soundness of these generalizations had been established by a thorough course of experimentation. When Koch said in the British Congress on Tuberculosis that he should estimate the extent of infection by the milk and flesh of tubercular cattle and the butter made of their milk as hardly greater than that of hereditary transmission, and that he therefore did not deem it advisable to take any measures against it, he went far beyond what was justified by any experiments or observations which he reported, and he did an immense amount of harm which will be manifested for years to come to those who endeavor to guard the human race from the dangers of animal tuberculosis. The researches to which your committee has alluded make these dangers more definite and certain than they have appeared before, and sanitarians should therefore most earnestly endeavor to counteract the erroneous and harmful impression which was made by Koch's address at London and his subsequent address at the International Conference on Tuberculosis at Berlin. Now that the conclusions of the London address are shown to be incorrect and based on insufficient experimentation, it is well that some attention should be given to the Berlin address, in which certain rules were laid down for testing all clinical evidence before it can be accepted as indicating the transmission of tuberculosis from animals to man. While your committee agrees that it is advisable to scrutinize clinical evidence as carefully as possible before it is accepted as influencing the decision of such an important question, consistency demands that we should accept clinical evidence bearing upon the transmission of bovine tuberculosis to man on the same terms that we accept evidence bearing upon the transmission of tuberculosis from man to man. For instance, Koch said in his London address, "So the only main source of the infection of tuberculosis is the sputum of consumptive patients." How does he know this? Has he any evidence to support this conclusion which will stand the requirements which he has laid down for those who oppose his views with reference to the transmission of animal tuberculosis to man? If so, this evidence has not yet been presented. Your committee believes that the principal source of tuberculosis in man is infection from other tuberculous human subjects, but it also believes that a considerable proportion of the cases of tuberculosis in man is due to infection from animal sources; and in weighing the evidence by which we are to fix more rigorously the relation which these two sources of infection bear to each other it is logical that we should apply the same rules of evidence in each case. The rules which Koch formulated for testing the evidence as to bovine infection are given below, with such brief comments as your committee feels they deserve: (1) Certain proof of tubercle, and, where possible, the primary focus must be supplied. To this condition no objection is raised, but it should be remarked that the location of the primary focus, which is made so much of, is of little value in determining the origin of the infection. It has been clearly shown by various investigators, whose work has been referred to in the preceding reports of this committee, that tubercle bacilli may pass through the walls of the intestine without producing any lesion at the point of entrance, and that their first point of lodgment and multiplication may be the mesenteric glands, the liver, spleen, or even the lungs. On the other hand, Koch has told us that the location of the primary lesion in the intestine is of no significance, because human as well as animal bacilli may be swallowed and may be the cause of such lesions. It is therefore not at all apparent that this is an essential point. (2) Other sources of infection must be excluded with certainty. This condition appears to exclude all clinical evidence bearing upon the source of tubercular infection. How is it possible to prove that any given individual has not been exposed to the bacilli of human tuberculosis? And, for the same reason, how is it possible to prove that any given individual has not been exposed to the bacilli of animal tuberculosis? It may be said that this consumptive person had habitually been in a room with another consumptive patient and was infected from that patient; but how can you prove that this person never ate any tuberculous meat, never partook of any tuberculous milk, never ate any butter containing the tubercle bacillus, never had an opportunity to be indirectly infected from the hands of cooks or from table utensils which had been in contact with tuberculous meat, milk, or butter, and was never exposed to the infection scattered in so many ways by tuberculous animals? It is impossible to exclude with certainty all these sources of infection, and if we apply the condition under discussion to the evidence upon which Koch based the assertion that the main source of the infection of man is the sputum of consumptive patients we should find no part of it that would stand the test. Now, is it logical to accept clinical evidence as to the transmission of tuberculosis from man to man by one set of rules and to require an entirely different set of rules when considering evidence as to the transmission of the same disease from animals to man? Your committee is of the opinion that clinical evidence should be regarded as valuable in confirming experimental researches, or in indicating the probable facts where experimentation has been insufficient or is impossible, but that it is too much to expect that clinical evidence will be forthcoming as to the transmission of tuberculosis which will exclude all possible sources of error. (3) In each case of alleged infection from milk affected with bovine. tuberculosis the condition of the rest of the people who have taken the same milk should be borne in mind. These fellow-consumers form to a certain extent a control experiment, and if of the numerous people who have drunk the suspected milk only a single one sickens, this weighs decidedly against the belief that this one person was infected by the common food. This condition also is regarded by your committee as illogical and impossible of general application without discarding all clinical evidence upon this question. If we apply it to the alleged cases of sputum infection, we find it is seldom, indeed, that the disease in more than one person can be traced with any probability to the same tuberculous patient, although scores of persons may have been exposed to that patient. Most people who escape tuberculosis have nevertheless been exposed many times to tuberculous patients, but this is not sufficient reason for concluding that others have not contracted the discase by similar exposure. Tuberculosis is a disease which is communicated with such difficulty among people under ordinary conditions of life, by