DIAGNOSIS OF TUBERCULOSIS.
It is needless to repeat the various symptoms of tuberculosis according to its different seats and the degree of its extension in the animal body. In cases in which the indications are slight, greater importance may be given to them through the knowledge of the existence of more advanced or decided cases in the same herd, or the necropsies of animals taken from it. Yet in the average herd it is safely within bounds to say that three fourths of the affected cattle will escape condemnation if we employ objective symptoms alone. In one herd of seventy head, in which the tuberculin test condemned twenty-four head (being 50 per cent. of the mature animals), I left the examination after slaughter to the veterinarian of the A. J. C. C. who was at the time skeptical as to the value of the tuberculin test. He wrote me afterward of his surprise at finding every one of the twenty-four condemned animals tuberculous, when not one of them had shown symptoms by which he could recognize the disease in life. This is no exceptional case, and may be advanced rather as a typical example of the ordinary infected country herd.
Microscopic detection of the bacillus in the expectoration may be successful in the horse with pharyngeal or pulmonary tuberculosis, but fails in those forms that affect the other internal organs. It is all but useless for the expectoration of cattle and dogs. When there is cutaneous tuberculosis or a tuberculous fistula this is much more valuable, and it is especially useful in dogs and parrots.
The precipitate in the centrifuge will often show the bacilli that are present in milk, but in very many cases of tuberculosis the bacilli are not present in the milk.
The centrifuge used on the urine may also succeed when kidneys, bladder or prostate are affected, but the bacilli are rarely found in the absence of disease of these organs. The smegma bacillus is a source of fallacy.
The serous effusions in the affected serosæ (pleura, peritoneum, pericardium, synovial cavities) may also be centrifuged and the presence of the bacilli revealed.
The agglutination test of Arloing and Courmont though often giving positive results, (95.5 per cent. in pulmonary tuberculosis, 50 per cent. in surgical, Arloing and Courmont; 40 per cent., Knopf; 25 to 50 per cent., Lartigan); yet proved too unreliable, and frequently gave positive results when tuberculosis was absent. The best medium for cultures to be so used is 6 per cent. glycerine bouillon, and the age of the tuberculosis culture 8 to 12 days. One part of fresh blood serum of the suspected animal in a sterilized capillary tube is added to ten parts of the bacillus culture, and the tube placed in an oblique position. In 2 to 24 hours a fine sand-like material precipitates along the sides of the tube, and the microscope shows the bacilli in clumps, absolutely still without even Brownian movements. Gallemaerts found that it proved very satisfactory with the serum of Guinea pigs after three days from intraperitoneal inoculation, was less marked after inoculations subcutem, and that in man the agglutination appeared in influenza and pneumonia in the entire absence of tuberculosis. Such an uncertain test cannot be utilized in veterinary sanitary work.
Experimental inoculation with milk, expectoration, morbid discharges, the scraping of nodules, etc., is much more searching, and will detect more cases than the microscopic examination. But it fails entirely in cases in which the milk of unquestionably tuberculous animals is free from bacilli, or in which the local nodule or discharge tested is itself free from tubercle. It is a test of the local lesion and not of the entire animal system.
In choosing a subject for inoculation, the first consideration is that it must come from a healthy stock and be itself free from tuberculosis. Next, it must be of a species actively susceptible to the habitual tuberculosis of the animal from which the inoculated matter is taken. Thus for man, ox, dog and parrot, the Guinea pig is especially appropriate, while for gallinaceæ and horses, the rabbit is to be preferred. Inoculation is usually made into the peritoneal cavity.
As a period of two or three weeks is usually necessary to allow of an extensive development of tuberculosis, the method must be too often discarded on account of the delay in obtaining results.
Tuberculin test. Many stock owners still entertain an ignorant and unwarranted dread of the tuberculin test. It is quite true that, when recklessly used by ignorant or careless people it may be made a root of evil, yet as employed by the intelligent and careful expert it is not only perfectly safe, but it is the only known means of ascertaining approximately the actual number affected in a given herd. In most infected herds, living under what are in other respects, good hygienic conditions, ⅔ or ¾ are not to be detected without its aid, so that in clearing a herd from tuberculosis and placing both herd and products above suspicion the test becomes essential.
Tuberculin is the bouillon in which the tubercle bacillus has been grown, charged with the toxic products of its growth, but which has been raised to a boiling temperature to destroy all germ life, and from which the dead germs have been removed by passing it through a porcelain filter. When a physiological dose of this has been injected, subcutem, into the suspected animal, it has no effect on the non-tuberculous, while in the tuberculous it produces, in the course of the next 24 hours (usually from the 8th to the 16th), a steady rise of temperature by 2° F. or more, followed by a slow subsidence to the normal. This may last for from three to ten hours in different cases.
Among the precautions may be named:
1. The temperature of the animal is best taken at intervals, or at least, morning, noon and night, on the day preceding the injection to see that the animal shows no habitual rise at any time of the day. Yet in busy field work the one night temperature taken just before injecting will rarely fail to give a satisfactory normal as a standard for the animal. Any quotidian rise almost invariably reaches its climax at night.
2. The subject must be in good general health. If there is present in the system any concurrent disease it may undergo an aggravation within twenty-four hours and give a rise of temperature that will be mistakenly set down for tuberculosis. At the very start, therefore, it is important that the general health of the subject should be first assured by a critical professional examination. If some other disease is present the tuberculin test had best, as a rule, be delayed until that has subsided, while if tuberculosis is found the test will be superfluous.
3. The subject must not be within three weeks of parturition, nor about to abort. In many cases, though not in all, as preparations are made for calving, the system becomes unduly susceptible to the presence of tuberculin and that agent will cause a rise of temperature, though no tuberculosis is present. Unless this source of error is carefully guarded against the most valuable cows in the herd may be condemned unjustly.
4. The cow must not be within three days of the period at which “heat” would naturally occur. Under the excitement of œstrum the body temperature usually rises two or three degrees, and if tuberculin has been used this rise may be attributed to tuberculosis and a sound animal may be condemned. Nor is it always enough that the animal is supposed to be pregnant. Abortions sometimes take place unexpectedly and unknown to the owner. If, therefore, a cow under the test and which is not well advanced in pregnancy should show a rise of temperature it should be at once ascertained whether the animal is not in “heat.” If symptoms of “heat” are found she should be set aside along with any calving cows to be tested again when such a source of error is no longer present.
5. The tested animal must not be exposed to a hot sun in a closed area. In excess this will cause heat apoplexy, and the fever heat which ushers this in, may easily be mistaken for the indications of tuberculosis.
