HISTORY 177 



followed by the discovery by Koch of the specific bacterium of 

 the disease, led to the view that tuberculosis in all species of 

 mammals was identical. This generally accepted belief caused 

 sanitarians to look upon tuberculosis in cattle as a great men- 

 ace to public health. The result was that during the closing 

 decade of the last century, this disease in cattle was treated 

 more vigorously as a menace to the human species than as a 

 destructive disease of animals. 



In 1896, Dr. Theobald Smith pointed out that for certain 

 animals the tubercle bacteria from cattle were more virulent 

 than those from man and further that there were certain 

 morphological and cultural differences existing between them. 

 In 1S9S, he published the results of a more extended series of 

 investigations. Since that time a number of investigators 

 have arrived at the same conclusion. The fact has come to be 

 well known that certain differences exist between the bacteria 

 of tuberculosis found in the human and in the bovine species. 

 Koch's experiments reported at the tuberculosis congress in 

 London in July, iQor, give additional evidence of a difference 

 in virulence for experimental animals of the bacteria of human 

 and of bovine tuberculosis. To what extent the human 

 species becomes infected from the bovine kind cannot be 

 stated, but the accumulating evidence tends to the conclusion 

 that bovine tuberculosis is of less significance in its influence 

 upon public health than has heretofore been thought, and ol 

 more importance as a rapidly spreading and destructive dis- 

 ease among cattle. It is not proven, however, that the human 

 species is not affected with the bacteria of bovine tubercu- 

 losis. The investigations of the last five years have shown 

 that not infrequently human tubercle material will produce 

 tuberculosis in cattle. The interim reports of the Royal Com- 

 mission appointed in 1901 are important in this connection. 

 Salmon has published an important paper on the relation of 

 human and bovine tuberculosis in reply to Koch's paper of 

 1901. Concerning its transmission, the conclusion seems to be 

 warranted, that the virus of tuberculosis spreads very largely 

 among men and cattle from individual to individual of the 



