142 SCIENCE REMAKING THE WORLD 



caused this wholesale death. That knowledge was es 

 sential for the beginning of Pasteur's study, but was 

 merely the beginning. 



After many efforts, too many and too intensive to be 

 related in this connection, Pasteur recalled an impor- 

 tant discovery made by the Englishman, Jenner, in 

 J 798. Jenner, working in England, noted that persons 

 who milked cows which were ill with cowpox contracted 

 a disease resembling human smallpox, and that there- 

 after such persons would not contract smallpox from 

 human beings ill with that disease. Jenner devised 

 means, now improved and known to everyone, for 

 giving human beings generally the infection or vacci- 

 nation which protects against smallpox. In recalling 

 this situation, Pasteur argued that smallpox was caused 

 by a living organism; that the organism when it lived 

 in cattle did not flourish, and that this organism when 

 introduced from cattle into human beings was not vig- 

 orous enough to produce a bad case of smallpox; that the 

 case produced was bad enough, however, to leave some 

 kind of protection or immunity against an attack from 

 organisms from persons who have a vigorous case of 

 smallpox. This line of thought is most interesting 

 when we recall that we do not yet possess satisfactory 

 evidence as to just what kind of an organism causes 

 smallpox. 



Meantime Pasteur had been carrying on experiments 

 with chicken cholera. He left cultures of chicken chol- 

 era germs in his laboratory, and went away for a short 

 vacation. Upon his return he found that these old cul- 

 tures would no longer produce chicken cholera when 



