150 THE SCIENCE OF BIOLOGY 



The confirmation of the germ-theory as a scientific fact 

 begins with Pasteur (1822-1895). Working as a chemist, 

 this great Frenchman undertook to investigate fermenta- 

 tion. He found that each kind of fermentation, had asso- 

 ciated with it a particular kind of organism. Thus the wine- 

 yeast was always present in fermenting wine, the brewer's 

 yeast in beer, the bread-yeast in dough. The organisms 

 were necessary for the process. They were also specific for 

 particular fermentations. The so-called diseases of fer- 

 mentation, which had caused such heavy losses to the wine- 

 makers and brewers of France, were caused by the presence 

 of the wrong kind of organism or by some abnormality of 

 functioning in the one normally causing the fermentation. 

 The grosser features of the process, such as liberation of gas 

 and the manner in which a little leaven could leaven the 

 whole, had long been recognized. Now, the chemical proc- 

 esses involved and their causation through the activities of 

 specific organisms yeasts and bacteria were made known. 

 The decay of organic matter, and its accompanying fer- 

 mentation, was explained as caused by microorganisms. 

 The idea was formed that diseases hi man and domesticated 

 animals, as well as in wines and beer, might likewise be 

 caused by microscopic germs. 



Following his work upon fermentation, Pasteur undertook 

 the study of a disease of silk-worms, which had caused great 

 financial loss to the silk-raisers of France. He proved that 

 there were two specific diseases among the worms, each 

 of them caused by parasitic bacteria. The problem thus 

 became one of preventing the worms from becoming in- 

 fected, with the bacteria, since there was no disease save as 

 it arose from the parasitic germs. Pasteur next turned his 

 attention to the disease known as anthrax and again dis- 

 covered a specific germ, the Anthrax bacillus. Subsequent 

 work upon rabies and other diseases led to the preparation of 

 vaccines for particular maladies. In this manner Pasteur 

 and his successors not only established the germ-theory of 



