had already been reached by some writers in this country that mankind was not susceptible to the form of tuberculosis which affects cattle. Now that this conclusion has been accepted and promulgated by Koch in his address at the British Congress on Tuberculosis, and has been received so seriously by people generally as well as by the medical profession, it is deemed desirable to recapitulate what was said at that time and to add such further evidence and arguments as are available. In this discussion we should never lose sight of the fact that, even if Koch's position is correct as to the insusceptibility of mankind to bovine tuberculosis-a conclusion which your committee believes is unwarranted by the evidence-and if it is admitted that it is unnecessary to adopt measures against the bovine disease in the fight against human tuberculosis, it does not follow, by any means, that the products of these diseased animals are harmless and should be allowed to go into consumption. Nevertheless, Koch's conclusion is being used already as an argument and excuse for the sale of tuberculous meat and milk. This discussion as to the communicability of bovine tuberculosis should not be allowed to obscure the general question of the importance of condemning meat and milk of diseased animals, whether the disease is or is not a specific one which may be communicated to the consumer of these products. There is no argument to justify the sale of milk secreted from tuberculous udders, reeking with pus the microorganisms which it contains, changed in its chemical composition, and unsavory to every civilized person. The question of the desirability of measures against bovine tuberculosis as a part of the campaign against human tuberculosis is a thing by itself and entirely distinct from the desirability of such measures from an economic and general public health standpoint.

and

Whenever this question is discussed in medical meetings or medical journals the general excuse for a toleration of the present condition of affairs is that the danger from bovine tuberculosis has been greatly exaggerated. Quite likely it has been exaggerated by some individuals, but it has just as certainly been underestimated by others. What has been the effect of the discussions heretofore held? Have the public been too much alarmed? Have sanitarians gone to too great extremes? Have we anywhere a too rigid meat inspection or a too careful supervision of the milk supply? If so, your committee is not aware of the fact. And, until this occurs, the repetition of the statement that the danger from bovine tuberculosis has been exaggerated appears to be entirely superfluous and useless.

Koch in his recent paper makes two radical assumptions: First, human tuberculosis differs from bovine tuberculosis and can not be communicated to cattle; second, mankind is nearly, if not absolutely, insusceptible to bovine tuberculosis. It is incumbent upon us to examine the evidence upon which these propositions rest, for if they

can be demonstrated the fact would be welcomed by every sanitarian, not because it would no longer be necessary, for economic and public health reasons, to control bovine tuberculosis, but because it would prove that some dangers which we have hitherto feared do not exist, and it would simplify the measures needed in the warfare against human tuberculosis. We should not allow ourselves, therefore, to be biased by preconceived opinions, but should honestly and conscientiously weigh all evidence that is presented.

Neither of these propositions is original with Koch, but this is probably the first time that a scientific man of such standing and authority has ventured to adopt them. Sidney Martin, in his experiments for the British royal tuberculosis commission of 1895, showed that sputum from man was far less virulent for animals than was bovine tubercular material. Theobald Smith, Frothingham, and Dinwiddie have repeated these experiments with cattle and other animals and incontestably demonstrated this conclusion. It does not appear to be entirely correct, however, to say that human tuberculosis is not communicable to cattle. It would be more accurate to say that in the experiments referred to human tuberculosis was only communicated with difficulty to cattle, and when it was communicated it remained localized and did not cause a fatal disease.

Of 6 calves to which sputum was fed by Martin, 2 showed no lesions, 1 had 53, 1 had 63, and 2 had 13 tubercular nodules, respectively, in the intestines. In one of these animals the mesenteric Smith also produced small lesions in some

glands were also affected.

of the animals with which he experimented. The failure to cause fatal disease in cattle with sputum bacilli appears to be due to lack of virulence, or, we might say, to low pathogenic power rather than to any essential difference in bacilli from human and bovine sources. This is shown by the fact that human bacilli were less active, not only when inoculated upon cattle, but also when inoculated upon other species of animals.

