Pathogenic Fungi and Moulds.
It is scarcely necessary to go back to the history of the parasitic fungi to which diseases of various kinds were early attributable. The rude microscopes of two and a half centuries ago revealed the simple fact that all decomposable substances swarmed with countless multitudes of organisms, invisible to ordinary vision. Leuwenhoek, the father of microscopy, and whose researches were generally known and accepted in 1675, tells of his discovery of extremely minute organisms in rain-water, in vegetable infusions, in saliva, and in scrapings from the teeth; further, he differentiated these living organisms by their size and form, and illustrated them by means of woodcuts; and there can be no doubt that his figures are intended to represent leptothrix filaments, vibrios, and spirilla. In other of his writings attempts are made to give an idea of the size of these “animalcules”; he described them as a thousand times smaller than a grain of sand. From his investigations a belief sprung up that malaria was produced by “animalcules,” and that the plague which visited Toulon and Marseilles in 1721 arose from a similar cause. Somewhat later on the natural history of micro-organisms was more diligently studied, and with increasing interest. Müller, in 1786, pointed out that they had been too much given to occupy themselves in finding new organisms, he therefore devoted himself to the study of their forms and biological characters, and it was on such data he based a classification. Thus the scientific knowledge gained of these minute bodies was considerably advanced, and the subject now entered upon a new phase: the origin of micro-organisms. It further resolved itself into two rival theories—spontaneous generation, and development from pre-existing germs—the discussion over which lasted more than a century. Indeed, it only ended in 1871, when the originator of the Abiogenesis theory withdrew from the contest, and the more scientific investigations of Pasteur (1861) found general acceptance. This indefatigable worker had been investigating fermentation, and studying the so-called diseases of wines and a contagious disease which was committing ravages among silkworms. Pasteur in time was able to confirm the belief that the “muscadine disease” of silkworms was due to the presence of micro-organisms, discernible only by the microscope. The oval, shining bodies in the moth, worm, and eggs had been previously observed and described by Nägeli and others, but it was reserved for Pasteur to show that when a silkworm whose body contained these organisms was pounded up in a mortar with water, and painted over the leaves of the tree upon which healthy worms were fed, all took the disease and died.
PLATE IX.
AFTER DR CROOKSHANK J. T. Balcomb. del.
TYPICAL FORMS OF BACTERIA, SCHIZOMYCETES, OR FISSION-FUNGI.
As the contagious particles were transmitted to the eggs, the method adopted for preventing the spread of the disease was as follows:—Each female moth was kept separate from the others, and allowed to deposit her eggs, and after death her body was crushed up in a mortar as before, and a drop of the fluid examined under the microscope. When any trace of muscadine was found present, the whole of the eggs and body were burnt. In this way the disease was combated, and ultimately stamped out.
Pasteur also pointed out that one form or cause of disease must not be confounded with another. For example, muscadine, a true fungus (Botrytis bassiana), should not be confounded with another disease known to attack silkworms, termed pebrin, this being caused by a bacterium, and, according to the more recent researches of Balbiani, by a Psorospermia. Botrytis is a true mould, belonging to the Oomycetes, and allied to the potato fungus, Peronospora. It is propagated by spores, which, falling on a silkworm, germinate and penetrate its body. A mycelium is then developed, which spreads throughout the body. Hyphæ appear through the skin, and bear white chalky-looking spores; these become detached, and float in the air as an impalpable dust-like smoke. Damp further develops the fungus.
Insects suffer much from the ravages of fungi. The house-fly sticking to the window-pane is seen to be surrounded by the mycelia of Penicillium racemosum (Sporendonema muscæ, or Saprolegnia feræ). In other cases Cordiceps attacks certain caterpillars belonging to the genera Cossus and Hepialus when they are buried in the sand and before their metamorphosis into chrysalides; they are killed by the rapid development of hyphæ and mycelium in their tissues.
