36. SCHROEDER, E. C. 37. Experiments concerning tuberculosis. Studies in immunity from tuber- U. S. Department of Agriculture, Bureau of Animal Industry, Circular 118. Washington, 1907. 38. SCHROEDER, E. C., and COTTON, W. E. 39. 40. 41. The persistence of tubercle bacilli in the tissues of animals after injec- Experiments with milk artificially infected with tubercle bacilli. U. S. The relation of tuberculous lesions to the mode of infection. U. S. The danger from tubercle bacilli in the environment of tuberculous cattle. 42. SCHROEDER, E. C., and MOHLER, JOHN R. The tuberculin test of hogs and some methods of their infection with tuberculosis. U. S. Department of Agriculture, Bureau of Animal Industry, Bulletin SS, pp. 40, 42, 45. Washington, 1906. 43. DE SCHWEINITZ, E. A., DORSET, M., and SCHROEDER, E. C. Experiments concerning tuberculosis. The comparative virulence of human and bovine tubercle bacilli for some large animals. U. S. Department of Agriculture, Bureau of Animal Industry, Bulletin 52, part 2. Washington, 1905. 44. SMITH, THEOBALD. 45. Two varieties of the tubercle bacillus from mammals. U. S. Department of Agriculture, 12th and 13th Annual Reports, 1895-1896, pp. 149-161. Washington, 1897. A comparative study of bovine tubercle bacilli and of human bacilli from sputum. Journal of Experimental Medicine, vol. 3, No. 415, pp. 451511. New York, July-Sept., 1898. 46. VALLÉE, H. De la genèse des lésions pulmonaires dans la tuberculose. Annales de l'Institut Pasteur, tome 19, No. 10, pp. 619-624. Paris, Oct. 25, 1905, 47. VANSTEENBERGHE, P., and GRYSEZ. Sur l'origine intestinale l'anthracose pulmonaire. Annales de l'Institut THE TUBERCULIN TEST: ITS METHOD OF APPLICATION, VALUE, AND RELIABILITY. By JOHN R. MOHLER, A. M., V. M. D., Chief of the Pathological Division. THE DIAGNOSIS OF TUBERCULOSIS. The symptoms of tuberculosis in cattle are not sufficiently prominent, except in advanced stages or when superficially located, to enable one to diagnose this disease by the ordinary methods of physical examination. And the cattle may, without showing any clinical symptoms, be in such a stage of tuberculosis as to render them capable of spreading disease. Indeed, an animal may be fat and sleek, eat and milk well, have a bright, glossy coat, and be apparently in the pink of condition and still be passing tubercle bacilli through the feces or by an occasional cough, and thus endanger all the healthy cattle in the herd. Consequently such adventitious aids to diagnosis. as animal inoculation, biological test, serum agglutination reaction, and the tuberculin test are made use of in arriving at a definite opinion relative to the presence or absence of this disease. The value of all but the last of these is discounted by the technique required and their impracticability, while the tuberculin test is most satisfactory and is the best diagnostic agent known for the disease. THE ORIGIN OF THE TUBERCULIN TEST. Tuberculin was invented by Koch in 1890, and was first used experimentally in treating tuberculosis in man. In these cases it was observed that its injection was followed by a rise of temperature, which led veterinarians to apply tuberculin to suspected animals to see if a similar reaction resulted. Numerous experiments showed this to be the case, and since 1891 the use of tuberculin as a diagnostic agent for tuberculosis of cattle has been almost universally adopted in all parts of the civilized world. No one thinks of accepting tuberculin as an absolutely infallible agent, but it is immeasurably more dependable than any other method that has ever been used. THE NATURE AND APPLICATION OF TUBERCULIN. Tuberculin is the sterilized and filtered glycerin extract of cultures of tubercle bacilli. It contains the cooked products of the growth of these bacilli, but not the bacilli themselves. Consequently, when this substance is injected under the skin of an animal it is absolutely unable to produce the disease, cause abortion, or otherwise injure the animal. In case the injected animal is normal there is no more effect upon the system than would be expected from the injection of sterile water. However, if the animal is tuberculous, a decided rise of temperature will follow the use of tuberculin. In practice the tuberculin test is applied by first taking a sufficient number of temperatures, usually three, at intervals of two hours to ascertain the normal variation of temperature of the animal to be tested. The dose of tuberculin (which should always be specified on the label) is then injected hypodermically between 8 and 10 p. m. on the day of taking the preliminary temperatures." On the following day the "after" temperatures are recorded every two hours, beginning at 6 a. m. and continuing until twenty hours following the injection. Although the subcutaneous tuberculin test in bovines, when correctly applied, proves reliable in about 97 per cent of cases, there still remains a prejudice against this form of testing among farmers and dairymen, which has been difficult to overcome. It is therefore natural that any new method which may facilitate the diagnosis of tuberculosis should be accompanied by great interest. Of the various biological methods of diagnosing