RESPIRATION AND FERMENTATION 261 



are reduced. As a result of this process, they produce the higher 

 homologues of alcohol, the so-called fusel oils, while the ammonia 

 formed goes into the building of protein molecules. By intro- 

 ducing ammonia salts into the solution, the fermentation of the 

 amino acids can be markedly suppressed. 



The process of deamination may be expressed by the following 

 equation : 



RCHNH2COOH + H 2 = RCH2OH + NH 2 + C0 2 . 



In reality, the reaction does not consist in the simple addition of 

 water but, like the process of alcoholic fermentation (Art. 81), it 

 represents a combination of oxidation and reduction. The chief 

 constituents of fusel oil are amyl and isoamyl alcohol. 



Alcoholic fermentation may be produced also by certain fungi 

 of the mucor group. Developing upon sugar solutions in the 

 absence of oxygen, these fungi, instead of forming a hyphal mycel- 

 ium, form individual roundish cells, called "mucor yeast." Fer- 

 mentation by mucor does not differ in any essentials from that 

 produced by yeast, but it is more sensitive to the presence of large 

 amounts of alcohol and stops as soon as the latter has reached 2 to 3 

 per cent. True yeast, on the contrary, is very tolerant of ethyl 

 alcohol and can continue its activity till 14 to 16 per cent of it has 

 accumulated in the liquid. Because of this endurance, yeast 

 utilizes fermentation not only as a source of energy but also as a 

 means in competition with other organisms. Grape juice, for 

 instance, will readily spoil before fermentation, due to the activity 

 of various organisms, while wine, having undergone fermentation, 

 is a stable product. The accumulated alcohol prevents the devel- 

 opment of the majority of microorganisms, with the exception, 

 however, of the acetic-acid bacteria (Art. 82). To the latter, 

 alcohol is as much of a specific material of respiration as sugar is to 

 the majority of other organisms. 



A higher concentration of alcohol than 14 to 16 per cent cannot 

 be obtained by natural fermentation; hence, in order to prepare 

 stronger beverages, methods of distilling fermented liquids are 



used. 



81. Enzymes and Their Chemistry in Alcoholic Fermentation. 

 — Considered from a purely practical as well as from a theoretical 

 point of view, alcoholic fermentation is a process of extreme impor- 

 tance. It has been seen already that it may substitute normal 



