338 SCIENCE PROGRESS. 



a degree of exactitude which is quite impossible in man. In 

 the experiments of which I shall speak three classes of 

 animals were used : guinea-pigs, pigs and calves. Guinea- 

 pigs are extremely susceptible to the disease, which in them 

 never undergoes the more advanced retrogressive changes, 

 such as the extensive fibrosis and calcification which are 

 observed in men and cattle. A small dose is sufficient to 

 infect, and the disease progresses under certain circumstances 

 until all the glands and organs of the body are affected. 

 Pigs and calves vary somewhat in their resistance to the 

 disease, according to the breed. 



It is difficult in any tuberculous material obtained from 

 cattle to estimate the varying activity of the bacillus present, 

 but for several reasons which will be adduced, in the experi- 

 ments with meat and milk which will be discussed, the activity 

 of the bacillus is not a point which can be considered as of 

 great importance, inasmuch as the effect produced appeared 

 to be proportionate to the dose given. In acute specific dis- 

 eases the dose of the virus bears some relation to the severity 

 •of the disease ; this is much more so, however, in chronic 

 tuberculosis, where, owing to the slow formation of the 

 lesions, the more bacilli present the more lesions result. 

 For this and other reasons which are more fullv discussed 

 in the report of the experiments, the varying effect which 

 will be described in experiments with meat and milk, is 

 more a question of dose than of any other factor, so that 

 virulence of the virus in these experiments is practically 

 equivalent to a large dose ; non-virulence, to a small dose. 



The infective material which was used in experiments 

 was bovine tuberculous material, obtained from the organs of 

 tuberculous cattle; sputum from cases of human tuberculosis ; 

 and meat and milk from tuberculous cattle. As regards 

 meat, it may be said that the experiments showed that its 

 infectivity depended not so much on the presence of tuber- 

 culous lesions in the muscular tissue as on the contamination 

 of the meat during its removal from the carcase, so that the 

 infectivity of the meat was sometimes great and sometimes 

 slight, being dependent on the amount of smeary tuberculous 

 material which accidentally contaminated it. Milk was 



