. The whole is large enough to admit of bedding and mattresses, and generally is so arranged that one end opens into one room, and the other end opens into another room. This convenient position admits of inserting infected articles from one room and receiving them disinfected into the other room. Possible reinfection is thereby prevented. Steam is admitted into the jacket at a pressure of between twenty and twenty-five pounds, and is generally twenty pounds in the interior of the cylinder. At the end of the operation a partial vacuum is created, by which means much of the moisture on the articles may be removed. In some cases a current of warm air is admitted before disinfection in order to diminish the extent of condensation.
The Equifex (Defries) contains no steam jacket, but coils of pipes are placed at the top and bottom of the apparatus, with the object of imparting to the steam as much heat as is lost by radiation through the walls of the disinfecting chamber, and at the same time of preventing undue condensation. The air is first removed by a preliminary current of steam, after which steam at a pressure of ten pounds is intermittently introduced and allowed to escape. The object of this proceeding is to remove air from the pores of the articles to be disinfected by the sudden expansion of the film of water previously condensed on their surface. The apparatus introduced by Dr. Thresh was constructed with a view of overcoming the objection to some of the other machines that bulky articles retained a large percentage of moisture, thus necessitating the use of some additional drying apparatus. A central chamber receives the articles to be disinfected, and is surrounded by a boiler containing a solution of calcium chloride at a temperature of 225° F. This is heated by a small furnace, and the steam given off (218–300° F.) is conducted into the central chamber. The steam is not confined under any pressure except that of the atmosphere. When the steam has passed for a sufficient length of time, it is readily diverted into the open air. Hot air is now introduced, and at the expiration of an hour the articles may be taken out disinfected and as dry as they were when inserted. The apparatus is comparatively inexpensive, and not of a complicated nature. The current steam is saturated, and at a temperature a few degrees above the boiling-point. Many experiments have been performed with this apparatus, and there is now a large amount of evidence in favour of it and current steam disinfection.
Reck's apparatus is another kind of saturated steam disinfector, which resembles the Equifex, but differs from it in employing steam as a current.
It is probable that many other forms of steam disinfector will be invented, and each will have its enthusiastic supporters. Even at the time of writing some excellent results are announced from America.
2. The effects of chemical substances as solutions, or in spray form, upon bacteria have been observed from the earliest days of bacteriology. To some decomposing matter or solution a disinfectant was added and sub-cultures made. If bacteria continued to develop, the disinfection had not been efficient; if, on the other hand, the sub-culture remained sterile, disinfection had been complete. From such rough-and-ready methods large deductions were drawn, and it is hardly too much to say that no branch of bacteriology contains such a vast mass of unassimilated and unassimilable statements as that relating to research into disinfectants. Most of the tabulated and recorded results are conspicuous in having no standard as regards bacterial growth. Yet without such a standard results are not comparable.
Silk threads, impregnated with anthrax spores, were placed in bottles containing carbolic acid of various strengths, and at stated periods threads were removed and placed in nutrient media, and development or otherwise observed. But, as Professor Crookshank[103] has pointed out, this method is fallacious, the thread being still wet with the solution when transferred to the medium, and thus modified in culture, possibly even inhibited altogether. It is unnecessary for us here to discuss every mode adopted by investigators in similar researches. We may just mention that the most approved methods at the present time are based upon two simple plans of exposure. In one we use a known volume of recent broth culture of an organism grown under specified conditions. To this is added a measured quantity of the antiseptic. At stated periods loopfuls of the broth and antiseptic mixture are sub-cultured in fresh-sterilised broth, and resulting development or otherwise closely observed. The other method is practicable when we are dealing with volatile bodies. In such cases a standard culture is made of the organism in broth at a standard temperature. Into this are dipped small strips of sterilised linen. When thoroughly impregnated these are removed from the broth and subsequently dried over sulphuric acid in a vacuum at 38° C. These may now be exposed for a longer or shorter period to the fumes of the antiseptic in question, and broth cultures made at the end of the exposure. It is obvious that a very large number of modifications are possible of these two simple devices for testing the bactericidal power of chemical substances. It should be remembered that here, perhaps, more than anywhere else in bacteriological research, careful control experiments are absolutely necessary.
Mineral acids (nitric, hydrochloric, sulphuric), especially concentrated, are all germicides.
The halogens—chlorine, bromine, iodine, and fluorine—are, all four, disinfectants, but not used in practice. They are named in their order of power as such.
