230 MICRO-ORGANISMS AND FERMENTATION. 



appearance of sugar, spirit of wine, carbon dioxide, and acetic 

 acid were formed. He explained the process as the splitting 

 up of an oxide into substances both poorer and richer in 

 oxygen. As the yeast played no part in determining the 

 quantitative ratio of these he did not concern himself further 

 with it. 



At the beginning of the nineteenth century Gay-Lussac 

 published the well-known equation of fermentation, which 

 still holds good, according to which a molecule of grape sugar *" 

 was decomposed into two molecules of carbon dioxide and two- 

 molecules of alcohol. The basis was thus given for a definition 

 of fermentation viz., a breaking down of complex bodies 

 into bodies of simpler construction. 



The question now arose in what way this transformation 

 was brought about ; what was the true cause of the decom- 

 position of the liquid ? 



In the literature of the seventeenth, and still more in that 

 of the eighteenth century, allusions are made to a " ferment " 

 (Willis, Stahl) which was declared to be " a body existing in 

 a state of internal motion which transfers its motion to other 

 bodies present in the liquid, whereby the coupling of the 

 compounds present is torn apart. The fragmentary particles 

 are, however, through constant friction, attenuated and trans- 

 formed into a new and more stable compound." These indica- 

 tions, however, remained unheeded. In 1810, Gay-Lussac,. 

 encouraged by the brilliant chemical discoveries of Lavoisier, 

 undertook experiments to elucidate the process of fermentation, 

 starting from Appert's method of preparation, which consisted 

 essentially of preventing organic matter from undergoing 

 fermentation by boiling it, and immediately afterwards 

 sealing it tightly in vessels so that no air could penetrate to 

 it. This process was, however, no new one, for as early as 

 1782 the Swedish scientist, Scheele, proved that acetic acid 

 can be preserved unaltered after subjection to heat. 



Gay-Lussac examined the air contained in such hermeti- 

 cally sealed vessels, and found that it contained no oxygen. 

 In his Zeitdlter des Sauerstoffs, this observation led to the 

 view that oxygen itself was the true cause of the process of 

 * Not cane sugar, as Gay-Lussac believed. 



