422 DISEASES OF CATTLE. 



Recently there has been much discussion of the question as to 

 whether human and animal tuberculosis are identical diseases and 

 as to the possibility of the tuberculosis of animals being transmitted 

 to man or that of man being transmitted to animals. 



The fact that tubercular material from human subjects often failed 

 to produce serious disease in cattle was observed by a number of the 

 earlier investigators who experimented with such virus. It was the 

 experiments and comparative studies of Theobald Smith, however, 

 which attracted special attention to the difference in virulence shown 

 by tubercle bacilli from human and bovine sources when inoculated 

 upon cattle. Smith mentioned also certain morphological and cul- 

 tural differences in bacilli from these two sources, and in the location 

 and histology of the lesions in cattle produced by such bacilli. He did 

 not conclude, however, that bovine bacilli could not produce disease 

 in the human subject, but said: 



It seems to me that, accepting the clinical evidence on hand, bovine tuberculosis 

 may be transmitted to children when the body is overpowered by large numbers 

 cf bacilli, as in udder tuberculosis, or when certain unknown favorable conditions 

 exist. 



Koch, however, in his address at the British Congress on Tubercu- 

 losis, went far beyond this and maintained that "human tuberculosis 

 differs from bovine and can not be transmitted to cattle." As to the 

 susceptibility of man to bovine tuberculosis, he said it was not yet 

 absolutely decided, but one was "nevertheless already at liberty to 

 say that, if such a susceptibility really exists, the infection of human 

 beings is but a very rare occurrence." He emphasized this view in 

 the following language : 



I 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 I therefore do not deem it advisable to take any measures 

 against it. 



This conclusion was so radically different from the views of most 

 experimenters and so out of harmony with facts which had apparently 

 been demonstrated by others that it at once aroused opposition in the 

 congress, followed by the adoption of dissenting resolutions, and led 

 to numerous investigations in various countries. Koch's conclusions 

 were based upon his failure to produce tuberculosis in cattle and other 

 animals by inoculating them with tubercular material of human origin, 

 .and his success in causing progressive and fatal tuberculosis in the 

 same kinds of animals when inoculated with tubercular material of 

 bovine origin. With such positiveness did he hold to the constant 

 and specific difference between the human and bovine bacillus that he 

 promulgated an experimental method of discriminating between them. 

 Speaking of the etiology of intestinal tuberculosis in man, he said: 



Hitherto nobody could decide with certainty in such a case whether the tuber- 

 culosis of the intestine was of human or of animal origin. Now we can dia°nose 



