264 TEXTBOOK OF PLANT PHYSIOLOGY 



instance, consider lactic acid as one of the intermediate products. 

 These various theories will not be discussed in detail here, since 

 none of them give a satisfactory explanation of the internal chem- 

 ical processes of fermentation and none can be considered as finally 

 proved. Certain fundamental ideas common to all of the theories 

 need to be emphasized, however. In the first place, there is no 

 doubt that in one of the first phases of fermentation, glucose, a 

 six-atomic carbon chain, breaks into two three-atomic segments. 

 This explains why only trioses, hexoses, and nonoses are fer- 

 mentable, but no pentoses or heptoses. A very important factor 

 also, is the process of reduction in alcoholic fermentation. The 

 capacity of reduction by yeast has been known for a long time. It 

 has been noted, for example, that after the addition of sublimed 

 sulphur to a fermenting liquid, hydrogen sulphide is formed. 

 Methylene blue may be reduced in the same manner to a colorless 

 leuco compound (containing 2 hydrogen atoms more than the dye 

 itself; nitrobenzole, to aniline, etc.). All these reactions indicate 

 that during fermentation activated hydrogen is formed, which 

 through a special reducing enzyme, called reductase, is transferred 

 from the substance containing hydrogen to the hydrogen acceptor, 

 such as sulphur and the other substances mentioned. In the 

 normal course of fermentation the hydrogen serves to reduce 

 acetaldehyde. 



A very interesting feature is the active part played by phos- 

 phoric acid in alcohol fermentation. It has been proven that 

 phosphates considerably accelerate the fermentation of sugar, 

 sometimes ten to twenty times. This is especially the case when 

 fermentation is produced not by yeast but by zymase. The inves- 

 tigations of L. Ivanov (1905) as well as of Harden and Young (1905) 

 have shown that during the first stages of fermentation there is 

 formed a diphosphoric ether of fructose, CeHio04(Na2P04)2, the 

 so-called zymophosphate, a special enzyme, phosphatese taking 

 part in this synthesis. With the further progress of fermenta- 

 tion, the zymophosphate splits up again under the action of the 

 same phosphatese, always producing d-fructose, no matter from 

 what fermentable hexose it was formed. The stimulating influence 

 of phosphates on fermentation has not yet been fully explained. 

 It is possible that the transformation of all hexoses into the same 

 form of d-fructose may be brought about. The most active sugar 

 taking part in all vital processes is glucose, with a closed chain 



