544 ENZYMES DECOMPOSING SACCHARIDES. 



corrected an erroneous (but by no means fundamental) error of 

 his French opponent, it did not controvert the latter's explanation 

 of the nature of autofermentation. The counter-hypothesis 

 successfully brought forward against Liebig by NAGELI and LOEW 

 (II.), namely, that yeast contains a greater amount (up to 37 per 

 cent.) of cellulose than reported by him is, however, untenable 

 for the reason that it was based on the result of analytical de- 

 terminations in which the so-called cellulose was not weighed 

 separately, but was taken in conjunction with a mixture of other 

 mucilaginous substances (see p. 175, vol. ii.), probably including 

 glycogen, which at that time had not been identified. 



After SALKOWSKI (IV.) had observed that yeast digested with 

 chloroform water does not undergo autofermentation, but yields 

 a Isevo-rotatory sugar, he arrived at the conviction that the source 

 of this sugar was to be found in glycogen. The same result was 

 attained by CREMER (I., Y. and VII.), except that this worker 

 showed the resulting sugar to consist of the dextro-rotatory 

 f-glucose. The accuracy of this latter point was subsequently 

 admitted by SALKOWSKI (IV.). 



Autofermentation, therefore, proceeds at the expense of yeast 

 glycogen, the degradation of this carbohydrate being accompanied 

 by other transformations that were formerly regarded and also 

 by KUTSCHER (II.) as autof ermentation . These phenomena 

 relate to the transformation of the nitrogen compounds. Accord- 

 ing to M. SCHENCK (I.), however, a sharp distinction must be 

 drawn between the autofermentation and the autodigestion of yeast. 

 This latter form of decomposition will be dealt with in chapter Ixvi. 

 Nevertheless, it will be advisable to mention here that aromatic 

 perfumes are formed during autofermentation, probably as a direct 

 accompaniment thereof. These fruity odours are emitted with 

 special intensity when the yeast is stored in a pressed state, a fact 

 well known in practice. Further investigations on the nature and 

 causation of these aromatic substances are desirable. 



Some particulars have already been given (p. 168 etseq., vol. ii.) 

 respecting glycogen and its hydrolysis by a yeast enzyme. This 

 latter, to which the name glycogenase, has been given, seems to 

 be incapable of diffusion through the cell membrane of the yeast, 

 its action being confined to the interior of the cell. This may be 

 concluded from the circumstance that the liberated enzyme in 

 expressed yeast juice prepares added glycogen for fermentation. 

 This glycogenase, \vhich to some extent is still of a hypothetical 

 character, is credited not merely with the faculty of hydrolysis 

 but also, in a high degree, with the power of reconstructing glycogen 

 under certain conditions. With regard to maltase and lactase it has 

 already been mentioned, on pp. 525 and 532, vol. ii.,that these two 

 enzymes are capable of producing reversion effects in addition to 

 their hydrolytic properties. The condition under which glycogen 

 increases or disappears in the yeast cell have been exhaustively 



