FERMENTATION 109 



' gas ' van Helmont did not mean an air or vapour, still 

 less did he mean an illuminant. He understood by 

 this term carbon dioxide, and he points out that when 

 sugary solutions ferment, this gas is given off. 



About 1700 Stahl, returning to a view put forward 

 by Willis in 1659, propounded the first physical view 

 of fermentation. The ferment was to their minds a 

 body with a certain internal motion which it trans- 

 mitted to the fermentable matter. Stahl extended this 

 view to the processes of putrefaction and decay. One 

 hundred years later Gay-Lussac taught that the fer- 

 mentation was set up by the presence of oxygen. The 

 yeast-cells had been seen and described by Leeuwen- 

 hoek as far back as 1675, but they seem to have 

 attracted little attention ; and it was not until Schwann 

 published his researches, the earliest of which is dated 

 1837, and until Cagniard de Latour, about the same 

 date, put forward his vitalistic theory — the theory 

 which attributes fermentation to the action of living 

 organisms — that they were recognized as playing an 

 important part in fermentations. Even then they 

 were not allowed to hold the field. Liebig brought 

 the weight of his great authority to oppose the 

 vitalistic theory. In his view the ferment was an 

 unstable organic compound easily decomposed, which 

 in decomposing shook apart the molecules of the 

 fermenting material. This theory and that of Ber- 

 zelius, who regarded fermentation as a contact action 

 due to some ' catalytic ' force, divided between them 

 the allegiance of the chemical world, when, in the 

 year 1854, Pasteur was nominated Professor and Dean 

 of the new Faculty of Science at Lille. 



Here, in the centre of the beetroot industry, 

 Pasteur had ample opportunity to study the pre- 

 paration of alcohol. The father of one of his students 

 owned a distillery, and suffered occasional loss from 

 the fermentations turning sour owing to the formation 