A number of separate bodies, such as chloroform and iodoform, have been much advocated as antiseptics. The cost of the former and odour of the latter have, however, greatly militated against their general adoption.
Chloride of lime is a powerful disinfectant. Professor Sheridan Delépine and Dr. Arthur Ransome have demonstrated its germicidal effect as a solution applied directly to the walls of rooms inhabited by tuberculous patients.[104] It may also be used in solid form for dusting decomposing matter.
Mercuric chloride (corrosive sublimate) has been an accepted germicide for some time. But the experiments of Behring, Crookshank, and others have proved that the weaker solutions cannot be relied upon. This is, in part, due to the fact that it forms in albuminous liquids an albuminate of mercury which is inactive. Dilute solutions have the further disadvantage of being unstable. Various authorities recommend a solution of 1–500 as a germicide, and much weaker solutions are, of course, antiseptic. An ounce each of corrosive sublimate and hydrochloric acid in three gallons of water makes an efficient disinfectant.
Potassium permanganate is, of course, the chief substance in Condy's fluid, as zinc chloride is in Burnett's disinfecting fluid. A 5 per cent. of the former and a 2-1/2 per cent. of the latter are germicidal.
Boracic acid is one of the most useful antiseptics with which to wash sore eyes, or preserve tinned foods or milk. It is not a strong germicide, but an unirritating and effective wash. Many cases of its addition to milk have found their way into the law courts, owing to cumulative poisoning, and it should only be used with the very greatest care as a food preservative.
Carbolic acid has come into prominence as an antiseptic since its adoption by Lister in antiseptic surgery. It is cheap, volatile, and effective. One part in 400 is antiseptic, and 1 in 20 germicidal. As a wash for the hands the former is used, and a weaker solution for the body generally. Carbolic soap and similar toilet combinations are now very common. At one time it appeared as if corrosive sublimate would oust carbolic from the first place as an antiseptic solution, but a large number of experiments have confirmed opinion in favour of carbolic. Professor Crookshank found that carbolic acid, 1 in 40, acting for only one minute is sufficient to destroy Streptococcus pyogenes, S. erysipelatis, and Staphylococcus pyogenes aureus, and in the strength of 1 in 20 carbolic acid completely sterilised tubercular sputum when shaken up with it for one minute.
Creosol, a member of the phenol series, is a good disinfectant, and the active element in lysol, Jeye's fluid, creoline, izal, and creosote.
Sulphurous acid is one of the commonest disinfectants employed for fumigation—the old orthodox method of disinfecting a room in which a case of infective disease has been nursed. It is evolved, of course, by burning sulphur. For each thousand cubic feet from one to five pounds of sulphur is used, and the walls may be washed with carbolic acid. Dr. Kenwood carried out some experiments in 1896[105] which appear to support the disinfecting power of sulphur fumes. He found that the Bacillus diphtheriæ was not killed, though markedly inhibited, when the sulphurous gas (SO2) did not much exceed .25 per cent. But the bacillus was killed where the sulphur fumes exceeded .5 per cent. Both these results had reference to the
SO2 in the air in the centre of the room at a height of four feet, and after the lapse of four hours. There can be little doubt that fuming a sealed-up room with sulphur fumes in a moist atmosphere, and leaving it thus for twenty-four hours, is generally, if not always, efficient disinfection. It will kill the bacillus of diphtheria, though not always more resistant germs. Moreover, its simplicity of adoption is greatly in its favour. Anyone can readily apply it by purchasing a few pounds weight of ordinary roll sulphur and burning this in a saucer in the middle of a room which has had all its crevices and cracks in windows and walls blocked up with pasted paper. Nitrous fumes may also be used in this way.
Recently formalin has come much in favour as a room disinfectant. Formalin is a 40 per cent. solution of formaldehyde in water, a gas discovered by Hofmann in 1869. This gas is a product of imperfect oxidation of methyl alcohol, and may be obtained by passing vapour of methyl alcohol, mixed with air, over a glowing platinum wire or other heated metals, such as copper and silver. It is the simplest of a series of aldehydes, the highest of which is palmitic aldehyde. Its formula is CH2O, and it is a colourless gas with a pungent odour, and having penetrating and irritating properties, particularly affecting the nasal mucous membrane and the eyes of those working with it. It is readily soluble in water, and in the air oxidises into formic acid (CH2O2). This latter substance occurs in the stings of bees, wasps, nettles, and various poisonous animal secretions. Formalin is a strong bactericide even in dilute solutions, and, of course, volatile. A solution of 1 to 10,000 is said to be able to destroy the bacilli of typhoid, cholera, and anthrax. A teaspoonful to ten gallons of milk is said to retard souring. When formalin is evaporated down, a white residue is left known as paraform. In lozenge form this latter body is used by combustion of methylated spirit to produce the gas. Hence we have three common forms of the same thing—formalin, formic aldehyde, paraform—each of which yields formic acid, and thus disinfects. The vapour cannot in practice be generated from the formalin as readily as from the paraform.