Sphæria miletaris, a parasite of Bombyx pilyocarpa, the caterpillar of which is found on pine-trees, is one of the few fungi which may be regarded as beneficial to man, since it aids in the destruction of multitudes of these caterpillars, which otherwise would devour the young shoots and pine needles. Giard specialises other parasites of insects, which he terms Entomophoreæ. Others, E. rimosa, attack grasshoppers and the diptera, enveloping them in a dense coating of mycelium and spores, which speedily kills the victim.
The study, then, of the life-history of germs, microbes, micro-organisms, or bacteria (as they are indifferently termed), opened up a new science, that of Bacteriology. By the more recent advances in this science we are enabled to understand the very important part these minute organisms fill in the great scheme of Nature, for almost exclusively by their agency the soil is supplied with the requisite nutritive material for plant life. And, as already pointed out, wherever organic matter is present—that is, the dead and useless substances which are the refuse of life—such material is promptly seized upon by micro-organisms, by means of which histolysis is rapidly accomplished.
Bacteria require a power of from 600 to 1,000 diameters or more for the determination of the species to which they belong. The number of species has been so much increased of late that a bulky volume is found to be insufficient for their enumeration. I am, however, by the courtesy of Professor Crookshank, enabled to present my readers with the typical forms of thirty-nine species of Bacteria, Schizomycetes, or fission-fungi, a selection, it will be seen, chiefly taken from among pathogenic organisms—those believed to originate disease. But many of the supposed Saprophytic forms often described as originating disease are merely accidental associates, that is, living in companionship for a time.
Size.—In ordinary terms of measurement, bacteria are on an average from 1⁄25000th to about 1⁄5000th of an inch long. These measurements do not convey a definite impression to the mind. It is calculated that a thousand million of them could be contained in a space of 1⁄25th of an inch. The best impression of the size of the bacteria is, perhaps, obtained when it is stated that a 1⁄25-inch immersion objective gives a magnification of nearly 2,200 diameters, and that under this power the bacteria appear to be about the size of very small print. The standard of measurement accepted by bacteriologists is the micro-millimeter. One millimeter is equal to about 1⁄25000th an English inch. The number of micrococci in a milligramme of a culture of Staphylococcus pyogenes aurens has been estimated by Bujwid by counting at eight thousand millions. Not only do various species differ in dimensions, but considerable differences may be noted in a pure culture of the same species. On the other hand, there are numerous species which so closely resemble each other in size and shape that they cannot be differentiated by microscopic examination alone, and we have to look to other characteristics, as colour, growth in various culture media, pathogenic power, chemical products, &c., in order to decide the question of identity.
Reproduction.—The reproduction of bacteria takes place for the most part by fission and by spore formation. Fission is a process of splitting up or division, whereby an organism divides into two or more parts, each of which lives and divides in its turn. If certain organisms are watched under the microscope, a coccus or bacillus will be seen to elongate and at the same time become narrower, until its two halves become free, the two individual organisms again dividing and subdividing in their turn. This kind of reproduction is more readily seen in a higher class of unicellular organisms, the desmids. If, however, the new organisms do not break away from each other, but remain connected in groups or clusters, they are termed Staphylococci; if they remain connected in the form of a chain, or like a string of beads, they are termed Streptococci. If the division takes place in one plane, Diplococci are formed; if in two directions Tetracocci, or Tablet-cocci, are formed. On account of this multiplication by fission, the generic name of Schizomycetes, or fission-fungi, has been given to bacteria.
Spores.—A second method by which bacteria propagate is by spores. These bodies are distinguished by their remarkable power of resistance to the influence of temperature and the action of chemical reagents. Some of them will resist their immersion in strong acid solutions for many hours; also freezing and very high temperatures. Spore formation may take place in two ways: firstly, by “endogenous spores” (internal spores); secondly, by “arthrospores.”
Endogenous Spores.—When the formation of the spores takes place in the mother-cell, the protoplasm is seen to contract, giving rise to one or more highly refractive bodies, which are the spores. The enclosing membrane of the organism then breaks away, leaving the spores free.