6. Cattle taken from pastures must not be enclosed in a hot, stuffy stable. While they must be tied up to allow of the temperature being taken at short intervals, coolness and ventilation should be secured in summer by a sufficient air space and the requisite ventilating openings.
7. Exposure to cold draughts between open doors and windows, or to wet or chilly blasts out of doors should be carefully guarded against. A chill proceeding from any source and alike in the presence or absence of tuberculin causes a rise of the internal body temperature.
8. Heavy cows unaccustomed to stand on hard boards may have a rise of temperature in connection with resulting tenderness of the feet. One must avoid hard floors on the day of the test or make examination of feet and allow for attendant fever.
9. Omission of the previous milking or a change of milker and consequent retention of part of the milk will raise the temperature of a nervous cow, and in careless hands secure an erroneous condemnation.
10. Privation of water at the regular time will often cause rise of temperature especially when on the dry feeding of winter. I have seen a general rise of two degrees and upward from the delay of watering for a single hour, while after watering the temperature went down to the normal and remained so. Water always tends to a temporary lowering of temperature but in the presence of tuberculosis it soon rises again.
11. Change of food is liable to produce a slight indigestion and rise of temperature. This should be avoided as far as possible, and when a herd is taken up from pasture for the test, it should have grass, ensilage or other succulent food.
12. Cattle just from a long journey by road or rail, or other cause of violent exertion are liable to have an elevated temperature from the leucomain poisoning. Such should be left at rest until the transient fever shall have subsided.
13. Violent handling of nervous cows in taking the temperature must be carefully avoided. The operator who cannot handle them gently is not fit for this work.
14. There must be evidence that the animals have not been repeatedly tested at short intervals shortly before. In a number of instances I have found a proportion of the cattle irresponsive to tuberculin, though a post mortem proved the presence of tuberculosis. Unscrupulous men, wishing to sell on a guarantee, can avail of this in animals so unaffected by the test.
15. The operator must have absolute control, even of the feeding and watering of the animals on the day of testing. Otherwise the rise of temperature may be prevented by a liberal use of antipyretics and a false guarantee may be secured.
16. An unthrifty animal, having general symptoms suggesting tuberculosis, must be subjected to the most critical examination in addition to the tuberculin which in such animals often fails to cause hyperthermia. Fortunately in such animals the tubercles are usually numerous and extensive enough to be discovered through objective symptoms.
17. Animals excluded from the test by reason of some individual unfitness at the time (parturition, œstrum, abortion or any other disease) must be marked and held for the test later after such disqualification shall have passed.
18. The operator must bear in mind the possibility of transferring other diseases from animal to animal, by contact, by the use of the same hypodermic needle on two in succession, and above all by the clinical thermometer. Diseases like contagious abortion, which present no obvious symptoms in the intervals, are especially liable to be carried in this way, and instances of the active extension of this after a test, have come under my notice. The operator should always enquire carefully as to the existence of abortions and sterility in the herd, put the aborting animals by themselves, using a special thermometer upon them, and carefully washing the hands before going to other cattle. It is well further to clean the thermometer after each animal and disinfect it with carbolic acid solution (5:100).
Dose of Tuberculin. Of the usual American preparation 2cc. (30 drops) is adapted to a cow or ox of 1,000 to 1,200 pounds. For larger and smaller animals a moderate encrease or reduction must be made, yet a considerable latitude is allowable. The new-born calf will take five drops and the animal of 700 pounds 25 drops.
Technique of the Operation. Lapses are so easily made when dealing with a large herd and are so dangerous that a regular plan should be systematically followed. The following will be found simple and convenient:
1. Inject the herd at 10 or 11 P. M. to secure a good rest and be fresh for the rise of temperature early next morning.
2. Before injecting have the subjects arranged in order and record them by name or other means of identification, with age, sex, breed, weight, pregnant or not, past or prospective date of calving, abortion, indications of disease, temperature taken just before injection and appropriate dose.
3. Inject into the loose connective tissue on the side of the neck, the animal being held by the nose, if necessary, by an assistant.
4. Use a syringe which has not been employed for any infectious products, and see that it is thoroughly cleansed and disinfected by boiling or by filling it with a carbolic acid solution (5:100).
5. After drawing the appropriate dose into the syringe, wipe the nozzle and dip it in strong carbolic acid before inserting it into the skin. This safely disinfects any virulent matter that may be lodged on the surface of the skin, and obviates those infected swellings and abscesses that have been a cause of complaint by stock owners.
6. When the nozzle is withdrawn from the skin, wipe it and dip it again into the strong carbolic acid to prevent any risk of infecting the tuberculin into which it is to be plunged.
7. The nozzle is much more easily inserted in the skin if the latter is pinched up so that the needle will transfix it at a right angle, instead of passing through a greater amount of the dense tissue because of the oblique direction. An excited animal with a thick, tense hide and a contracted panniculus muscle will offer serious obstruction which lessens greatly as the subject gets over its excitement and the muscle relaxes.
8. Temperature should be taken at 6 or 7 A. M., eight hours after injection of tuberculin, and every two hours thereafter, until the sixteenth hour.
9. If any subject shows no rise of temperature until the 16th hour after injection, its examination may be discontinued, but if it shows a slight rise toward the 16th hour it should be continued until it has shown a distinct reaction with steady rise and fall, or until, without such distinct reaction, the temperature descends to the normal.
10. If one has shown a distinct reaction but is still rising at the 16th hour, it should be continued till it begins to fall. The typical reaction is one in which the rise and fall are both gradual, and extend over a number of hours.
11. In recording the temperatures, there should be noted the exact time of each feeding, watering and milking, or any other condition (change of weather), which may in any way affect the heat production or radiation.
12. In old, emaciated animals and in second or third tests, Pearson uses twice the usual dose of tuberculin or more.
Tuberculosis Reaction. With slight variations different operators make their estimate of tuberculosis reaction on nearly the same general basis. A rise of 2° F. over the highest temperature of the day or days before, in the absence of any other appreciable cause, and provided that the elevation has followed the tuberculosis type of gradual rise and fall, is held to condemn. If, however, this rise does not exceed the normal average, if the temperature before injection did not exceed 100° and that after injection 102°, the case may well be held in doubt and reserved for re-testing. If, on the contrary, the initial temperature of the animal was 103°, and there was, between the 8th and 16th hours, a gradual typical rise and fall, reaching 104° or a little over, in the absence of any other cause for this, the subject would be condemned. Cattle having an initial temperature of 103° or above are not favorable subjects for the test, except in the case of calves in which the temperature is normally higher and the reaction must reach a higher point. In all cases of doubt it is well to hold for a second test, unless urgent sanitary considerations demand that a herd should be freed from the infection in short order. Then it may be better to risk a single error, with the concurrence of the owner, than to leave a possible centre of infection in the herd.
