20 Introduction 



optical test to determine the purity of the contained atmos- 

 phere by passing a powerful ray of light through the side 

 windows. When viewed through the front, this ray was vis- 

 ible only so long as there were particles suspended in the at- 

 mosphere to reflect it. When the dust had completely 

 settled and the light ray had become invisible because of 

 the purity of the contained atmosphere, the tubes were 

 cautiously filled with urine, beef-broth, and a variety of 

 animal and vegetable broths, great care being taken that 

 in the manipulation the pipet should not disturb the dust. 

 Their contents were then boiled by submergence in a pan of 

 hot brine placed beneath the chamber, in contact with the 

 projecting ends of the tubes, and subsequently allowed to 

 remain undisturbed for days, weeks, or months. In nearly 

 every case life failed to develop in the infusions after the 

 purity of the atmosphere was established. 



II. CHEMIC CONTRIBUTIONS? FERMENTATION AND PUTREFACTION. 



As in the world of biology the generation of life was an 

 all-absorbing problem, so in the world of chemistry the 

 phenomena of fermentation and putrefaction were inex- 

 plicable so long as the nature of the ferments was not 

 understood. 



In the year 1837 Latour and Schwann succeeded in 

 demonstrating that the minute oval bodies which had been 

 observed in yeast since the time of Leeuwenhoek were 

 living organisms vegetable forms capable of growth. 



So long as yeast was looked upon as an inert substance 

 it was impossible to understand how it could impart fer- 

 mentation to other substances; but when it was shown 

 by Latour that the essential element of yeast was a growing 

 plant, the phenomenon became a perfectly natural conse- 

 quence of life. Not only the alcoholic, but also the acetic, 

 lactic, and butyric fermentations have been shown to re- 

 sult from the energy of low forms of vegetable life, chiefly 

 bacterial in nature. Prejudice, however, prevented many 

 chemists from accepting this view of the subject, and 

 Liebig strenuously adhered to his theory that fermenta- 

 tion was the result of the internal molecular movements 

 which a body in the course of decomposition communicates 

 to other matter whose elements are connected by a very 

 feeble affinity. 



Pasteur was the first to prove that fermentation is an 



