54 SCIENCE PROGRESS 



animals upon infected material. Some of the animals so 

 treated died of generalised tuberculosis. Those which survived 

 were killed after the lapse of a certain interval of time, and 

 their organs and tissues were examined for signs of the 



disease. 



In the first series of experiments it was found that rats 

 and mice display the highest powers of resistance. Their 

 capacity for overcoming the disease is enormous. The injection 

 of small or moderate doses of the virus produced no effect at 

 all. Large doses were only sometimes fatal, and even in these 

 cases tuberculous lesions were not found on post-mortem 

 examination, death having resulted from physiological changes 

 brought about by multiplication of the bacilli in all the organs 

 and tissues. Feeding experiments equally demonstrated a high 

 degree of immunity. Twenty-six rats were fed with large 

 quantities of highly infected material for periods of from twelve 

 to twenty-three days, so that they received an enormous dose. 

 On examination, two displayed minute traces of the disease, 

 the rest were unaffected. 



Dogs come next in order of power of resistance. They are 

 very little susceptible to the bacillus of bovine tuberculosis 

 either by subcutaneous inoculation or by feeding. They are 

 more susceptible to intraperitoneal inoculation. 



In cats the results of feeding were very similar to those 

 obtained with dogs. They displayed, however, a smaller power 

 of resistance to the effects of inoculation. Kittens were more 

 susceptible than cats. 



Next comes a group consisting of goats, calves, and pigs, 

 between which no very great differences in the degrees of 

 susceptibility can be observed, all being readily infected by 

 moderate doses of the virus either by inoculation or by feeding. 

 Frequently, however, the disease was not fatal. Calves were 

 slightly less susceptible than goats, and goats less susceptible 

 than pigs. 



At the end of the scale come rabbits, monkeys, anthropoid 

 apes, and guinea-pigs. All these are extraordinarily sensitive 

 to the action of the bacilli. In the case of rabbits an attempt 

 to determine the minimum fatal dose of a culture showed that 

 so small an amount as one ten-millionth of a milligramme 

 produced generalised tuberculosis. A chimpanzee succumbed 

 to -ooi milligramme when injected subcutaneously, and two 