By a variety of ingenious arrangements formic aldehyde has been tested by a large number of observers during the last two or three years. We may refer to three modes of application. 1. The sprayer (Equifex apparatus) produces a mixture of air and solution for spraying walls, ceilings, floors, and sometimes garments. 2. The autoclave (Trillat's apparatus). In this a mixture of a 30–40 per cent. watery solution of formaldehyde and calcium chloride (4–5 per cent.) is heated under a pressure of three or four atmospheres, and the almost pure, dry gas is conducted through a tube passing through the keyhole of the door into the sealed-up room. 3. The paraform lamp (the Alformant). The principle of this lamp is that the hot, moist products from the combustion of methylated spirit act upon the paraform tablets, converting them into gas. Most of the conclusions derived from experiments with these three different forms of apparatus are the same. It is agreed that the gas is harmless to colours and metal and polished wood. The vapour acts best in a warm atmosphere. As for its action on bacteria, it compares favourably with any other disinfectant. In 1 per cent. solution formalin destroys non-spore-bearing bacteria in thirty to sixty minutes.
Many observers have decried formaldehyde on account of its professed lack of penetrating power. Professor Delépine, however, states[106] that it possesses "penetration powers probably greater than those of most other active gaseous disinfectants. Bacillus coli, B. tuberculosis, B. pyocyaneus, and Staph. pyogenes aureus were killed in dry or moist state, even when protected by three layers of filter paper." In
Professor Delépine's opinion, the vapours of phenol, izal, dry chlorine, and sulphurous acid have, under the same conditions, given inferior results.
We may now shortly summarise the foregoing facts respecting antiseptics and disinfection in the simplest terms possible to afford facility to the uninitiated in practical application:
To disinfect a room, seal up cracks and crevices, and burn at least one pound of roll sulphur for every 1,000 cubic feet of space.[107] Many authorities recommend four or five pounds of sulphur to the same space. Let the room remain sealed up for twenty-four hours.
To disinfect walls, wash with chloride of lime solution (1–100) or carbolic acid (1–40). This latter solution may be used to wipe down furniture. Either or both may be used after sulphur fuming. Formic aldehyde may also be used by lamp or autoclave.
To disinfect bedding, etc., the steam sterilisation secured in a Thresh, Equifex, or Lyon apparatus is the best. Rags and infected clothing, unless valuable, should be burnt.
To disinfect garments and wearing apparel, they should be washed in a disinfectant solution, or fumed with formic aldehyde.
To disinfect excreta or putrefying solutions, enough disinfectant should be added to produce in the solution or matter being disinfected the percentage of disinfectant necessary to act as such. Adding a small quantity of antiseptic to a large volume of fluid or solid is as useless as pouring a small quantity of antiseptic down a sewer with the idea that such treatment will disinfect the sewage. The mixture of the disinfectant with the matter to be disinfected must contain the standard percentage for disinfection. Chloride of lime is a common substance for use in this way. Potassium permanganate (1–100) and carbolic (1–100), and many manufactured bodies containing them, are also widely used. Drs. Hill and Abram recommend[108] that the excreta and disinfectant be thoroughly mixed and stand for at least half an hour. For various reasons they particularly advise chinosol as the most convenient disinfectant for this specific purpose.
Antiseptics for wounds. Carbolic acid (1–40) or corrosive sublimate (1–1,000) are commonly used in surgical practice. Boracic acid is one of the most unirritating antiseptics which are known. It may be used in saturated watery solution (1–30) or dusted on copiously as fine powder. It is especially applicable in open wounds, and as an eye-wash.
To disinfect hands and arms. Operating surgeons are those to whom it is a most urgent necessity to cleanse hands and arms antiseptically. Carbolic acid (1–20, or 1–40) is used for this purpose.
