120 MICRO-ORGANISMS AND FERMENTATION. 



substance. The cause of fermentation is present in the living 

 plasma, and therefore in the interior of the cells; but it 

 operates at a moderate distance outside the cell. The 

 decomposition of sugar into alcohol and carbonic acid takes 

 place to a small extent within, but mainly outside the yeast 

 cells. This theory is thus distinctly opposed to that of 

 Pasteur, and follows on the lines of the theories propounded 

 by Stahl and Liebig. 1 



Rayman and Kruis added to our knowledge of the 

 biology of yeast-fungi by their experiments on beers which, 

 during a period of several years, had undergone fermentation 

 with absolutely pure cultures, prepared by Hansen's method. 

 These investigators found that the fermentation product 

 obtained by means of pure cultures of Saccharomycetes 

 the normal conditions of temperature, etc., obtaining in the 

 brewery being maintained is a single alcohol, namely, ethyl- 

 alcohol. This alcohol remains together with the living yeast 

 for years in the beer when the latter is preserved at a low 

 temperature and air is excluded ; when, on the other hand, a 

 yeast film is allowed to form on the surface through the admis- 

 sion of air, a vigorous oxidation sets in, and the alcohol becomes 

 converted into carbonic acid and ivater. In prolonged 

 fermentations the Saccharomycetes hydrolyse to a variable 

 extent the albuminoids present in the nutrient fluid, and 

 they can also oxidise the products to formic and valerianic 

 acids. The same authors distinguish two reactions in normal 

 fermentations, namely, a sugar-hydrolysing reaction taking 

 place in the nutrient medium, and a synthetic (albuminoid) 



1 In Bref eld's numerous mycological treatises the budding-fungi 

 occupy a somewhat prominent position ; thus this naturalist showed 

 that, many Uttiloffinea, Basidiomycetes, and other fungi can assume a 

 budding-fungus stage. This had also been previously shown by Bail, 

 Reess, Zupf, and others ; and since Brefeld did not prove whether these 

 forms exhibit the property of forming endogenous spores, which is 

 characteristic of the Saccharomycetes, nor whether they possess any 

 marked fermentative activity, his indefinite statements that they are 

 identical with the Saccharomycetes lost all weight. 



