FISSION OF SACCHARIDES. 361 



Hence the piocess appears more complicated than other fermen- 

 tations ; and, contrary to statements in the literature, no one has 

 yet succeeded in obtaining the acid by the simple oxidation of 

 sugar. 



There is little to be gained by going into the question of the 

 biological importance of such acid fermentations, since it affords 

 no explanation. Although, in the case of oxalic acid fermenta- 

 tion it might be that the accumulating acid is injurious to com- 

 petitors for the available food, this can hardly apply to citric acid 

 fermentation. In both cases the acid is lacking at the time when 

 it would be most effective, namely, at the commencement of 

 vegetation ; and where it is afterwards present in abundance, it 

 no longer possesses any value in this respect, the fungus having 

 already fully occupied the substratum. Moreover, the accumula- 

 tion injures the fungus, and finally, liquids containing citric acid 

 also permit the development of certain other fungi. A far 

 more important problem is whether the organism is not itself 

 injured by the waste of substance entailed by the accumula- 

 tion of acid, as is certainly the case, for instance, in alcoholic 

 fermentation. This does not appear to be so with oxalic acid 

 fermentation, and, according to WEIIMER (XXVIII.), it is 

 not appreciable in the case of citric fermentation, despite the 

 higher physiological value of this acid, the only way in which it 

 can be estimated being by careful quantitative determinations. 

 In genera], however, from the standpoint of practicability it 

 may be said that in the interests of the organism fermentations 

 of this kind are better dispensed with, since they imply a more or 

 less uneconomical utilisation of the substratum. 



MAZE and PERKIER (I.) have latterly occupied themselves with 

 the formation of citric acid. They observed this to occur from 

 alcohol and glycerin, and ascribe its origin to an incipient scarcity 

 of nitrogen in the culture, though it is independent of the 

 presence or absence of oxygen. The acid is said to result from a 

 process of disassimilation when the substratum has been exhausted 

 of assimilable nitrogen ; and its formation is preceded by a decom- 

 position of the sugar into alcohol and carbon dioxide. It would 

 probably be easy to refute these statements by experiment. Maze 

 and Perrier seem to be acquainted with only a preliminary com- 

 munication by WEHMER (XXX.), and not with his more exhaus- 

 tive work (XXVIII.). 



292. The Fission of Disaccharides and Trisaeeharides, 

 Glucosides and Polysaccharides (Starch Excepted). 



The inverting enzyme of the Aspergillacece was discovered a few 

 years anterior to their diastasic enzyme ; and subsequently various 

 other enzymes were recognised. Up to the present, these have 

 chiefly been detected in Asp. niger and Pen. ylauctim, the latter 