It is hardly necessary to add that in a case of infectious disease occurring in a household many of these modes of application, perhaps all of them, must be adopted. Formalin is probably the best gaseous disinfectant which we have, but its use does not, and should not, preclude the simultaneous adoption of other methods.
[APPENDIX]
It is proposed to add one or two notes on certain technical points in bacteriological work, with a view to assisting those medical men not able to obtain the advantages of a well-equipped laboratory, and yet desirous of occasionally attempting some practical bacteriology.
1. General Examination. All fluids may be examined for bacteria in two chief ways:
(a) A small quantity may be placed on a cover-glass or slide, dried over a lamp or bunsen flame, and stained with aniline dyes for a few minutes. It is then ready for microscopic examination. It is obvious that the result will generally be a mixture of bacteria, for which differentiating stains may be used (Gram, Ziehl-Neelsen, etc.).
(b) A minute drop of the suspected fluid may be added to various fluid media (broth, liquefied gelatine, etc.) and then plated out upon small sterilised sheets of glass. In the course of two or three days the contained bacteria will reveal themselves in characteristic colonies, which may be examined, and if possible sub-cultured, and carefully studied.
Double-Staining Methods. These are various, and are used when it is desired to stain the bacteria themselves one colour, and the matrix or ground substance in which they are situated another colour. Three of the commoner methods are those of Ehrlich, Neelsen, and Gram. They are as follows:
Ehrlich's Method. "Five parts of aniline oil are shaken up with 100 parts distilled water, and the emulsion filtered through moistened filter paper. A saturated alcoholic solution of fuchsine, methyl-violet, or gentian-violet is added to the filtrate in a watch-glass, drop by drop, until precipitation commences. Cover-glass preparations are floated in this mixture for fifteen to thirty minutes, then washed for a few seconds in dilute nitric acid (one part nitric acid to two of water), and then rinsed in distilled water. The stain is removed from everything except the bacilli; but the ground substance can be after-stained brown if the bacilli are violet, or blue if they have been stained red" (Crookshank, Bacteriology and Infective Diseases, p. 89).
Gram's Method. The primary stain in this method is a solution of aniline gentian-violet (saturated alcoholic solution of gentian-violet 30 cc., aniline water 100 cc.), which stains both ground substance and bacteria in purple. The preparation is next immersed in the following solution for half a minute or a little more:
| Iodine | 1 part |
| Potassium iodide | 2 parts |
| Distilled water | 300 parts |
In this short space of time the iodine solution acts as a mordant of the purple colour in the bacteria, but not in the ground substance. Hence, if the preparation be now (when it has assumed a brown colour) washed in alcohol (methylated spirit), the ground substance slowly loses its colour and becomes clear. But the bacteria retain their colour, and thus stand out in a well-defined manner. Cover-glass preparations decolourise more quickly than sections of hardened tissue, and they should only be left in the methylated spirit until no more colour comes away. The preparation may now be washed in water, dried, and mounted for microscopic examination, or it may be double-stained, that is, immersed in some contrast colour which will lightly stain the ground substance. Eosin or Bismarck brown are commonly used for this purpose. The former is applied for a minute or two, the latter for five minutes, after which the specimen is passed through methylated spirit (and preferably xylol also) and mounted. The result is that the bacteria appear in a dark purple colour on a background of faint pink or brown. Carbol-thionine blue, picro-carmine, and other stains are occasionally used in place of the aniline gentian-violet, and there are other slight modifications of the method.
Ziehl-Neelsen Method. Here the primary stain is a solution of carbol-fuchsin:
| Fuchsin | 1 part |
| Absolute alcohol | 10 parts |
| 5 per cent. aqueous solution of carbolic acid | 100 parts |
It is best to heat the dye in a sand-bath, in order to distribute the heat evenly. The various stages in the staining process are as follows: (a) The cover-glass with the dried film upon it is immersed in the hot stain for one to three minutes. (b) Remove the cover-glass from the carbol-fuchsin, and place it in a capsule containing a 25 per cent. solution of sulphuric acid to decolourise it. Here its redness is changed into a slate-grey colour. (c) Wash in water, and alternately in the acid and water, until it is of a faint pink colour. (d) Now place the cover-glass for a minute or two in a saturated aqueous solution of methylene-blue, which will counter-stain the decolourised ground substance blue. (e) Wash in water. (f) Dehydrate by rinsing in methylated spirit, dry, and mount. A pure culture of bacteria will not necessarily require the counter-stain (methylene-blue). Sections of tissue may require twenty to thirty minutes in the primary stain (carbol-fuchsin). This stain is used for tubercle and leprosy. With a little practice the staining of the bacillus of tubercle when present in pus or sputum becomes a very simple and accurate method of diagnosis. A small particle of sputum or pus is placed between two clean cover-glasses and thus pressed between the thumb and finger into a thin film. This is readily dried and stained as above, the bacillus of tubercle appearing as a delicately-beaded red rod with a background of blue.
