////: />' ACILLUS OF TUBERCULOSIS 309 



cially in rabbits, the bovine bacilii are more virulent than the majority 

 of those from human sources. Animals infected with the bacilli from 

 cattle, as well as those from the other domestic animals, react to the 

 tuberculin test. All these bacilli are, therefore, undoubtedly from the 

 same original stock, and at first glance we might consider it unnecessary 

 to prove that those derived from cattle were capable of causing human 

 tuberculosis. There are facts, however, which have made this inves- 

 tigation of great importance. As we investigate we find that all facts 

 tend to show that the great majority of cases of tuberculosis in human 

 adults come from human infection. The cases where fairly strong 

 proof of bovine infection has been obtained are certainly rare. 



Further, we have the undoubted fact that the long sojourn of bacteria 

 in one species of animal tends to increase the virulence of the germ 

 for that animal and to lessen it for others. 



Theobald Smith has made the interesting discovery that there is 

 a wide difference between the culture growth of the average bovine 

 bacillus and the average one from human sources; the bovine bacilli 

 when grown in glycerin broth causes the broth to become less and less 

 acid and finally feebly alkaline to phenolphthalein, while the human 

 types cause it to become only a little less acid, but never alkaline. In 

 ordinary peptone bouillon the reaction cure is the same for both. 

 The broth becomes alkaline. Tuberculin made from bovine cultures 

 is alkaline while that made from human cultures is markedly acid. 

 Both cultures act upon the glycerin, but in different ways. He had 

 previously noted that the bovine bacilli in cultures were shorter and 

 straighter, and grew less luxuriantly than those from man, and, further, 

 that the bovine bacilli were much more virulent for rabbits. He has 

 found these differences persist for long periods, and believes that the 

 simple passage through a single person in a case of human tuberculosis 

 would not be sufficient to change these characteristics. He has had a 

 chance to examine the bacilli of two cases in young children which were 

 of the bovine type, but in adults not one of some half a dozen cultures 

 showed the bovine characteristics. The proof that Theobald Smith 

 gathered, which proved the difference between the bovine and human 

 bacilli, has enabled him and others to conclusively prove that a con- 

 siderable proportion of children suffering from intestinal or mesen- 

 teric tuberculosis aie really infected with bovine bacilli. These bacilli 

 are capable of infecting cattle. 



At present then we must assume that bovine bacilli are capable of 

 infecting those who are very susceptible, such as young children. 

 Whether adults are also infected has not yet been decided. Such views 

 as Behring's, that much adult tuberculosis is due to infection in child- 

 hood with bovine bacilli which have remained latent, are probably very 

 extreme. This question is in great need of further study. At present 

 no cattle which are tuberculous should be allowed to furnish milk, or 

 at least such milk should not be used for drinking purposes without 

 being sterilized. The flesh is less harmful, as muscular tissue is seldom 

 infected. 



