590 



VITAL ACTIONS OF THE LOWER FUNGI. 



Chemical 

 processes in 

 this fermen- 

 tation. 



mentation of carbo-hydrates by bacteria, we have not 

 uncommonly a plentiful formation of alcohol and 

 carbonic acid (see below) ; but. in this case, numerous 

 other products constantly arise, so that the amount of 

 alcohol is relatively unimportant. Hence the produc- 

 tion of alcohol and carbonic acid is not of itself 

 characteristic for the fermentation by yeast. What is 

 characteristic is the enormous and almost exclusive for- 

 mation of these bodies from definite kinds of sugar, and, 

 in contrast to the organisms which only have a similar 

 action when air is excluded, the circumstance that the 

 presence of oxygen does not hinder the formation of 

 these substances, but rather favours it. 



The mode in which glucose is broken up in the fer- 

 mentation by yeast was formerly represented by a very 

 simple chemical formula. It was believed that the 

 glucose molecule was split up into two molecules of 

 alcohol, and two molecules of carbonic acid : C 6 H 12 6 

 (glucose) = 2 C 2 H 5 , OH (tethyl-alcohol) +2 C0 2 . 

 Pasteur, however, showed that a number of other sub- 

 stances constantly appeared, even when the fermentes- 

 cible materials and the yeast were, as far as possible, 

 pure ; on an average 2 '5 to 3' 6 per cent, of the ferment- 

 ing sugar appeared in the form of glycerine (C 3 H 5 

 (OH) 3 ), and *4 to *7 per cent, in the form of succinic 

 acid (C 2 H 4 (COOH) 2 ) ; and further, there were con- 

 stantly traces of acetic acid, and often of other alcohols, 

 such as amyl-alcohol. The attempt has been made 

 to include these side products by the formula 49 

 (C 6 H 12 6 ) (glucose), +30 H 2 = 12 C 4 H 6 4 (succinic 

 acid), +72 C 3 H 8 3 (glycerine), +30 C0 2 (Pasteur), 

 or by the formula 4 C 6 H J2 6 +3 H 2 = C 4 H 6 4 

 + 6 C 3 H 8 3 +2 C0 2 +0 (Monoyer) ; but this attempt 

 has not been successful in giving a correct view of 

 the quantitative conditions. The same bye -products 

 are also found in the fermentation by the yeast forms 

 of mucor ; at any rate Fitz was able, in this case, 

 to demonstrate succinic acid with certainty. Further, 

 Brefeld found that the bye-products were the more 

 plentiful the more unfavourable were the nutrient con- 



