INFECTIOUS DISEASES OF CATTLE. 439 



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

 losis, went far beyond this and maintained that " human tubercu- 

 losis 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 heredi- 

 tary 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 wliich had ap- 

 parently been demonstrated by others that it at once aroused opposi- 

 tion in the congress, followed by the adoption of dissenting resolu- 

 tions, and led to numerous investigations in various countries. 

 Koch's conclusions were based upon his failure to produce tubercu- 

 losis in cattle and other animals by inoculating them with tuberculous 

 material of human origin and his success in causing progressive and 

 fatal tuberculosis in the same kinds of animals when inoculated with 

 tuberculous 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 dis- 

 criminating 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 diag- 

 nose them. All that is necessary is to cultivate in pure culture the tubercle 

 bacilli found in the tubercular material, and to ascertain whether they belong 

 to bovine tuberculosis by inoculating cattle with them. For this purpose I 

 recommend subcutaneous injection, which yields quite specially characteristic 

 and convincing results. 



These important and comprehensive conclusions followed from a 

 comparatively few experiments upon animals, and apparently no 

 effort had been made to learn to what extent human tubercle bacilli 

 might differ in their virulence for cattle or what grades of virulence 

 there might be among bacilli of bovine origin. Vagedes had already 

 shown that bacilli were sometimes present in human lesions which 

 were as virulent as bovine bacilli, but his work was wholly ignored 

 by Koch. 



A considerable number of investigators, including Chauveau, 

 Vagedes, Ravenel, de Schweinitz, Mohler, De Jong, Delepine^ Orth, 

 Stenstrom, Fibiger and Jensen, Max Wolff, Nocard, Arloing, Belir- 

 ing. Dean and Todd, Hamilton and Young, the German Tuberculosis 

 Commission, and Theobald Smith, have found tubercle bacilli in the 



