CHAPTER IV 



BACTERIA AND FERMENTATION 



IT was Pasteur who in 1857 ^^st propounded the true cause 

 and process of fermentation. The breaking down of 

 sugar into alcohol and carbonic acid gas had been known, 

 of course, for a long period. Since the time of Spallanzani 

 (1776) the putrefactive changes in liquids and organic matter 

 had been prevented by boiling and subsequently sealing the 

 flask or vessel containing the fluid. Moreover, this success- 

 ful preventive practice had been in some measure correctly 

 interpreted as due to the exclusion of the atmosphere, but 

 wrongly credited to the exclusion of the oxygen of the air. 

 It was not until the beginning of the present century that 

 authorities modified their view and declared in favour of 

 yeast cells as the agents in the production of fermentation. 

 That this process was due to oxygen per se was disproved 

 by Schwann, who showed that so long as the oxygen ad- 

 mitted to the flask of fermentative fluid was sterilised no 

 fermentation occurred. It was thus obvious that it was not 

 the atmosphere or the oxygen of the atmosphere, but some 

 fermenting agent borne into the flask by the admission of 

 unsterilised air. It was but a step to further establish this 

 hypothesis by adding unsterilised air plus some antiseptic 

 substance which would destroy the fermenting agent. 

 Arsenic was found by Schwann to have this germicidal 

 faculty. Hence Schwann supported Latour's theory that 

 fermentation was due to something borne in by the air, and 



III 



