262 TEXTBOOK OF PLANT PHYSIOLOGY 



respiration. According to a well-known statement made by Pas- 

 teur, who first demonstrated the existence of anaerobic organisms, 

 it is "life without oxygen." 1 At the same time, its chemistry is 

 simpler than that of splitting of the respiratory material in aerobic 

 respiration accompanied by oxidation. The study of the chem- 

 istry of alcoholic respiration has attracted the attention of investi- 

 gators, for a long time, but only recently has a successful solution 

 of this question been found. 



Previously, fermentation was considered to be the result of 

 general metabolism within the yeast cell. The organism was 

 supposed to absorb sugar and after a series of transformations of 

 the sugar molecule, to eliminate alcohol and carbon dioxide. A 

 number of investigations have shown, however, that fermentation 

 and the vital activity of yeast are two different processes. Thus, 

 if yeast is supplied with pure sugar in the absence of nitrogen and 

 mineral substances, it will ferment the sugar, but will not multiply. 

 On the other hand, fermentation in the presence of oxygen pro- 

 ceeds somewhat more slowly, but oxygen exerts on the multipli- 

 cation of yeast cells a pronounced favorable influence. In order 

 to obtain more alcohol it is expedient, therefore, to limit the access 

 of oxygen, while for obtaining the largest possible quantity of 

 yeast, as in the manufacture of pressed yeast, it is more profitable 

 to give the liquid abundant air. 



The experiments by Buchner have supplied conclusive evidence 

 that fermentation may take place apart from the manifestation of 

 vital activities of the yeast cell. Having ground up yeast with 

 sand and diatomaceous earth, he subjected the mass under a 

 hydraulic press to 300 to 400 atmospheres pressure and succeeded 

 in obtaining a transparent juice which contained no living cells, but 

 nevertheless caused sugar to ferment. The active substance in this 

 juice could be precipitated by acetone or alcohol, and redissolved 

 without losing its capacity to produce fermentation. This sub- 

 stance is classified as an enzyme and is called "zymase." 



The discovery of zymase created an epoch in the study of fer- 

 mentation and enzymatic reactions in general. For the first time 

 an enzyme was obtained which produced not merely a simple 

 hydrolysis but a very complex process till then considered to be the 

 result of a complicated metabolism. In due time there were dis- 

 covered simpler methods of obtaining zymase, for example, by 



1 This of course does not mean the absolute absence of oxygen. 



