CHEMISTRY AND CHIEF PRODUCTS. 487 



NENCKI (Y.) is also of opinion that the absorption of water 

 into the sugar molecule is essential to alcoholic fermentation, and 

 gives an exhaustive description of the transformation of the sugar 

 into lactic acid. We must follow his train of thought, since 

 Buchner also has brought out a similar hypothesis with regard 

 to alcoholic fermentation. The sugar molecule a (see Formula I.) 

 takes up one molecule of water and decomposes into dioxypropionic 

 aldehyde b, and an intermediate product c, which parts with water 

 and is also transformed into dioxypropionic aldehyde d. This 

 latter reacts with water (Formula II.) and forms lactic aldehyde 

 and hydrogen peroxide, which decomposes into water and nascent 

 oxygen, the latter then oxidising the lactic aldehyde to lactic acid 

 (Formula III.). Lactic acid, however, contains the elements of 

 the chief products of fermentation, namely, alcohol and carbon 

 dioxide : 



COOH C0. 2 



CHOH = +CH 2 OH 



CF 3 CH 3 



BUCHNER and MEISENHEIMER (IV.) detected acetic acid and 

 lactic acid in their cell-less fermentation experiments (see p. 475, 

 vol. ii.). The amount of this last-named acid was determined in 

 the fresh yeast juice, the experiment being repeated after leaving 

 the juice to stand four days with and without an addition of 

 sugar. In two experiments without added sugar, the original 

 Lictic acid in the yeast juice was found to have disappeared, whilst 

 with added sugar it remained, and in one case increased by 100 

 per cent. Of course no bacteria were present in the yeast juice. 

 On adding 1.5 grm. of lactic acid to 500 c.c. of yeast juice and 

 leaving for a day, the whole of the acid disappeared ; but in other 

 experiments no diminution of the added acid occurred. Subse- 

 quently, however, in three sets of experiments the formation of 

 lactic acid was observed whether an addition of this acid had 

 been given or not the amount varying, however, in inverse ratio 

 to the quantity of acid added, owing to the adverse influence of 

 the latter, The varying behaviour of the yeast juice samples is 

 probably due to the character of the yeast, the tendency of the 

 juice to produce lactic acid increasing with the age of the yeast 

 from which it has been obtained. In cases, however, where the 

 formation of lactic acid could be observed in the absence of added 

 sugar, the result is obtained at the cost of the glycogen present 

 in the yeast (see p. 172, vol. ii.). The chief result of this experi- 

 ment is that lactic acid plays an important part in the decom- 

 position of sugar, and probably occurs, as an intermediate product, 

 in alcoholic fermentation. This phenomenon may be expressed 

 graphically by the aid of Formula IV. The sugar molecule a 

 (glucose) takes up four molecules of water set down here as 