The experiments of Chauveau, which were made prior to those mentioned above, are more conclusive and can not be ignored in discussing this question. In one series of experiments he infected 2 heifers and a bull, all under 1 year old, with emulsions made from tuberculous human lungs. These infections were by ingestion, but two doses being given to each animal. One of the heifers, killed fifty-seven days after infection, had more than 200 tubercles of different sizes in the small intestines. There were also tubercles in the cecum, colon, abomasum liver, and peritoneum. The autopsy on the second heifer occurred fifty-nine days after infection. In this case the abdominal lesions were insignificant, consisting of two or three follicular hypertrophies in the jejunum and a few small tubercular mesenteric glands. The right submaxillary gland and the two retropharyngeal glands were enlarged and

affected with typical tubercular infiltration. The lungs showed not less than twelve tuberculous centers, most of them the size of a walnut, and near these masses were points where tubercular infiltration was beginning. All the bronchial and mediastinal glands were enlarged, tuberculous, and infiltrated with gray and yellow matter. The bull was destroyed on the thirty-fourth day. There was a plain tuberculous eruption in the small intestine, some portions of the mucous membrane, particularly on the Peyer's patches, being covered with confluent tubercles. In the left lung there was a single tuberculous nodule of considerable size, and some lobules presented a gelatinous appearance and consistency. There were aggregations of small tubercles in the larynx and upper part of the trachea, some of which were already ulcerated. There were also tubercular granulations in the bronchi. At the time these animals were infected, three similar animals were infected in like manner with bovine material, and three others were held as checks. The latter were found free from tuberculosis. At the autopsy it was impossible to distinguish any difference between the animals infected with human and those with bovine materia'. All were affected, and with all the tuberculous lesions had the same characters.

Chauveau, also, made comparative experiments by intravenous injection and subcutaneous inoculation; from all of these he concluded that the human tuberculous virus acts on the bovine species exactly like the tubercular virus which comes from the bovine species itself '

1

That the diseases are not absolutely distinct is indicated by the fact that tuberculin made from human bacilli causes a reaction in cattle affected with bovine tuberculosis. The Bureau of Animal Industry has distributed hundreds of thousands of doses of tuberculin made from human bacilli, and this tuberculin has been used by State authorities in various parts of the United States for diagnosing the disease in cattle, and has been found extremely reliable and satisfactory for this purpose. This fact would clearly indicate that if there is a difference between bacilli from human and bovine sources and your committee is inclined provisionally to admit such a difference-it consists in minor biological variations and not in the germs being specifically distinct.

In discussing the susceptibility of man to bovine tuberculosis, it appears to your committee that Koch has simply begged the question. Even if we admit that human tuberculosis is not readily communicable to cattle, the conclusion that bovine and human tuberculosis are entirely different and not intercommunicable between these species does not necessarily follow. Another possible conclusion, and one more in harmony with what is known of comparative pathology, is that the

Proceedings of the Congress for the Study of Human and Animal Tuberculosis, second session, Paris, 1891, p. 51.

bovine bacillus, being proved more virulent for all animals upon which it has been tried, is also more virulent for man.

As pointed out in this committee's report of last year, there is no contagion which affects so many and such widely separated species of animals as does the bovine bacillus and which is not at the same time pathogenic for man. Bovine tuberculosis is communicable to horses, cattle, sheep, swine, dogs, cats, guinea pigs, and rabbits. This is a very extensive range of pathogenic power. What other pathogenic germ is there which is virulent for so many and such widely separated species and which is not virulent also for man?