Bacteriological Diagnosis. The following points must be ascertained in order to identify any particular micro-organism:
(1) Its morphology, bacillus, coccus, spirillum, etc.; the presence or absence of involution forms.
(2) Motility by the unstained cover-glass preparation ("hanging drop"); note presence of flagella.
(3) Presence of spores, their appearance and position.
(4) Whether or not the organism stains with Gram's method.
(5) The character of the growth upon various media (gelatine, agar, milk, potato, broth); the presence or absence of liquefaction in the gelatine culture; its power of producing acid, gas, or indol.
(6) Whether it is aërobic or anaërobic.
(7) Its colour in cultivation.
(8) If it is a disease-producing organism under examination, its effect upon the animal tissues and the course of the disease should be observed.
There are other points of importance, but the above are essential to a right conclusion.
Diagnosis in Special Diseases:
(1) Diphtheria. This disease may be bacteriologically diagnosed with a minimum of apparatus and equipment. By means of a swab a rubbing from a suspected throat is readily obtained. This may be examined by the microscope, or sub-cultured on favourable medium. Blood serum is perhaps the best, but, as Hewlett remarks, "If no serum tubes can be had, an egg may be used. It is boiled hard, the shell chipped away from one end with a knife sterilised by heating, and the inoculation made on the exposed white surface; the egg is then placed, inoculated end down, in a wine-glass of such a size that it rests on the rim and does not touch the bottom. A few drops of water may with advantage be put at the bottom of the glass to keep the egg-white moist. The preparation is kept in a warm place for twenty-four to forty-eight hours and then examined." The examination, of course, consists in staining and preparing for the microscope and observing the form, arrangement, and characters of the organism or organisms present. A small piece of the membrane may be detached, washed in water, and stained for the bacilli.
(2) Tubercle (Ziehl-Neelsen's stain, vide supra).
(3) Typhoid (Enteric Fever).
Widal's Reaction. This diagnostic test depends upon the effect which the blood of a person suffering from typhoid fever has upon the Bacillus typhosus. The effect is twofold. In the first place, the actively motile B. typhosus becomes immotile; and secondly, there is an agglutination, or grouping together in colonies, of the B. typhosus. Neither of these features occurs if healthy human blood is brought into contact with a culture of the typhoid bacillus. There are various ways in which this "serum diagnosis" can be carried out. The simplest and quickest method is as follows: To ten drops of a twenty-four or forty-eight-hours-old neutral broth culture of the typhoid bacillus one drop of the blood serum to be tested is added. The serum and culture are rapidly mixed in the trough of a hollow ground slide (such as is used for the "hanging drop"), and a single drop is taken, placed upon an ordinary clean slide, and a cover-glass superimposed. The positive reaction of agglutination and immotility, if the blood comes from a case of typhoid fever, will probably appear within fifteen or twenty minutes. The fluid culture of typhoid may be taken from an agar culture as well as from broth. In both cases it may be desirable to filter through ordinary filter paper to remove any normally agglutinated masses of bacilli before commencing the test.
In his first experiments Widal used a test-tube in the following manner: The blood to be tested is diluted by one part of it being added to fifteen parts of broth in a test-tube. The mixture is inoculated with a drop of a typical Bacillus typhosus culture. The tube is then incubated at 37° C. for twenty-four hours, after which it is examined. If the reaction be positive, the broth appears comparatively clear, but at the bottom of the test-tube a more or less abundant sediment will be found. This is due to the clumps of bacilli having fallen owing to gravity. If, on the other hand, the reaction is negative, the broth will appear more or less uniformly turbid.
For the apparatus required to carry out the simpler methods of bacteriological work reference should be made to the standard laboratory text-books, which furnish all necessary details. A good microscope, with a 1/12 oil immersion lens, is, of course, essential. This can now be obtained for about £16 (Beck, Swift, Baker, Watson, etc.), and the other necessary apparatus is readily obtainable of Baird and Tatlock, Hatton Garden, E. C., and other makers.