Local swelling in the seat of injection may be charged to lack of antiseptic care, or the presence of septic germs in the system of the animal prior to injection.
A chill during the period of reaction is not uncommon, especially in cold weather, or in a draught of cold air. The coat may stare along the spine in patches, or generally, tremors may be seen on the body or limbs, and a clammy coldness invades the ears and horns, and especially the points of the hocks and ischia. The back is sometimes arched and the feet drawn together somewhat.
In the absence of any source of excitement the head may be less elevated, the ears lopped forward or drawn back, and even the eyelids may droop somewhat. These phenomena may last for a few minutes or for an hour or two.
In testing other genera consideration must be had of the different normal temperature (horse 99.5°, dog 98.5°, sheep or pig 103°, bird 106°), and the varying susceptibility to tuberculin, the Guinea pig requiring a maximum dose relatively to its size and man or horse a minimum.
Effect of Tuberculin Test on the Later Average Health of the Animal Reacting. The transient fever and reaction on the day after injection modifies the milk secretion temporarily to a certain extent in ratio with the hyperthermia. The consensus of veterinarians of the largest experience, and the voice of the International Veterinary Congress at Berne in 1895, oppose the doctrine of any continuous effect on the health even of the tuberculous. Yet in the case of Governor Morton’s large herd of Guernseys a careful record of temperatures showed that for weeks after the test the reacting animals presented oscillations which were not shown before, and which were not found to occur in the sound animals. In the activities of sanitary work such indications are easily missed.
Effect of Tuberculin Test on Sound Animals. In 1894 I tested this on a number of thoroughbred Jersey and grade cows, injecting them six times at intervals of from five to fourteen days. It led to no appreciable change of the general health as shown by the temperature, breathing, pulse, yield of milk or its quality. Careful analysis was made of the milk at each milking, and in two animals soundness was attested by post mortem examination. Similar tests made by the Bureau of Animal Industry and others led to the same results. Cows in which the yield of milk was on the gain continued to encrease in the same ratio as those that had not been injected, and those in which it was on the wane showed no more rapid decrease. The butter fats and total solids showed no variation more than appeared in the healthy.
Action of Tuberculin on Parturient Cows. The testimony of Bang, Eber and Pearson, based on a very extensive experience, would indicate that the tuberculin test is not forbidden by the parturient condition. Eber concludes that unless the initial temperature materially exceeds 39.5° C. (103° F.) the parturient state is no barrier to successful testing. My own experience, on the contrary, is that a considerable proportion of parturient cows give a reaction when the initial temperature did not exceed 103° F., and when no sign of tuberculosis could be found. As an example, a cow in high condition, with an initial temperature of 102.8° F., rose gradually from the eleventh hour after injection and reached 106.3° by the eighteenth, a rise of 3.5°. From the record she was not due to calve for three months, but a fortnight later, when already killed and laid open, she showed all the signs of parturition, a fully matured calf, and not a trace of tubercle. This is far from unusual, and I am convinced that many errors will be avoided by refusing to condemn parturient animals or those within a couple of weeks before or after parturition on the tuberculin test alone.
Reliability of the Tuberculin Test. Even in the most careful hands the tuberculin test cannot be held to be infallible. A certain very small proportion of cows react without the recognition of any tubercle post mortem, some because of other bodily conditions, like parturition or abortion, but in skilled hands these may be ignored in ordinary sanitary work. Pearson claims to have had but 8 such cases in 4400 cows that gave a typical reaction. He suspects that some of these even had undiscovered tubercle, and Nocard thinks that all such cases are to be explained in this way. On the other hand a very few really tuberculous animals fail to react, some in connection with advanced disease, some because of repeated previous testing, and some because of the introduction of antipyretic agents into the system, but such cases can either be detected and controlled or are so infinitesimal in numbers, that they can be safely ignored in sanitary work. In skilled hands, the tuberculin test will show at least ⁹⁄₁₀ths of all cases of tuberculosis, when other methods of diagnosis will not detect ⅒th. See above case of herd where objective symptoms showed nothing, yet tuberculin condemned half the mature cattle, and post mortem confirmed this, the skeptical veterinarian being judge.
The Relation of the Bacillus Tuberculosis of Man to that of Cattle. On the discovery of the bacillus tuberculosis it was largely assumed that it was the same in all tuberculous animals, in all organs and in all circumstances. But it was soon found that the bacillus of chicken tuberculosis differed materially from that of the mammalian, that it could be inoculated only with difficulty on cattle or Guinea pig, as could that of the latter on the bird. The bacillus of the chicken found a most receptive home in the rabbit and horse, and was more easily started in artificial culture in glycerine bouillon, than was that of man or ox. But presently it appeared that the affinities and disparities did not end here. The bacillus from man or ox led to much more pronounced lesions in Guinea pigs than in rabbits, and the abdominal bacillus of the horse was inoculable on the chicken. Both horse and parrot proved receptive to the bacillus from man. Swine, like Guinea pigs showed a receptiveness to the bacillus of man or ox. The bacilli from the sputum, open tuberculous sore, or bones of man showed less virulence for Guinea pigs and rabbits than did those from tubercles in the human lungs and liver. The bacillus from the ox showed a greater virulence toward rodents and other small animals than did the bacillus from man. The bacillus of human sputum inoculated on the ox did not habitually cause generalized tuberculosis, but oftentimes a local tubercle or group of tubercles, and sometimes the inoculation wound healed without permanent lesion. These last points were seized upon to sustain a doctrine of probable duality for the microbe of tuberculosis, but if duality it was quite evident it could not end there, but must be extended to multiplicity, each small group of genera having a tubercle bacillus peculiar to itself. Those who thought their interest lay in arresting all sanitary control of tuberculous cattle and their products, became urgent in opposition to active government measures, demanding mathematical proof of the infection of man from cattle, under conditions that would exclude the remotest possibility of the introduction of infection from another source. The clearest and most abundant circumstantial evidence would not suffice, they must have direct experimental inoculation under conditions of precaution against outside germs, which were practically impossible in any community, conveniently ignoring that such inoculation, if successful, would have amounted to manslaughter, and that no such experimental evidence has been had, or can be had, of any of the deadly diseases of man. Infection by exposure and accidental inoculations can be had in abundance, just as they can in tuberculosis, but never under the rigid precautions which would exclude the possibility of extraneous infection.
The subject has assumed such importance that I may be excused for introducing a portion of my paper read before the New York State Medical Society in 1900.
