ALCOHOLIC FERMENTS. 141 



is a single alcohol, namely, ethyl-alcohol. This alcohol, 

 together with the living yeast, will exist unaltered 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 admission of air, a 

 vigorous oxidation sets in, and the alcohol is converted into 

 carbon dioxide and water. According to later researches made 

 by the same authors, the culture-yeasts in distilleries, under 

 certain conditions, probably when the cells are in a state of 

 exhaustion, are capable of forming amyl-alcohol, acetaldehyde y 

 and furfurol; the acetaldehyde is supposed to be formed through 

 oxidation of ethyl-alcohol in the nascent state. In prolonged 

 fermentations the Saccharomycetes hydrolyse the albuminoids 

 present in the nutrient fluid to a variable extent ; they can 

 also oxidise the products to formic and valerianic acids. The 

 same authors distinguish two reactions in normal fermenta- 

 tions, namely, a sugar-hydrolysing reaction taking place in the 

 nutrient medium, and a synthetic (albuminoid) reaction taking 

 place in the interior of the organism. They regard fermen- 

 tation as an alternate hydration and dehydration. 



GENERAL REMARKS ON HANSEN'S INVESTIGATIONS. 



From the above resume it will be seen that, at the time 

 when HANSEN commenced his investigations, our knowledge of 

 the alcoholic ferments was very deficient and untrustworthy.. 

 From the foundations upwards, it was necessary to attack the 

 whole problem experimentally. For years past, HANSEN has- 

 steadily engaged in this work. 



Previous investigators had certainly travelled as far as was 

 possible along the paths which they had marked out. When 

 we compare their investigations especially those of PASTEUR 

 and REESS with those of HANSEN, we find that the latter 

 attacked the problem from new points of view and with new 

 methods. He extended his investigations on this subject far 

 and wide. His researches have not only opened up new fields 

 for scientific research, but they have also brought about a 

 reform in the fermentation industry. For these reasons it is- 



