ENDOTRYPTASE. 557 



the enzyme-generating cells have already perished, since it may 

 be easily conceived that the death of a relatively small number of 

 cells and the enzyme to which they have given rise leads to a 

 modification of the nutrient medium or of the cell membrane of 

 the surviving cells, whereby these latter are induced to excrete 

 the enzyme. This may also perhaps explain the circumstance 

 that Will could only find relatively few dead cells in the liquefied 

 gelatin cultures. 



These statements harmonise completely with the fact that 

 Kutscher failed to detect the characteristic degradation products 

 of yeast in pure lager beer. During the actual process of fer- 

 mentation at a low temperature the number of moribund or 

 pathologically modified yeast cells will presumably be very small, 

 owing to the prevalence of the favourable environment, and con- 

 sequently the amount of endotryptase or fission products passing 

 out of the yeast cells and into the fermenting liquid will be 

 strictly limited. The conditions may, however, be entirely 

 different when the liquid is either left for a long time in contact 

 with the sedimental yeast, i.e., is not drawn off in good time, or 

 else fermentation has been conducted at a higher temperature. 

 In both cases it is not impossible for the yeast to be acted on by 

 the endotryptase (autodigestion), since both factors, prolonged 

 contact of the liquid with the sedimental yeast and high tempera- 

 ture, favour the death of the yeast cells and the action of the 

 endotryptase. Whether the increase in the proteid content, of 

 beer that has been fermented at a high temperature (20 C.), 

 as was carried out by Hantke, has any connection with this 

 subject is a matter that appears doubtful, in view of the ener- 

 getic action of endotryptase on protein, which it quickly reduces 

 to final products. On the other hand, one is bound to agree with 

 K. WINDISCH (I.) in ascribing to this cause the peculiar flavour 

 observed in low-fermentation beers that have been exposed to 

 an unduly high temperature during primary fermentation (see 

 p. 217, vol. ii.), and the flavour of digested expressed yeast juice 

 is also indicative of the same thing. 



Another important feature bearing on practice is the fact that 

 alcoholase is destroyed by endotryptase (see p. 478, vol. ii.), so 

 that in all cases where even a portion of the cells are dead, the 

 fermentative power of the yeast may suffer, especially when the 

 environment is unfavourable or the yeast is in a condition of 

 famine, such as is particularly the case when the yeast is being 

 watered or washed in the manufacture of pressed yeast. In this 

 operation, in order to free the yeast from particles of grains or to 

 classify it by sedimentation, it is left for a long time in contact 

 with cold water ; and, as a matter of fact, the makers often find 

 that the yeast is weakened, a result generally attributed to bac- 

 terial activity, to prevent which the yeast is treated with anti- 

 septics. More probably, however, the loss of fermentative power 