Arthrospores.—When the spore is not formed in the parent bacillus, but when entire cells (owing to lack of favourable conditions of growth) become converted into spores, the formation is known as “arthrogenous,” the single individual being called an arthrospore. When the conditions are again favourable, spores germinate, giving rise to new bacilli. The germinating spore becomes elongated, and loses its bright appearance, the outer membrane becomes ruptured, and the young bacillus is set free. Certain conditions, such as the presence of oxygen in the case of the anthrax bacillus, give rise to the formation of spores; while various kinds of bacteria secure continuous existence by developing spores when there is lack of proper food material.
With reference to the incredible rapidity with which the bacteria multiply under conditions favourable to the growth and development, Cohn writes as follows:—“Let us assume that a microbe divides into two within an hour, then again into eight in the third hour, and so on. The number of microbes thus produced in twenty-four hours would exceed sixteen and a half millions; in two days they would increase to forty-seven trillions; and in a week the number expressing them would be made up of fifty-one figures. At the end of twenty-four hours the microbes descended from a single individual would occupy 1⁄40th of a hollow cube, with edges 1⁄25th of an inch long, but at the end of the following day would fill a space of twenty-seven cubic inches, and in less than five days their volume would equal that of the entire ocean.”
Again, Cohn estimated that a single bacillus weighs about 0·000,000,000,024,243,672 of a grain; forty thousand millions, 1 grain; 289 billions, 1 pound. After twenty-four hours the descendants from a single bacillus would weigh 1⁄2666th of a grain; after two days, over a pound; after three days, sixteen and a half million pounds, or 7,366 tons. It is quite unneccessary to state that these figures are purely theoretical, and could only be realised if there were no impediment to such rapid increase.
Fortunately, however, various checks, such as lack of food and unfavourable physical conditions, intervene to prevent unmanageable multiplication of these bodies.
These figures show, however, what a tremendous vital activity micro-organisms do possess, and it will be seen later at what great speed they increase in water, milk, broth, and other suitable media.
The following bacilli, among others, have numerous flagella distributed over the whole of the organism: the bacillus of blue milk (Bacillus cyanogenus)[52]; the bacillus of malignant œdema; the hay bacillus (Bacillus subtilis); Proteus vulgaris, &c.
The following have only one or two flagella at the poles: the Bacillus pyocyaneus, the Spirillum finkleri, the Spirillum choleræ Asiaticæ, &c.
The Spirillum undala, Spirillum rubrum, Spirillum concentricum, and Sarcinæ, pocket-cocci, have several flagella.
Micrococcus agilis have also several flagella; these possibly arise from one point. As I have already pointed out, the classification of the bacteria is one of great difficulty, since new kinds are being constantly discovered, and at present any attempt made in this direction can only be considered as quite of a provisional nature.
The difficulties which stand in the way may be surmised from the fact that Sarcinæ, pocket-cocci, were originally believed to be a single species, described by me, under the name of Sarcina ventriculi, in the fourth edition of my book, “as remarkable bodies invading the human and animal stomach, and seriously interfering with its functions.”
Fig. 268.—Sarcinæ.
The original woodcut of these curious parasites is reproduced in [Fig. 268], also in [Plate IX]., No. 7, and which evidently belong to a different species, numbering thirty-nine altogether. Quite recently Mr. G. H. Broadbent, M.R.C.S., Manchester, sent me a supply of these interesting bodies lately discovered by him in an infusion of cow manure. On examining a drop with a power of 1500 diameters they were discovered moving over the field of the microscope with a gyrating motion by the aid of flagella projecting from each corner of the pocket. After some days, having attained their full growth of four, eight or sixteen in a pocket, they break up, and recommence the formative process. Sarcinæ are certainly pathogenic in their nature. Cocci in groups, or asso-cocci, are similarly associated. These several forms of spiro-bacteria are enclosed in a transparent cell-wall, and are sometimes described as zooglæa.
Of bacteria the most characteristic groups are bacillus, bacterium, and a species of clostridium, a bottle-shaped bacillus. It is, however, difficult to draw a sharp line between so-called species.