As examples of diseases which affect many species of animals, we have anthrax, rabies, glanders, malignant edema, and tetanus, to ali of which mankind is susceptible. As examples of diseases which affect a fewer number of species, we have epizootic aphtha, which principally affects cattle and swine, and which is communicable to man; we have vaccinia, or cowpox, which affects horses and cattle and which is communicable to man; we have rinderpest, which affects only ruminants and which is not communicable to man; we have pleuropneumonia and Texas fever, which affect cattle and are not communicable to man; and we have sheep pox, which affects sheep only, and hog cholera affecting swine only, which are not communicable to man. The rule appears to be that the larger the number of animal species susceptible the more likely is a contagion to affect man. Surely a germ which is pathogenic for so many species of animals as is the bovine tubercle bacillus, should be considered as dangerous to man until positive evidence has proved its innocence.

We are not without parallel cases in comparative pathology, which should be considered in deciding such an important question. One of these is found in rabies. When the contagion of this disease is inoculated into monkeys and passed from one animal of this species to another for a few times, the virus, as is well known, becomes so lacking in pathogenic power that it no longer produces rabies in dogs when inoculated in the usual manner. It must be apparent to all how wrong it would be to conclude that because rabies of monkeys is not communicable to the dog, conversely the rabies of the dog is not communicable to monkeys; yet this appears to be exactly the kind of assumption which Koch has made in regard to the bovine tubercle bacillus.

Another parallel case is found in variola. The variola of man, commonly called smallpox, is conveyed to cattle with much difficulty. Like human tuberculosis, it produces, when inoculated in these animals, only insignificant results when compared with the disease in man, with no tendency to generalization or to the production of fatal results, but, on the other hand, the tendency is to retrogression and healing. Nevertheless, the bovine variola, known as vaccinia, or

cowpox, is easily inoculated upon man, develops to the same extent as in cattle, produces characteristic lesions, runs its regular course, and may be transferred from man to man an indefinite number of times, as has been shown in the practice of vaccination. If cowpox had never been experimentally tested upon man, and we had only the results of experiments in inoculating smallpox upon cattle, we should have the same reason for concluding that vaccinia is not communicable to man that has been cited in the case of tuberculosis.

In

Koch alludes to two kinds of evidence available for deciding this question: First, the demonstration of cases of primary intestinal infection in man; secondly, the inoculation of cattle with bacilli found in cases of human tuberculosis. It appears to your committee that his treatment of this question is very narrow and unsatisfactory. deciding as to the susceptibility of man the evidence now available may be classified under four heads: (1) Accidental inoculations with bovine bacilli; (2) Clinical evidence of individuals infected by use of milk; (3) Statistics of abdominal tuberculosis; (4) Results of postmortem examinations. We shall discuss the subject under these four heads.

ACCIDENTAL INOCULATIONS OF MAN WITH BOVINE BACILLI.

The first and most important line of evidence is that obtained from accidental inoculations of man with bovine bacilli. Ravenel1 has put on record three cases of veterinarians in the State of Pennsylvania who were accidentally inoculated with bovine tuberculosis in making postmortem examinations. Case 1 was accidentally wounded in the knuckle of his forefinger. The wound healed badly and a nodule soon formed which showed a decided tendency to ulcerate. After some weeks he had the nodule removed, and a section of the excised portion was found. to contain a large giant cell, but tubercle bacilli were not satisfactorily demonstrated in the preparation. The nodule recurred after excision and was finally cured by treatment in the hot-air apparatus. Case 2 was Ravenel's assistant, who scratched his knuckle on the broken end of a rib in performing a postmortem on a goat which had succumbed to an experimental inoculation with a culture of bovine tubercle bacillus. The wound healed promptly, but about three weeks after became reddened, swollen, and sensitive. It grew worse and was finally excised with a margin of healthy skin. Two guinea pigs were inoculated subcutaneously with a portion of this nodule and both of these developed a generalized tuberculosis. Case 3, a well-known veterinarian of Philadelphia, wounded the knuckle of his forefinger in making an autopsy on a tuberculous cow. Between three and four

Three Cases of Tuberculosis of the Skin due to Inoculation with the Bovine Tubercle Bacillus. Mazyck P. Ravenel, Philadelphia Medical Journal, July 21, 1900.