tuberculosis, the greatest interest has been manifested in the last few months in the cuti reaction of von Pirquet and the ophthalmo reaction of Wolff-Eisner and Calmette. As their names imply, these tests consist in the application of the tuberculin to the scarified skin and to the eye, respectively, of the animal to be tested. The very favorable results which were reported from the application of both of the above-mentioned methods excited a great deal of interest among investigators, and soon numerous results of the experiments were published, which, however, were not uniformly favorable for either of these tests. The best results were apparently obtained from the ophthalmo reaction, and if this method should prove reliable the simple method of its application would greatly aid in the early diagnosis of tuberculosis. Thus, up to the present time the ophthalmo tuberculin test has been principally applied to the human, especially infants, and while the results obtained in these tests are very encouraging, the reactions and failures were never, or only in the earliest instances, verified by post-mortem examination. It appears, therefore, desirable to test the reliability of this reaction on animals in which the reaction may be controlled by autopsies or by the known reliability of subcutaneous tuberculin test. This has been undertaken by various investigators, including the writer, and while many of the results obtained were unsatisfactory, the general findings are somewhat encouraging. The different results which were obtained might possibly be attributed to the various preparations of tuberculin which have been employed and the different strengths in which the tuberculin was applied. The varied results thus far obtained make the reliability of the ophthalmo tuberculin test for the diagnosis of tuberculosis in bovines questionable, and it will be necessary to perfect this method by further experiments. If this method of testing should prove as reliable as the subcutaneous tuberculin test, it would unquestionably greatly facilitate the eradication of tuber THE VALUE AND RELIABILITY OF THE TUBERCULIN TEST. By means of the tuberculin test an accurate diagnosis may be made in over 97 per cent of the cases tested. The relatively few failures in diagnosis are included among two classes of cattle. The first class contains those that are tuberculous but which do not react either because of the slight effect of an ordinary-sized dose of tuberculin on an advanced case of the disease with so much natural tuberculin already in the system, or on account of a previous test with tuberculin which produces a tolerance to this material lasting for about six weeks. The second class includes those that are not tuberculous but which show an elevation of temperature as a result of (a) advanced pregnancy; (b) the excitement of œstrum; (c) concurrent diseases, as inflammation of the lungs, intestines, uterus, udder, or other parts, abortion, retention of afterbirth, indigestion, etc.; (d) inclosure in a hot, stuffy stable, especially in summer, or exposure to cold drafts or rains, or (e) any change in the method of feeding, watering, or stabling of the animal during the test. Notwithstanding all these possibilities of error, the results of thousands of tests show that in less than 3 per cent of the cases tested do these failures actually occur. In the first class the chances of error are decidedly reduced by the skilled veterinarian by making careful physical examination and diagnosing these advanced cases, and by the injection of double or triple doses into all recently tested cattle, with the taking of the after temperatures beginning two hours following the injection and continuing hourly for twenty hours. In the second class errors are avoided by eliminating those cases from the test that are nearing parturition or are in heat, or show evidence of the previously mentioned diseases, or exhibit temperatures sufficiently culosis, inasmuch as farmers and dairymen probably would not object to this external method of applying the test as they do to the subcutaneous tuberculin injection. The changes in the eye resulting from a marked reaction are characteristic; intolerance to light and an increased secretion of tears are the first indications of the reaction, which may be followed by more severe symptoms, as marked congestion of the conjunctiva, a whitish film-like exudate over the bulbar conjunctiva, and a grayish yellow discharge from the eye, which, running down the face, forms crusts. The test is applied to only one eye, and in the reaction the other or control eye should remain normal. Thus far the ophthalmo and cuti tuberculin tests can not be recommended for general practice as methods of diagnosing tuberculosis of bovines, and they I will require further work and perfection before they should pass from the experimental stage and be adopted in place of the present reliable subcutaneous application. a Reports of tuberculin tests made in the fifteen years from 1893 to 1908 by Federal, State, and other officers with tuberculin prepared by the Bureau of Animal Industry show that out of 24,784 reacting cattle slaughtered, lesions of tuberculosis were found in 24,387, a percentage of 98.39. |