Spiro-bacteria, or spirilla, possess short or long filaments, rigid or flexible, and their movements are accordingly rotatory, or in the long axis of the filaments. These bodies are again divided into comma bacilli, or vibrios—a name invented by the older microscopists who first described them—some species of which have a flagellate appendage, to which their movements are due.
Anthrax, Splenic Fever, has been long known to be prevalent among cattle at certain seasons of the year, and is believed to originate from peculiar conditions of climate and soil. This view of splenic fever on microscopical examination proved an entire fallacy. Bollinger in 1872 discovered that the blood of the affected animal was still virulent after death, owing to the presence of the spores of the bacillus, and that the soil also became infected and impregnated by the disease germs wherever the fever first broke out. In 1877 Dr. Koch made a more careful investigation into the source of the disease, and was able to give a complete demonstration of the life-history of the splenic fever bacillus, and to offer definite proofs of its pathogenic properties. He pointed out that the rods grew in the blood and tissues by lengthening and by cross division. Further, that they not only grew into long leptothrix filaments but they produced enormous numbers of seeds or spores. He watched the fusion of the rods to the formation of spores and the sprouting of fresh rods. He furthermore inoculated a mouse, watched the effect through several generations, and fully demonstrated that in the blood and swollen spleen of the animal the same rods were always present. Pasteur and Paul Bret pursued the same course of investigations, which were always followed with precisely similar results. It was, however, principally due to the researches of Koch that the doctrine of contagium vivum was placed on a scientific basis.
Subsequently Koch formulated methods of cultivation, and dictated the microscopical apparatus needful. Furthermore, he furnished postulates for proving beyond doubt the existence of specific pathogenic micro-organisms.
“The chain of evidence regarded by Dr. Koch as essential for proving the existence of a pathogenic organism is as follows:—1. The micro-organism must be found in the blood, lymph, or diseased tissue of man or animal suffering from, or dead of the disease. 2. The micro-organism must be isolated from the blood or tissue, and cultivated in suitable media—i.e., outside the animal body. These pure cultivations must be carried on through successive generations of the organism. 3. Pure cultivation thus obtained must, when introduced into the body of a healthy animal, produce the disease in question. 4. In the inoculated animal the same micro-organism must again be found. The chain of evidence will be still more complete if, from artificial culture, a chemical substance is obtained capable of producing the disease quite independently of the living organism. It is not enough to merely detect, or even artificially cultivate, a bacterium associated with disease. An endeavour must be made to establish the exact relationship of the bacteria to disease processes. In many instances disease bacteria regarded as the actual contagia have been found, on a further searching inquiry, to be entirely misleading. It is almost needless to remind the enthusiast that the actual contagion of the disease must be fully demonstrated.”
Fig. 269.—Micro-Photograph of Typhoid Fever Bacteria. Magnified 1000 ×. Taken by Leitz’s oil immersion 1⁄12-inch ocular No. 4, and sunlight exposure of one minute.
Typhoid Bacillus ([Fig. 269]).—Rods 1 to 3µ in length, and ·5 to ·8µ in breadth, and threads. Spore-formation has not been observed, but the protoplasm may be broken up, producing appearances which may be mistaken for spores. Actively motile, provided, some with a single and others with very numerous flagella, which are from three to five times as long as the bacillus itself. They stain readily in aqueous solutions of aniline dyes; and grow rapidly at a temperature of about 60° Fahr. In plate cultivations minute colonies are visible in thirty-six to forty-eight hours; they are circular or oval, with an irregular margin. On agar they form a whitish transparent layer, and they flourish in milk.
Fig. 270.—Plague Bacillus, Bombay, 1897. Magnified 1200 ×.
