88 



PASTEUR 



solely to the state of receptivity of the indi- 

 vidual insects, according as they were more or 

 less sensitive to the action of the parasite. Here 

 we have in embryo the theory of microbic dis- 

 eases, which was destined a few years later to 

 revolutionise the science of medicine. 



Pasteur converted himself into a cultivator of 

 silk-worms, and, after many alternations be- 

 tween success and defeat, he obtained eggs that 

 were perfectly healthy. His method was sim- 

 ple. After the moths had finished laying he 

 reduced their bodies to a pulp, and examined 

 them under a microscope, and every batch of 

 eggs that was thus shown to have come from a 

 corpusculous moth was destroyed. This opera- 

 tion, although so simple, encountered desperate 

 opposition on the part of vendors of silk-worm 

 eggs, with whose trade it interfered. It re- 

 quired all of Pasteur's energy to overcome this 

 opposition, and all his activity as well, for he 

 had to respond to all the appeals of the silk 

 producers who sought his eggs or his advice as 

 to the best methods to follow. A campaign of 



