Part 69

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 When the nozzle is withdrawn from the skin, wipe it and dip it again into the strong carbolic acid to prevent any risk of infecting the tuberculin into which it is to be plunged.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. 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.

Footnote 3:

Johns Hopkins Hospital Reports, Bulletin 100.