SCIENCE AND WAR 225 



medical profession, and he fought strenuously, one of 

 his disciples remarking that it is characteristic of lofty 

 minds to put passion into ideas. Swine plague, which 

 in the United States in 1879 destroyed ove'jj a mil- 

 lion hogs, and chicken cholera, also engaged his at- 

 tention. 



Cultures of chicken cholera virus kept for some 

 time became less active. A hen that chanced to be 

 inoculated with the weakened virus developed the 

 disease, but, after a time, recovered (much as patiente 

 after the old-time smallpox inoculations). It was then 

 inoculated with a fresh culture supposed sufficient 

 to cause death. It again recovered. The use of the 

 weakened inoculation had developed its resistance to 

 infection. A weakened virus recovered its strength 

 when passed through a number of sparrows, the sec- 

 ond being inoculated with virus from the first, the 

 third from the second, and so on (this species being 

 subject to the disease). Hens that had not had chicken 

 cholera could be rendered immune by a series of at- 

 tenuated inoculations gradually increasing in strength. 

 In the case of anthrax the virus could be weakened 

 by keeping it at a certain temperature, while it could 

 be strengthened by passage through a succession of 

 guinea-pigs. There are of course many instances 

 where pathogenic bacteria lose virulence in passing 

 from one animal to another, the human smallpox 

 virus, for example, producing typical cowpox in an 

 inoculated heifer. These facts help to explain why 

 certain infections have grown less virulent in the 

 course of history, and why infections of which civil- 

 ized man has become tolerant prove fatal when im- 

 parted to the primitive peoples of Australia. 



