RESPIRATION 33 



alluded to, not accurately represented, by the following 

 reactions : 



C 8 H 10 5 + Enzym + Aq = C 6 H lt O 6 



(Starch) (Diastase?) (Dextrose, etc.) 



C 6 H 12 O 6 + Yeast + Aq = 2 CO 2 + 2 C 2 H 6 O 



By what has already been said we are led to infer that 

 organisms capable of such decompositions as the above sup- 

 ply themselves by this means with kinetic energy, and can 

 flourish although little or no energy may come from other 

 sources. In fact, the yeasts are facultative anaerobic organ- 

 isms, demanding free oxygen only when inadequately sup- 

 plied with the appropriate sugar. The actual fermentation 

 is often only one of a series of processes, first made possible 

 by the inverting action of an enzym upon some not directly 

 fermentable sugar, and followed by other processes for which 

 the fermentation supplies the necessary energy. Buchner 

 and his collaborators* have demonstrated within the last 

 few years that the alcoholic fermentation by yeast is ac- 

 complished by an enzym (zymase) which splits the sugar 

 into carbon-dioxide and alcohol, releasing energy which the 

 yeast cells use. This discovery furnishes the ground for the 

 hypothesis that all respiration, not merely alcoholic fer- 

 mentation, is carried on by the living cell through the 

 agency of enzyms (see p. 19). 



The yeasts are more profitable for the commercial produc- 

 tion of alcohol, not only because of the larger amount of 

 alcohol which they will produce from a given quantity of 

 sugar, but also because they can continue their rate of pro- 

 duction in the presence of a larger amount of alcohol than 

 most organisms can survive. The species of Mucor studied 

 by Hansenf produce only from 3% to 8% of alcohol, whereas 

 the most active species of yeast can produce 14%, although 

 their activity decreases with 12%. It is obviously impossible, 

 therefore, to produce by means of yeasts alone any liquor 

 containing more than 14% of alcohol. Those wines which 



* Buchner, E. Alcoholische Gahning ohne Hefezellen. Ber. d. Deutsch. 

 Chem. Gesellsch., 1897 and years following, 

 t Loc. cit. Bd. II. p. 160. 

 3 



