INTIiODUCTION ix 



how the atmosphere produces decomposition of organic sub- 

 stances, we find that a flood of light has been thrown upon 

 this most important subject by the philosophic researches of 

 M. Pasteur, who has demonstrated by thoroughly convincing 

 evidence that it is not to its oxygen or to any of its gaseous 

 constituents that the air owes this property, but to minute 

 particles suspended in it, which are the germs of various low 

 forms of life, long since revealed by the microscope, and 

 regarded as merely accidental concomitants of putrescence, but 

 now shown by Pasteur to be its essential cause, resolving the 

 complex organic compounds into substances of simpler chemical 

 constitution, just as the yeast plant converts sugar into alcohol 

 and carbonic acid.'^ From these beginnings modern surgery 

 took its rise, and the whole subject of wound infection, not 

 only in relation to surgical diseases, but to child-bed fever, 

 forms now one of the most brilliant chapters in the history of 

 Preventive Medicine. 



II. 



Pasteur was early impressed with the analogies between 

 fermentation and putrefaction and the infectious diseases, and 

 in 1863 he assured the French Emperor that his ambition was 

 **to arrive at the knowledge of the causes of putrid and con- 

 tagious diseases." After a study upon the diseases of wines, 

 which has had most important practical bearings, an oppor- 

 tunity came of the very first importance, which not only 

 changed the whole course of his career, but had great influencf 

 in the development of medical science. A disease of the silk- 

 worm had, for some years, ruined one of the most important 

 industries of France, and in 1865 the Government asked 

 Pasteur to give up the laboratory work and teaching, and to 

 devote his whole energies to the task of investigating it. The 

 story of the brilliant success which followed years of application 

 to the problem will be read with deep interest by every student 

 of science. It was the first of his victories in the application 

 «>f the experimental methods of a trained chemist to the 