exposure either to diseased persons or to tuberculous food, develops so slowly, and varies so much in the period which elapses before symptoms are observed, that it is only very rarely that groups of cases are observed which even appear to have originated from the same source. And yet how erroneous it would be to exclude clinical evidence suggesting contagion because only one of those exposed to a certain consumptive patient had contracted the malady. (4) The source of the milk should be attended to. Since in recent years it has become more and more evident that milk containing tubercle bacilli is yielded only by such cows as suffer from tuberculosis of the udders, the general statement that some one has drunk milk from a cow suffering from tuberculosis no longer suffices to prove to us that bovine tuberculosis bacilli have really reached his digestive It must be from a cow with tuberculosis of the udder, and therefore a statement on this subject should not be wanting in a report on milk infection if it is said to be complete. Your committee finds this statement of fact to be incorrect, since the tendency of recent investigations by competent persons is to make it more and more evident that cows with tuberculosis may yield milk containing tubercle bacilli when the udders present no signs of the disease. The argument is therefore antiquated. Of the many experiments that have been made to determine the proportion of tuberculous cows which yield infectious milk, the average results are about 15 per cent, while the cases of tuberculosis of the udder are about 2 per cent. In recent investigations made by Mohler, of the Bureau of Animal Industry, with 56 reacting cows, it was found that 12 of these, or 21.4 per cent, at one time or another during the experiment gave milk which contained virulent tubercle bacilli. Undoubtedly cows with tuberculosis of the udder yield milk containing a larger number of tuberculosis bacilli than do those in which the udder remains unafH. Doc. 743, 58-2-7 fected, and are therefore more dangerous, but it has been clearly shown that other tuberculous cows may yield virulent milk. to man. So much for the conditions laid down by Koch for testing clinical evidence bearing upon the transmission of tuberculosis from animals The effort to rule out all such evidence by applying impossible tests does not meet with our approval, but fortunately clinical evidence is no longer necessary for deciding the question. The subcutaneous injection of cattle with pure cultures of the tuberculosis bacillus from human sources, which, according to Koch, "yields quite specially characteristic and convincing results," has proved, in the hands of the German commission no less than in those of independent investigators, that bovine tuberculosis is communicable to man. It will require much work to decide with even approximate accuracy the proportion of human tuberculosis caused by animal infection; but the fact that 25 per cent of the cases in children investigated by the Geran commission, and 50 per cent of similar cases investigated by de Schweinitz, showed by this test that they were caused by animal infection is sufficient to convince us that measures should be taken and enforced at once to guard against infection from this source. In concluding, your committee desires to express its appreciation of the prompt, intelligent, and indefatigable work of those scientific investigators who took up this question immediately after it was brought to the front at London, and in the comparatively short period of about two years have furnished the material for definitely settling it, so far as the principal contention is concerned. (1) Коси, ROBERT. BIBLIOGRAPHY. Address on the combating of tuberculosis in the light of experience gained in the combating of other infectious diseases. Trans. Brit. cong. on tuberculosis for prevention of consumption, London, July 22–26, 1901, v. 1, pp. 23-35. 1902. (2) SMITH, THEOBALD. A comparative study of bovine tubercle bacilli and of human bacilli from sputum. Journ. Exper. Med., v. 3, p. 506. 1898. (3) KOSSEL, H. Mittheilungen über Versuche an Rindern mit Tuberkelbacillen verschiedener Herkunft. Berl. klin. Woch., 40. J., No. 29, 20. Juli, pp. 653-657. 1903. (4) DE SCHWEINITZ, E. A., and M. DORSET, Experiments in the virulence of tuberculosis bacilli. Bul. No. 52, Bureau of Animal Industry. (5) Report not yet published. A CHEMICAL EXAMINATION OF VARIOUS TUBERCLE BACILLI. By E. A. DE SCHWEINITZ, PH. D., M. D., and M. DORSET, M. D., 1 upon The preliminary work of Hammerschlag 1a the substances contained in the bodies of tubercle bacilli which could be extracted with ether and alcohol, and the probable composition of the extracts so obtained, offered considerable material for speculation. Nothing further was done in this line, however, until we reported investigations which we had made confirming the work of Hammerschlag indicating the presence of a large percentage of ether and alcohol soluble material in tubercle bacilli. By a chemical examination of these extracts we were also able to determine the presence of volatile fatty acids, together with other acids of the fatty series of which only the melting points were determined. More recently Klebs reported the presence of considerable fatty material in tubercle bacilli. Weyl found that the fatty extract of tubercle bacilli was possessed of the same "acid fast" property that is exhibited by the bacilli themselves. Ruppel claims to have isolated three different fatty substances from the tubercle bacilli. Several years after we had published our preliminary work Aronson reported a chemical examination which he had made of the bodies of tubercle bacilli. In this article he claims that a very large proportion of the ether and alcohol soluble material consists of free fatty acids. This statement, however, is not entirely confirmed by our own work. Levene has reported analyses of human tubercle bacilli which were grown upon the ordinary glycerine bouillon and upon a similar medium containing mannite. By these analyses he found a considerable variation in both the percentage of extractive material and in the percentage of ash obtained after burning. In a recent article Kresling reviews the work of various authors relating to the chemical constitution of tubercle bacilli of human origin, and also reports the results of his own analyses. The order in which the several solvents were used was varied considerably. The percentage obtained, however, was in all cases approximately the same. The bacilli had been collected during a number of years and had been cultivated upon the ordinary glycerine bouillon containing sodium chloride and peptone. Kresling found that the chloroform extract, chloroform being the first extractive used, contained about 14 per cent of free fatty acid. a The numbers refer to the bibliography at the end of the article. |