552 ENDOTRYPTASE AND PHILOTHION. 



restrictive action than glycerine or glycocoll in isofconic solutions ; 

 consequently, in this case the retarding effect must not be regarded 

 as a purely physical process. 



Pressed yeast juice, concentrated to one-third its original 

 volume in vacuo, exhibited a considerably lessened auto-digestion, 

 the same effect being produced when permanent yeast was stirred 

 up to a thick pap in water, instead of being suspended therein. 

 Whether, as opined by T. GROMOW (I.), the accumulation of 

 metabolic products constituted the retarding factor has not yet 

 been proved. 



The influence of alcohol, which is always present, more or less, 

 in yeast cultures, is also a matter of practical importance. Experi- 

 ments by Geret and Hahn have demonstrated that the proteolysis 

 of expressed yeast juice is slightly retarded by the presence of 

 5 per cent, alcohol, seriously so by 10-20 per cent, (this was 

 confirmed by T. Gromow), and stopped by 30 per cent, alcohol. 

 Hence, even in the advanced stages of fermentation of wine and 

 beer, the complete suppression of the action of endotryptase by 

 alcohol can hardly be expected to occur. According to IWANOFF 

 (II.), the restriction of proteolysis during fermentation is effected, 

 not by alcohol, the action of which (see p. 477, vol. ii.), does not 

 become apparent until the concentration exceeds 4 per cent. ; but 

 by other volatile products, aldehydes and esters (fruit ethers). 

 He states that the proteids are not decomposed by fermenting 

 yeast in pure nutrient solutions ; but in the ordinary complete 

 nutrient solutions, in which all physiological processes are in full 

 swing, even a small quantity of acid phosphates, as was found by 

 Iwanoff himself, is able to entirely neutralise the restrictive action 

 of the fermentation products on proteolysis, and in fact accelerate 

 the latter. 



Weak acids favour the action of endotryptase, the optimum 

 effect being produced by the presence of 0.2 per cent, hydro- 

 chloric acid in pressed yeast juice, or by an equimolecular amount 

 of sulphuric acid, whilst the same strength of acetic acid seems to 

 act still more favourably. Boric acid (i per cent.) or sodium 

 borate (i per cent.), does not retard proteolysis, whilst borax 

 (see p. 244, vol. ii.) and all alkalis, even as weak as 0.1-0.2 per 

 cent., diminish proteolysis considerably by the neutralisation of 

 the pressed yeast juice. 



The action of endotryptase is not confined merely to the 

 nucleins of the yeast cell, but extends also to other proteids. 

 BOULLANGER (I.) and BEIJERINCK (XXXI.) observed the digestion 

 of casein by yeast ; and Beijerinck obtained a similar result with 

 glutin, albumen, and fibrin, whilst confirmation was furnished by 

 GERET and HAHN (I. and II.) in respect of casein, glutin-casein, 

 and albumen. In his experiments with pressed yeast, SCHUTZ 

 (I.) ascertained that endotryptase attacks yeast nuclein and 

 gelatin the most, euglobin and serum albumen being far less 