1. This Variability is Common to Microbes Generally. Certain bacilli, like those of anthrax, grow in the living body as rods only, but become long filaments in given artificial media. They produce no spores in the living tissue, but do so readily in the carcass or soil. Transferred from ox to ox they are generally fatal, but if grown for several generations in Guinea pigs, and then transferred to cattle, the resulting disease is slight (Burdon-Sanderson, Duguid, Greenfield). Rabies passed from dog to dog is almost constantly fatal, but if passed through the ape and then back to the dog it is comparatively harmless (Pasteur). In both these cases the inoculated animals become immune from the more virulent germs, showing that they have passed through the actual disease in an unusually mild form. The later system of Pasteur is founded on this same general truth, as are also the methods of lessening the pathogenesis of germs by subjecting them to compressed oxygen, to graduated heating, to an altered chemical condition of the culture medium, to antisepsis, etc. For a time such weakened cultures often retain their lessened pathogenesis, even through a succession of cultures in a susceptible animal body, acting as if the germ were indeed a distinct species. But it might well have been considered that a microbe which had changed its aptitudes in a given environment could presumably revert to its original habits under the incentive of a suitable medium. And this is precisely what does take place. Pasteur has shown that the less potent rabic virus becomes more potent when passed several times through the body of a rabbit, and that the weakened anthrax germ acquires greater force when passed through a series of small birds or newly-born mammals.
To come to tuberculosis, Trudeau tells us that a culture of bacillus tuberculosis from man inoculated on the rabbit, and then cultivated for two years in vitro, becomes much less destructive to Guinea pigs, and that after six years of such artificial culture all the Guinea pigs inoculated with it live for many months, some for two and a half years, and some even recover. The usual life of the Guinea-pig after inoculation is seventeen days.[[3]] All of our zymotic diseases have in a similar way cycles of malignancy and benignancy. For a series of years measles, scarlatina, diphtheria, smallpox, or grippe have an unwonted mildness, and, again, one or another merges into a cycle of extreme and fatal malignancy. Rinderpest on the steppes of Asia is comparatively harmless to the native stock, but among outside cattle imported into the steppes or attacked in their native lands it is habitually fatal. Texas fever is mild among the indigenous cattle in the Gulf States, but very deadly to Northern stock. Glanders is not at all fatal to horses of the plains, the Rockies, or the Sierras; but it becomes redoubtable when these horses carry it to the Eastern seaboard, and still more so in Western Europe. It is a common experience to see a malady transformed through the effects of heredity or acquired immunity, through environment or the temporary mitigation of virulence in the germ; and again we see the same disease, no longer restrained by such inhibitory conditions, bursting forth as a malignant and deadly plague. We have, therefore, no warrant for the hypothesis that a pathogenic germ which, under given conditions of life, has lost in pathogenesis, but not in vitality, should continue forever to exist as a harmless microbe.
[3]. Johns Hopkins Hospital Reports, Bulletin 100.
2. Varying Malignancy of the Tubercle Bacillus in Man. Nothing is more familiar to physicians than the slow progress of tuberculosis of the lymph-glands and bones, on the one hand, and its frequent rapid progress in pulmonary, abdominal, or encephalic organs on the other. It has on this account been rather difficult to persuade many of the etiological identity of scrofula and consumption. In experimental tuberculosis the same truth constantly crops up. Arloing and his followers found that the tubercle bacillus from the lymph-glands of man proved less virulent and deadly than that from the human lungs (Lecons sur la Tuberculose). As early as 1880, Creighton drew attention to this in his work on Bovine Tuberculosis in Man.
But the bacillus from the lungs is subject to variations of this kind. Among seven specimens of human sputum, cultivated by Theobald Smith, six had a fair average vitality, while the seventh failed to perpetuate itself on dog serum.[[4]]
[4]. Journal of Experimental Medicine, 1898, No. 111.
It should be strongly emphasized in this connection that the failure of extension and generalization of the sputum germ when transferred to cattle does not distinguish it from the tubercle bacillus as conveyed from ox to ox. Everyone at all experienced with the tuberculin test well knows that in most herds the majority of the tuberculous animals show no generalization, but only a localized tuberculosis. There is reason to believe that even recoveries take place after slight infection, and it is certain that many tuberculous cattle continue for years in what appears to be good general health. Unless in particularly susceptible subjects or under specially poor hygienic conditions, or unless in case of reinfection, the average bacillus of bovine origin habitually fails to produce in other cattle a rapid extension and generalization.
3. Interchangeability of Bacillus of Man and Bird. Of all known forms of tubercle bacillus that of birds is the most distant from that of man or ox, and yet the beautiful experiments of Nocard[[5]] serve to establish their essential identity. Taking the bacillus of human sputum, which would not infect the fowl, he enclosed it in collodion capsules, which confined the bacilli while allowing transudation of the animal fluids, and left these in the abdomen of the chicken for not less than four months. He repeated this three times in succession with the product of the original sputum germ, and obtained a bacillus which was actively pathogenic for the chicken, though it had been harmless after the sojourn of four and eight months respectively.
[5]. Annales de l’Institut Pasteur, September, 1898.
This may explain the reported cases in which a flock of poultry have developed tuberculosis a few months after they were placed in the hands of a consumptive caretaker. That such transmission does not always occur is not surprising, considering that transmission between man and man is infrequent in comparison with the number of exposures. So in cattle the majority of exposed animals usually escape, although in such a case there can be no plausible explanation on the ground of a difference of germ. We have in every case to consider the necessity for receptivity as well as infectivity, and the lack of either is a bar to infection. When, however, we assume that the most diverse tubercle bacilli are descendent’s of one original stock, that a large herd must furnish some animals of more than usual susceptibility, and that such animals are subjected to continuous accessions of both bacilli and toxins, we can easily understand how some of the more adaptable germs will in time accommodate themselves to the new medium. A Pettinkoffer, with an immune constitution or a specially vigorous gastric digestion, may with impunity drink a culture of cholera spirillum, but the same is not true of the drunkard fresh from a spree and with seriously impaired digestion.
Bacillus Tuberculosis in Man and Ox. Points of Similarity. The bacillus tuberculosis of cattle is in general shorter and thicker than those of man, but many in both subjects are morphologically indistinguishable. Such differences are often far exceeded by different specimens of one stock of germ seeded on different media. There is no great difference in the thermal death point, and the viability in light, dryness, cold and putrefaction. The tendency is in all cases to colonize the lymph plexus or glands and to develop the specific lesions, with slight variation in detail. The slow development of the lesions from both forms of bacilli and their histological similarity is another argument for their essential identity. The slow growth of both on artificial media, the demand of each for a medium having the same approximate composition, and the similar pathogenic and diagnostic characters of the toxic matters elaborated by both germs bespeak a primary identity. The very remarkable staining qualities of tubercle bacillus, from whatever source it may be drawn, are no less remarkable.
