496 CHEMISTRY OF ALCOHOLIC FERMENTATION. 



yeast oxydase into aspartic acid, which is then decomposed into 

 malic acid, according to the equation : 



CH - CO(NH) CH - COOH 



2 I + 30 2 = 2 I + 2N 2 + 2H,,0 



CH(NH 2 ) - COOH CH(OH) - COOH 



Asparagin Malic acid 



Owing to the simultaneous presence of a reducing substance (see 

 chap. Ixvi.) in the yeast cell, the abstraction of the hydroxyl group 

 from the malic acid might be effected by its agency, succinic acid, 

 COOH-CH 2 -CH 2 -COOH, being thus formed. According to the 

 Griiss hypothesis, free nitrogen must be formed ; but this has not 

 yet been observed during alcoholic fermentation. With regard to 

 the quantitative proportions in which this element could appear 

 in comparison with carbon dioxide, i grm. of sugar could taking 

 Pasteur's figures as a basis yield 464 mgrms. of carbon dioxide 

 and 7.6 mgrms. of succinic acid, the formation of the latter being 

 accompanied according to the Griiss equation by the liberation 

 of 1.8 mgrm. of nitrogen. Converted into volume, these figures 

 would be equal, at 15 C. and 760 mm. pressure, to 253 c.c. of 

 carbon dioxide and 1.5 c.c. of nitrogen, or, in round numbers, 

 0.6 per cent, of the gas. PASTEUR (XXXII.), who determined 

 the carbon dioxide volumetrically, does not mention the presence 

 of nitrogen ; but he himself described the experiment as a very 

 delicate one, so that the smaller amount of nitrogen that might 

 be produced with a diminished yield of succinic acid might well 

 escape detection. In order to substantiate the Griiss hypothesis 

 it would be necessary to test the fermentation gases for the 

 presence of free nitrogen, and to show that this latter is formed in 

 direct ratio to the amount of succinic acid produced. It would 

 also have to be proved that yeast actually forms succinic acid from 

 asparagin. 



Oxalic acid is formed during fermentation by various organisms, 

 e.g., by Saccharomyces ffansenii, ZOPF (XV.) compare p. 283, 

 vol. ii. but it has not been definitely found to result from alcoholic 

 fermentation by yeast, though crystals of oxalate (see p. 118, 

 vol. ii.) are often observed when yeast is examined under the 

 microscope, their presence being ascribed by PRIOR (V.) to the 

 formation of small quantities of oxalic acid during fermentation. 

 Whether this originates in the sugar, however, or was already 

 formed in the fermented solution, is quite undecided. 



Lactic acid was discovered in certain fermentations by DUB- 

 RUNFAUT (IY.) in 1856, though it should be remembered that he 

 did not work with pure yeast, and, since lactic bacteria are abund- 

 ant, experiments of this kind, to be worthy of consideration, must 

 be performed with yeast perfectly free from bacteria. PASTEUR 

 (XXXI.) was unable to detect any lactic acid in the fermentations 

 with his pure yeast ; and only in one single instance did he men- 



