THE NON- VOLATILE BY PRODUCTS. 495 



Exhaustive researches on succinic acid were undertaken by 

 A. RAU (II.), who, for the most part, employed 15 per cent, solu- 

 tions of saccharose, glucose, and maltose, with or without nutrient 

 substances. Three different yeasts were employed, at tempera- 

 tures of 15, 25, and 35 0., air being excluded in some cases; 

 and the principle of intermittent fermentations also applied. The 

 results showed that the total acidity is considerably increased 

 at the higher temperatures, no alteration in this respect being 

 obtained by the addition of nutrient substances. No great fluc- 

 tuation was observed in the content of succinic acid, nor does the 

 yield appear to be seriously influenced by the kind of sugar, or 

 the presence or absence of air or of yeast foods. Pure yeast and 

 pressed yeast, with vigorous fermentative power, gave a higher 

 yield of succinic acid than ordinary beer yeast. The formation of 

 the acid goes on, par i passu, with the production of alcohol and 

 decomposition of the sugar. With intermittent fermentation, 

 and at 35 C., however, the ratio of alcohol to succinic acid was 

 100:0.439; but in the three subsequent pauses the ratio was 

 100 : 0.875, IO : *89, and 100 : 0.823 respectively, or practically 

 identical. A comparison of the production of glycerine and suc- 

 cinic acid shows that low temperature, whilst unaffecting the 

 formation of the acid, restricts that of glycerine. The presence or 

 absence of nutrient substances has no influence on the production 

 of the acid, whereas providing the yeast with abundant nutrition 

 causes an increase in the yield of glycerine. (This excessive feed- 

 ing of the yeast probably leads to an accumulation of fat, which i 

 afterwards decomposed see p 494, vol. ii.). The production of 

 succinic acid is independent of that of gl} cerine, and Pasteur's 

 equation (see p. 490, vol. ii.) is inapplicable. This view of the for- 

 mation of succinic acid is also shared by STRAUB (I.). DUCLAUX 

 (XXVI.) attributes it (like glycerine) to the action of a separate 

 enzyme, but adduces no proof in support of the hypothesis. 



Succinic acid is produced in fermentation with expressed yeast 

 juice. In one case, reported by BUCHNER and RAPP (X.), 

 1250 c.c. of the juice contained 0.2 grm. of the acid before 

 fermentation, but after the fermentation of 100 grms. of sac- 

 charose, the amount was found to be 0.5 grm., an increase 

 of 0.3 grm. 



Opinions are still divided with regard to the source of succinic 

 acid, most workers regarding sugar as the raw material as in the 

 case of glycerine though it is worthy of note that the amount of 

 this acid produced under different conditions of fermentation is 

 invariably small. The amount of succinic acid present in beer 

 is also small, i.e., 0.0026-0. 0039 per cent, according to STRAUB (I.). 

 BLUMENTHAL (I.) states that micro-organisms produce this acid 

 from both carbohydrates and protein, on which account GRUSS (II.) 

 believes that the source, in the latter case, is to be found inasparagin, 

 the assumption being that this substance is first transformed by 

 VOL. ii : PT. 2 21 