Tuberculosis of Man and Ox Coextensive. The prevalence of tuberculosis in man and ox in the same country and district is so frequent that it may be safely set down as the rule. Among ichthyophagists and great fishing communities, like the people of the Hebrides, Iceland, Newfoundland, Greenland, and the coasts of Hudson Bay, tuberculosis is rare. In these countries cattle are few or absent, or, like the hardy highland kyloes of the Hebrides, they are kept in the open air. The immunity of the people is not due to insusceptibility, since they fall ready victims to tuberculosis when removed to infected countries and cities.
In Northern Sweden, Norway, Lapland and Finland, where cattle are scarce and reindeer plentiful, tuberculosis is said to be rare, though the inhabitants live in the closest of dwellings through the long winter. In most of the Pacific islands there are no cattle, and the natives are comparatively free from consumption. In Hawaii, since the introduction of cattle, consumption has increased. Australia and Tasmania, which forty years ago were the great resorts for English consumptives, have become increasingly the homes of infection since the development of the cattle industry and the influx of phthisical subjects. Minnesota and Dakota, in the early days, were held to be incompatible with tuberculosis, but since the advent of the white man and his stabled herds they have largely lost their sanitary reputation. The highest known mortality from tuberculosis to-day is that of the reservation Indians of these States, who feed on raw, diseased beef. In the Kighiz steppes the Tartars subsist on the flesh and milk of their solipeds, and largely escape consumption. In Japan, Dr. Ashmead tells us that the common people escape tuberculosis, while the aristocracy suffer severely. He attributes this mainly to the debauchery of the ruling class; but it must not be overlooked that they eat freely of beef and dairy products, which the rice-eating poorer population do not. The same remarks apply in measure to the mandarin and plebian classes in China. Holden tells us that tuberculosis is rare in Columbia, Ecuador and on the eastern slopes of the Andes, where little or no milk or butter is used. It must be further borne in mind that in these countries all herds live in the open air, and practically escape infection.
These examples must be contrasted with the consumers of beef and milk in civilized temperate countries, where the stock are largely kept indoors. A general average mortality of 7 or 8 per cent. from tuberculosis, and the post mortem evidence in European and American hospitals of 33 to 50 per cent. which show tubercular lesions, recent or remote, cannot be lightly passed over. The contrast with our reservation Indians is still more striking. Holden and Treon testify that the meat furnished to the Indians is always poor and often diseased, and that when the stock arrives our hungry wards devour the internal organs raw, or, later, the flesh as pounded preserved meat, and still uncooked. The deaths of these Indians from tuberculosis is 50 per cent. of the total mortality.[[6]] Dr. Washington Matthews, who spent twenty-one years among the Indians, gives their food as the main cause of the disease, and states that when the supply of fresh meat is liberal the death rate from tuberculosis is highest (Census of 1880).
[6]. Medical Record, August 13, 1883.
If we now contrast this fearful mortality with the immunity of the Indians of Hudson Bay, Great Slave Lake, Alaska, and the North generally, we have a most suggestive picture. It may be conceded that the extreme Northern Indians, being beyond the cereal region, have a slight measure of protection in their meat diet; but the recent spread of tuberculosis, like a plague, among the inhabitants of Barrow Straits, when introduced by the frozen-in whalers and the relief party, is sufficient disproof of any claim of special insusceptibility. There can be no doubt that in this, as in other virulent diseases, the rule holds that the long absence of the infection secures the preservation of the susceptible lines of blood, so that when the contagion does come it finds a more inviting field than in countries in which the more susceptible strains have been killed off and the comparatively immune have survived. Toward the Arctic circle the Indian must crowd into closer quarters in winter than his brother further south; but, in spite of all, the beef-eating Indian is being rapidly exterminated by tuberculosis, to which his brother of the north is a comparative stranger.
Exceptions: Their Explanation. This statement would be incomplete without a notice of exceptions to the rule. The Cape Town branch of the British Medical Association reports “that tuberculosis is rapidly increasing there in the human population, while tubercle in cattle is almost nonexistent.” This finds an abundant explanation in the different conditions of life. The men live indoors and concentrate the infection, whereas the cattle enjoy an outdoor life and escape. In a latitude of 30° south, where frost is rare, and with a dry climate (12 to 30 inches of rain per annum), the colonists find no occasion for housing their cattle, so that the conditions for the prevention of tuberculosis are ideal. It may be added that cattle are far less numerous in Cape Colony than they formerly were. The destruction first by lung plague and later by rinderpest has made the cattle industry extremely hazardous, and even before the advent of the rinderpest many had abandoned cattle and taken to sheep.
Parallel cases can be found in other countries. In Egypt, the great resort of consumptives, cattle are almost immune, the abattoirs furnishing about one tuberculous ox in ten thousand killed.[[7]] From Tunis (Alix), Algiers (Sarciron, Plaise), and Senegambia (Lenoir) a similar testimony comes. Cattle imported from Europe may die of tuberculosis, which is liable to assume a rapidly fatal type; but the native cattle, kept in the open air, are practically exempt.
[7]. Danzon. Études Expérimentale et Cliniques sur la Tuberculose, vol. i. p. 350.
Jersey cattle in their native island, staked out at pasture all the year round, show little or no tuberculosis, whereas the housed Jerseys of England and America suffer severely. The cattle of our Gulf Coast States, kept on ranches in the open air, are largely immune, and the cattle of Columbia, Ecuador, Peru, and the Argentine Republic largely escape; but the housed dairy cows of our Southern cities show a very high ratio of consumptives. Consumption becomes more and more deadly in the Southern negro even in the country localities, while the outdoor cattle of the same districts escape.
The absence of tuberculosis from the sanitarium herd at Saranac requires to be explained on a different basis. This herd is housed in winter, and infection, once introduced, would have opportunity to spread. The absence of tuberculosis is highly complimentary to the management of the establishment. But a similar immunity is the rule for all well-managed sanitariums, and not as regards cattle only, but man as well. At Argeles no case of tuberculosis contagion to attendants occurred in ten years (Ferrand). At Soden baths, in a village of 1500, there were in thirty-four years 65 deaths, 15 from consumption (Hopt). At Falkenstein, in fifteen years, one attendant became tuberculous (Jousset). At Görbersdorf the cases of consumption in the village and environs decreased (Knopf). At Brompton, London, in thirty-six years, among 150 attendants, but one became consumptive, though they individually served for from fifteen to twenty-four years, and nearly 40,000 patients had been received.[[8]] A well-conducted sanitarium is and should be a safer place than the average community, in which 15 per cent. and upward are tuberculous. The educational influence of such an institution should decrease tuberculosis in the surrounding districts.
