DISEASES CAUSED BY INFECTED MILK 99 



fore, consider the relation of bovine tuberculosis to human 

 tuberculosis. 



The relation of bovine tuberculosis to human tuberculosis. 

 When Koch first discovered the tubercle bacillus, in 1882, 

 he stated that he considered tuberculosis an identical in- 

 fection both in man and cattle. This view was generally 

 accepted by scientists as well as by the public. In 1896 

 Professor Theobald Smith, then of the Bureau of Animal 

 Industry at Washington, called attention to the fact that 

 the human tubercle bacillus has certain marked charac- 

 teristics by which it may be differentiated from tubercle 

 bacilli found in lower animals. Koch developed the com- 

 parative study of the different types of tubercle bacilli and 

 in 1901, at the Congress on Tuberculosis, made his start- 

 ling announcement — that human tuberculosis and bovine 

 tuberculosis are two separate and independent diseases, 

 and that there is practically no danger of man contracting 

 tuberculosis from cattle. Koch's dictum was based upon 

 incomplete and unsatisfactory evidence. The effect of 

 Koch's statements was to stimulate work which has thrown 

 a flood of light upon the subject. Several government 

 commissions were appointed in different countries and 

 many scientists immediately took it upon themselves to 

 solve the questions raised. The results of all these ex- 

 periments, which have been going on during the past 

 ten years, are singularly imanimous in their conclusions. 

 They all show that human beings, especially children, 

 may become infected wfith tuberculosis from cattle. As 

 soon as this question was definitely settled, the next 

 problem was to determine how frequently this infec- 

 tion takes place and how serious a public health problem 

 it is. 



The German Commission on Tuberculosis examined 

 fifty-six different cultures of tubercle bacilli obtained from 

 human beings and foimd six of them of the bovine type; 

 that is, over ten per cent. In a similar series of tests con- 



