BUCHNER'S ZYMASE OR ALCOHOLASE. 477 



power to the action of endotryptase, which is formed in the yeast 

 cells under certain conditions, but may also disappear again. A 

 high temperature seems to assist the development and action of 

 this enzyme. Up to the present it has not been found possible to 

 separate alcoholase and endotryptase, both enzymes being 

 apparently acted on equally by favourable or unfavourable in- 

 fluences, and on this account several points still remain unsolved. 

 A. HARDEN (I.) found that serum strengthens the fermentative 

 power of yeast juice, and observed at the same time a retarding 

 influence on endotryptase (see also the remarks on quinine 

 sulphate, p. 469). 



The isolation of alcoholase is a highly important question, 

 When it is remembered that none of the other enzymes has been 

 completely isolated up to the present, a satisfactory solution of 

 this problem can hardly be expected in view of the short time that 

 has elapsed since the discovery of alcoholase. Nevertheless, a 

 certain degree of progress has been made, especially when it is 

 remembered that a highly labile substance is in question. In 

 this connection AHRENS (I.) succeeded in increasing the fermenta- 

 tive power of yeast juice by freezing out the water. Other 

 experiments in the same direction relate to precipitation with 

 alcohol, and more particularly with alcohol-ether or acetone. 

 AHRENS (I.) cooled the juice down to -2 C., and obtained by this 

 means a loose mass of ice, which consisted chiefly of pure water 

 and was separable from the liquid constituents. By repeating 

 this treatment a product of increased fermentative power was 

 obtained, and MEISENHEIMER (I.), working on the same lines, 

 found that the increase amounted to about 48 per cent, in the 

 lowermost (5th) stratum. The precipitation of yeast juice by 

 alcohol-ether or acetone has been already mentioned on p. 471; 

 but this treatment does not effect any concentration of the 

 alcoholase, the whole of the proteids being thrown down at the 

 same time. The question whether fractional precipitation would 

 furnish the desired result was examined by ALBERT and 

 BUCHNER (III.), who found that while the first precipitation 

 with a little alcohol throws down the bulk of the proteids, the 

 enzyme is also deposited, and the second precipitate, with a 

 larger amount of alcohol, is devoid of fermentative power. 

 Experiments of this kind suffer from the circumstance that the 

 precipitates are only very gradually soluble in water ; and whilst 

 it is true that solution is facilitated by an addition of glycerin, 

 the resulting advantage is slight, since all the admixtures present 

 are thrown down during the reprecipitation, and consequently no 

 concentration of the enzyme is secured. The same thing happens 

 when acetone is used as precipitant. A more favourable prospect 

 was afforded by the experiments of R. ALBERT (I.), performed 

 with extracts from sterile permanent yeast. Since this material 

 still contains the unbruised cells, and therefore the enzyme cannot 