[8]. Études Expérimentale et Cliniques sur la Tuberculose, vol. iii. p. 408.
Cases of Direct Infection from Man to Ox. Chauveau induced tuberculosis in cattle by feeding the tubercle from the lungs of man.[[9]]
[9]. Arloing. Tuberculosis Congress of 1891.
Nocard relates that a Beauce farmer, with a finely appointed stable and healthy herd, in 1883 employed a dairyman who had cough, profuse expectoration, and occasional hæmoptysis, and who had been several times in the hospital in consequence. He slept in the cow stable directly over the cows. In 1886 two cows, stalled immediately beneath him, showed ill health and were put up to fatten, but did badly and showed extensive tuberculosis when butchered. The dairyman stayed until 1891, having to go to the hospital several times in the interval. In 1892 the tuberculin test was applied and seven more cows were found to be tuberculous.
Huon tells of a cow bought to furnish milk for calves used to raise vaccine. She stood the tuberculin test, and was carefully secluded from all other cattle, but soon began to fall off, and in six months was very much emaciated, responded to the tuberculin test, and when killed showed extensive tuberculosis. Her caretaker at the vaccine establishment had what was believed to be chronic bronchitis, but when he died, soon after, this was found to be extensive pulmonary tuberculosis.
Bollinger inoculated a three-months’ calf with liquid from human tubercle and killed it seven months later. Fibroid pedunculated tumors, from a pea to a walnut in size, hung from the mesentery and spleen, and the mesenteric and retroperitoneal glands were tubercular.[[10]]
[10]. Münchener medicinische Wochenschrift, 1894.
Sidney Martin furnishes the following: Four calves were fed 70 c.c. of sputum containing a large number of bacilli. Three were killed after four, eight, and twelve months respectively, and had severally 53, 63 and 13 nodules on the small intestine, mostly on Peyers’ patches. Two calves received at one dose 440 c.c. of tuberculous sputum, and were severally killed after eight and nineteen weeks. The first had tubercular nodules in the intestine and mesenteric glands.[[11]]
[11]. Report of Royal Commission of 1895.
Frothingham injected into the peritoneum of two calves, three and thirteen weeks old, a culture of tubercle bacilli isolated one year before from the liver of a child. Slight local nodules were produced, some like spontaneous tubercle, others granulation tissue.
Theobald Smith inoculated sputum into the chest and abdomen of the following:
1. A yearling heifer, which was killed two months later and showed on the pleura near the seat of infection a mass of tubercles, one by one and a half inch in diameter, with partly caseated centres; also a nodule one-eighth of an inch on the right lung, and small tubercles attached to the diaphragm and omentum.
2. A yearling injected in the same way showed in two months on the diaphragm a mass of tubercles two inches in diameter, and a second mass one inch in diameter on the ribs near the seat of infection. Microscopical examination failed to detect bacilli, but there is no evidence that they were sought by culture or inoculation.
3. A cow injected in the chest and killed after two months showed tubercles of the lungs, pleura, and mediastinal glands, partly caseated and containing bacilli. Vascular fringes hung from the pleura.
4. A cow receiving a chest injection of sputum culture and killed in two months showed fringes and pendulous masses on the pleura, with small tubercles containing cheesy matter and a few bacilli.[[12]]
[12]. Journal of Experimental Medicine, 1898, vol. iii. p. 482.
Crookshank injected tubercular sputum into the peritoneum of a calf, which died of streptococcus infection on the forty-second day. It showed extensive tubercular deposits in the seat of injection and an abscess the size of a walnut. Nodular fleshy neoplasms in hundreds studded the mesentery, omentum, liver, spleen, and diaphragm, and small tubercles disseminated through the lungs and liver contained tubercle bacilli. Three abscesses contained streptococci.[[13]]
[13]. Transactions of the Pathological Society of London, 1891, p. 332.
The experimental inoculations of cattle with sputum by T. Smith, Kruse, and Adami showed a decided lack of potency in the bovine system, but (1) they do not show that the germ at once perishes in the system of cattle; (2) they do not prove that this germ, if returned from the ox to man, would prove less pathogenic than if carried from man to man without the intervention of the ox. (3) The observations of Bollinger, Baumgarten, and Crookshank show that under certain conditions the sputum bacillus can and does produce generalized tuberculosis in cattle. (4) Diminished pathogenesis of the germ when passed from man to cattle is no guarantee that this germ, or the slightly modified germ of casual bovine tuberculosis will prove equally mild if transferred from the bovine to the human patient.
Cases of Infection of Man from Ox. Tscherning, of Copenhagen, attended a young veterinarian who had cut his finger in dissecting a tuberculous cow. The skin wound healed in three weeks, but a subcutaneous swelling persisted, an ulcer formed, and a tuberculous mass containing bacilli was removed. No secondary tubercles formed.[[14]] A parallel case occurred to a prominent American veterinarian. The diseased tissue was excised and the bacilli identified by the bacteriologist of the university with which the patient was connected, and a permanent recovery ensued.
[14]. Nocard. Dictionnaire de Med. Veterinaire. Article, Tuberculosis.
Pfeiffer, of Weimar, attended a veterinarian who had been similarly inoculated from a tuberculous cow. The patient, aged thirty-four years, had a good constitution and no tuberculous taint. The cutaneous lesion healed, but six months later there was tuberculosis in the cicatrix; pulmonary tuberculosis followed, and the patient died of this two years later. At the necropsy were found tubercular arthritis of the wounded thumb and many vomicæ in the lungs.[[15]]
[15]. Zeitschrift für Hygiene, Band iii.
The post-mortem wart (tuberculosis verrucosa cutis) is familiar to surgeons as occurring in butchers and tanners, and there is every presumption that in many cases this is of bovine origin (Martin du Magny, Hanot, Senn, Riehl, Paltauf, Osier). Gerber testifies that in exceptional cases this extends to the lymph-glands and becomes generalized.
Dr. Stang, of Amorbach, had a five-year-old, finely developed boy patient, of healthy parents, destitute of hereditary taint. He died after a few weeks’ illness with miliary tuberculosis of the lungs and enormously enlarged tubercular mesenteric glands. The cow which supplied his milk had been killed a short time before with pulmonary tuberculosis.[[16]]
[16]. Lydtin. Veterinary Congress, Brussels, 1883.