The Plague (Pestis Bacillus).—The Bombay plague of 1897-98 will ever be remembered as one of the most appalling visitations ever known. The number of deaths will never be accurately determined, as the native population, among whom the disease chiefly prevailed and became so fatal, concealed their dead or carried them away by night. The outbreak from the first proved to be most infectious, its incubation lasting from a few hours to a week only. It prevailed in all the over-crowded native quarters of the city. The rats and mice that infested the dwellings of the poor were found to be equally susceptible with human beings, and these vermin also died by hundreds. Those that survived left their holes and made off, in this way helping to spread the infective virus. On examining the bodies of dead rats, they were found to have swollen legs, the blood being filled by bacilli and curious monads, with whip-like appendages. The bacillus of plague was discovered by Kitasato in 1894; it is characterised by short rods with rounded ends, and a clear space in the middle. The bacilli stain readily with aniline dyes, and when cultivated on agar, white transparent colonies are formed which present an iridescent appearance when examined by reflected light. In addition to the bubonic swellings, the neighbouring lymphatic glands were also swollen and blocked by bacilli.
Fig. 271.—Monads in Rat’s Blood, 1,200 ×. (Crookshank.)
a. Monad threading its way among the blood-corpuscles; b. Another with pendulum movement attached to a corpuscle; c. Angular forms; d. Encysted forms; e and f. The same seen edgeways.
My illustration ([Fig. 270]) is from a micro-photograph taken in 1897, when the death rate stood very high. The general distribution of the bacilli, together with phagocytes and the contents of swollen lymphatic glands, magnified 1,200 ×, is from a preparation made in hospital. The monads from the rat’s blood, 1200 ×, seen threading their way among the blood corpuscles of a rat, and represented in [Fig. 271], are somewhat larger than those found in the Bombay rats, but the flagella in the latter were quite as marked, while the encysted forms were wholly absent and the blood corpuscles less crenated. The white bodies ([Fig. 270]) were in some preparations, together with the lymphatic bodies, more numerous and more swollen.
With regard to the conditions of life of the bacteria, they may be divided broadly into two classes. When the organisms draw their nourishment from some living body or “host,” they are known as “parasites.” These are further termed “obligate” parasites if they exclusively live on their “host.” If the bacteria draw their nourishment from dead organic matter, they are called “saprophytes.” These are also divided into “obligate” and “facultative” saprophytes. Thus it will be apparent that a parasite under certain circumstances may readily become a saprophyte.
Some of the more important saprophytes are those organisms which play an important and useful part in our every-day life, such as, for instance, in the phenomena associated with fermentation, and putrefaction agents which transform dead and decomposing organic matter into their simpler elements, thus completing the great life cycle, and rendering the dead and effete matter again ready for the vital processes.
Among other life manifestations of certain bacteria may be mentioned those which have the property of generating colouring matter, though not chlorophyll. The bacteria themselves are colourless and transparent, and the pigment is merely formed as a product of their metabolism, especially under the influence of light. Many of the bacteria give rise to various gases and odours, particularly the anærobic organisms, which originate those foul putrefactive gases (ammonia, sulphuretted hydrogen, &c.). The blood-rain, Micrococcus prodigiosus, gives off an odour resembling trimethylamin. Micro-organisms have the property of producing various changes in the medium on which they are grown. In many cases albuminous bodies are peptonized and gelatine is liquefied. Many bacteria have the faculty of resolving organic bodies into their simplest elements; others, again, have the property of converting ammonia into nitric and nitrous acid. Certain microbes have the property of becoming phosphorescent in the dark. These phosphorescent bacteria are often seen on decaying plants and wood; sometimes in tropical climates the sea becomes luminous owing to the presence of countless numbers of these organisms. Again, they are frequently seen on the surface of dead fish, particularly mackerel, which often become so bright as to strongly illuminate the cupboard in which they lie.
The particular class of fungi that produce disease in man and the higher animals are generally known as “pathogenic.” These pathogenic organisms may exert their pernicious power in several ways. They may be injurious on account of their abstracting nourishment from the blood or tissues, or for the purely mechanical reason of their stopping up the minute capillaries and blood-vessels by their excessive multiplication. But the poisonous action of most of the pathogenic bacteria is due to the chemical products secreted by the organisms, and it is to the circulation and absorption within the body of these poisons that the disturbances of the animal system, which characterise disease, decay, and dissolution of every organism, must be traced.