Dr. Demme, of the Children’s Hospital, Berne, had four infants, the offspring of sound parents, with no hereditary taint of tubercle, die of intestinal and mesenteric tuberculosis, having been fed on the milk of tuberculous cows. Among 2,000 tuberculous infants treated in twenty years these were the only ones in which he could exclude the probability of hereditary and other causes.[[17]]
[17]. Nocard. Dictionnaire de Med. Veterinaire. Article, Tuberculosis.
Mr. Howe, of North Hadley, Mass., lost a son, aged twenty months, from abdominal tuberculosis, three months after he had paid a week’s visit to his uncle and had been fed the milk of the uncle’s tuberculous cow. The cow showed at death generalized tuberculosis. The child had been strong and well, as were his parents.
The four-year-old son of Colonel Beecher, of Yonkers, died March, 1894, of tubercular meningitis, and the two Alderney cows which had supplied him with milk were then proved consumptive by the tuberculin test and post-mortem examination.[[18]]
[18]. New York Sun, March 29, 1894.
The child of Dr. Brown, U. S. A., and now of Cornell University Medical School, was similarly cut off by tuberculosis, having been fed on the milk of a tuberculous cow.
Dr. C. H. Peabody had a child patient die of tubercular meningitis three months after the family cow had been killed for generalized tuberculosis. There had been previously no tuberculosis in the family (Ernst, Infectiousness of Milk).
A. H. Rose, of Littleton, Mass., gives the case of a child which was fed for three years on the milk of a tuberculous cow and died with abdominal tuberculosis (Ernst).
Gordon, of Quincy, Mass., records the case of a ten months old child of healthy parents and ancestry which had been fed on the milk of a cow with advanced tuberculosis, and which died after a few weeks with acute tuberculosis (Ernst).
Gage, of Lowell, Mass., had an infant patient of healthy parents and surroundings, but which subsisted exclusively on a cow’s milk that contained bacilli and infected Guinea pigs. The child died of tubercular meningitis. A second child fed the same milk suffered in a similar way (Ernst).
Andersen, of Seeland, reports the death from tuberculosis of a six months old child which had fed on the milk of a cow having tuberculosis of the udder. The mother developed symptoms of tuberculosis after the death of the child.[[19]]
[19]. Hatch Experiment Station, Massachusetts Agricultural College, Bulletin No. 3.
Dr. Gosse, of Geneva, Switzerland, spent his Sundays with his family on an estate in the hills, and his daughter, aged seventeen years, took great pleasure in drinking milk warm from the cows. Early in 1893 she sickened with an obscure illness, and after ten months died, revealing at the necropsy intestinal and mesenteric tuberculosis. The five cows on the estate were tested with tuberculin; four reacted and were killed; two showed tuberculous udders (Nocard).
Dr. H. M. Pond reports four cases of tuberculosis in one family, three of them fatal. The cows supplying the family with milk were tuberculous.[[20]]
[20]. Pacific Medical and Surgical Journal, 1888.
Dr. Faust, veterinarian, of Poughkeepsie, records the case of a family on Long Island that lost from tuberculosis 139 cows. A three-year-old child and two grown sons died of tuberculosis. Tuberculosis was unknown in the parents’ families.[[21]]
[21]. Report to the Board of Health.
Dr. Kelly, veterinarian, Albany, gives the following: In a family of five a son, aged nineteen years, was very fond of milk and drank it fresh from the cow, and contracted tuberculosis. Some months later the farm herd of seventeen registered Jerseys were tested with tuberculin, and thirteen reacted and showed extensive tuberculosis when killed.
Dr. Cooper, veterinarian, Paterson, N. J., furnishes this: A child, fed on the milk of a cow, contracted tabes mesenterica. Examination revealed the presence of tubercle bacilli in the milk. The milk was then fed to ten kittens, all of which became ill and emaciated, and when killed showed tuberculosis.
Such cases, in connection with the experimental inoculations, furnish more than mere circumstantial evidence. They are corroborated and strengthened by the very uniform diffusion of tuberculosis in man and stalled cattle in practically all civilized countries. Of the closer connection in individual cases one or two instances may here be added as drawn from personal observation:
1. In one case a family cow and the owner’s wife had both advanced tuberculosis. The lady consumed a good deal of the cow’s milk, but when she gave up its use she felt decidedly better.
2. The owner of a thoroughbred herd of sixty head had suffered for years from consumption, and attributed the poor condition of the animals to lack of care since he had been laid aside. Without the tuberculin test, I diagnosed tuberculosis in fifty-nine of the animals.
3. In a second thoroughbred herd there never lacked one or two cases of advanced tuberculosis, two of the family suffered, and the eldest son, who was fond of milk and vegetable food, died of pulmonary tuberculosis.
4. A dairy of common cows had seventeen out of twenty-six destroyed for tuberculosis, and the farmer’s wife, father-in-law, and two brothers-in-law had shortly before died of consumption. The wife felt ill in the close house air, and with her father occupied herself much about the cattle.
5. A veterinary professor, who was meat inspector of the city abattoir, died a few years ago of tuberculosis, which he handled so constantly in his daily duties.
Stalker and Niles report that 5 persons, 20 to 30 years of age, of healthy ancestry, died of tuberculosis within two years, on a farm where 17 tuberculous cattle were found, and others had died in previous years, (Bull. Ia. Agr. Exp. Stat., 29).
Leonhardt reports the death from tuberculosis, abdominal and meningeal, of two children, fed on the milk of a tuberculous cow, (Rep. N. H. Bd. of Health, 1892).
Sontag reports the death by tuberculosis of a six months old child of healthy parents, that had been fed the milk of a tuberculous cow, (Rep. N. H. Board of Health, 1892).
Dr. E. Pearson quotes the following:
“A well known veterinarian wounded in the hand in opening a tuberculous cow, had a tumid, intractable sore, the tissues of which when excised showed tubercle bacilli.
A veterinarian, of Chester Co., Pa., in opening a tuberculous cow, cut his knuckle, which healed tardily, remained swollen and when excised, showed typical tubercular lesions including giant cells.”
He quotes from Hartzell the cases of two men wounded in cleaning cattle cars, both of whom had resulting tubercle, arrested in one case by excision, but in the other advanced to generalized tuberculosis and death.
Bang gives the following Danish cases:
A merchant having two chlorotic daughters secured a fine cow to feed them fresh milk. The cow was killed tuberculous and was replaced by another which also showed tuberculosis, this time affecting the udder. The girls died of tuberculosis at 16 and 18 years. Two younger children fed on the milk of sound cows grew up healthy.
A healthy cow became tubercular, after having been placed in the same stall in which another had died of tuberculosis. A child fed almost exclusively on the milk of these two cows died of tuberculosis.
A peasant at Silkeborg drank freely of milk freshly drawn. He died of tuberculosis, as did also a cow, and later in the same stable, a pig.
A peasant had an 11 year old cow with generalized tuberculosis, implicating the udder. The wife of the peasant, formerly healthy, became tuberculous shortly after the udder became affected and died at 45. A daughter who, like her mother, used the milk of this cow, died consumptive in the same year. The husband who drank beer, and not milk, remained well.
A physician fed his two children on the milk of his tubercular cow, and lost both from tuberculosis. Neither parents nor grand-parents were tuberculous. (L. Pearson in Bull. 75, Tuberculosis of Cattle).
Thorne had reports from twenty-two Ohio physicians to the effect that they had traced tuberculosis in their patients to the use of the milk of tuberculous cows, and thirty-three who believed they had reason to suspect the meat and milk supply as the source of cases of consumption. (Ohio Exp. Stat. Bull. 108).
To these may be added the cutaneous forms of tuberculosis (tuberculosis verrucosa cutis), which occur on the hands of persons (butchers, tanners, coachmen, cooks, etc.), who handle infected products of animals. These have been described by Riehl and Paltauf, Senn, and a number of surgeons and dermatologists and the relation of the occupation to the seat of the disease is conclusive as to the source of the infection. It is the exact counterpart of the verrucosa necrogenica of the hands of persons working in the dissecting rooms of medical schools, and the source of infection is equally well established in both cases.
A strong argument for the appreciable influence of the bovine bacillus upon man (acting directly or indirectly through the pig) is that the relative death rate of Jews from tuberculosis is materially less than that of other races. It is constantly claimed that orthodox Jews who eat only kosher (rabbi inspected) beef and no pork, suffer least of all the population from tuberculosis. Dr. Gerster, judging by the burial returns of the United Synagogue and the English Registrar General’s returns, concludes that only about half the relative proportion of Hebrews suffer from consumption as do other races in the same country. Some remarkable facts come out in the report of the Royal Commission on tuberculosis in England. In England and Wales the disease had decreased 39.1 per cent, in thirty-five years, but this decrease has been mainly in pulmonary cases, while the abdominal forms decreased only 8.5 per cent. Sir Richard Thorne, indeed says, that in children of the first year there had been an actual encrease of 27.7 per cent. Northrup and Still, on the contrary, present statistics showing that in children the pulmonary form of tuberculosis is the most common (Brit. Med. Jour. 1898). If in the face of this there has been a very material encrease of the abdominal form, coincident with the notorious encrease of the disease in dairy cows and of the bottle-feeding of infants, may we not enquire how much of this is due to the greater prevalence of bottle-feeding and the infected cow’s milk? It is not for a moment supposed that the majority of infections in children come from the cow. The question is whether this encrease in the minority is not in measure chargeable on the cow. The impaired nutrition resulting in some instances from the use of cow’s milk cannot well be charged with a marked encrease of cases in which the mesenteric tubercles point so directly to infection through the food. If it is held that the tubercle bacilli in the milk are harmless, we wait for evidence of the real cause of such encrease and localization.
The experiments of Adami show that tubercle is directly transmissible from man to ox though usually with decreased virulence. More recently, Ravenel using the bacillus derived from the mesenteric glands of a child, injected intravenously two tuberculin-tested calves, with 5cc. each of the culture producing exalted hyperthermia, miliary tuberculosis of the lungs, tuberculosis and caseation of the bronchial and mediastinal glands, and death in 17 days. Dr. Garnault’s experiment on himself, now in progress, has already shown the great danger to a susceptible man, of the bovine bacillus.
As showing accommodation to environment, Battaillon and Ferre found that the bacillus (mammalian and avian) grown in frogs, Dubard that grown in fishes, Kráhl that grown in frogs, snakes, fishes and lizards, and Müeller that grown in the glow worm, thereafter grew at summer temperature (68° F.) and grew poorly or not at all in the bodies of mammalia.
The tubercle bacillus is primarily and essentially one, but this must not close our eyes to the fact that in different hosts and environments it takes on very different habits, so that for the time and in these surroundings, it is materially modified in its pathogenic attitude toward different races. Yet its ready variability when conditions are favorable to change, renders it desirable to destroy it in all its forms, and especially in those which approximate most closely to those that prey on man and animals.
An impartial review of the whole field warrants the conclusion that the nineteen young (and therefore comparatively insusceptible) cattle which in Koch’s hands failed to develop generalized tuberculosis after inoculation with the virulent sputum of man, and the smaller numbers that resulted in the same way under similar treatment in the hands of Th. Smith, Dinwiddie and Adami, while showing a very marked limitation in the susceptibility of the sound bovine system to weak bacilli from man, cannot disprove the many well authenticated cases of the transmission of tuberculosis from cow to man and the reverse. The greater potency of the bovine bacillus over that of man, in its action on the small rodents and pigs, utterly forbids the unproved assumption that it is on the contrary harmless to man.
If the object of the sanitarian were merely to delay a fatal result in his tuberculous patient, while he accepted the prevalence of tuberculosis as inevitable for all future time, the acknowledged lessened receptivity of the ox for the bacillus from man would mean more and would be at least worthy of a hearing, but as the extinction of a disease germ and its representative plague must ever be the first object, any movement toward the preservation in cattle of a germ which is deadly to man and much more so to cattle, must be held as subversive of the prime purpose of sanitary work. This is true even if we allow, for the sake of argument, that only a few of the bovine bacilli are capable of dangerously colonizing the human body, and that special environment is needful to allow of such successful colonization. On the other hand the limited receptivity of the ox for the bacillus from man is the greatest encouragement to active work to exterminate tuberculosis from our herds. It is impossible to adopt in man the summary measures that are so successful in the speedy stamping out of the plagues of the lower animals, so that tuberculosis in the human family can only be eradicated by slow degrees, and therefore there will long continue for our herds the danger from the human side, but just so far as the susceptibility of cattle to human tuberculosis is limited, in the same ratio are our hands strengthened in effective work for the extinction of consumption in our herds and for preserving their soundness after they have once been purified. If they were to be reinfected by the presence of any consumptive person we might well despair of success in face of a wide prevalence of tuberculosis in man, but since it is only exceptionally that cattle suffer from man, outbreaks coming from this source can the more easily be taken care of. In this view tuberculosis is approximated somewhat more closely to the other bovine plagues (lung plague, rinderpest) which can be stamped out with the greatest ease and certainty, so that as a purely economic measure the argument for the speedy extinction of tuberculosis in our herds is reinforced.