556 ENDOTRYPTASE AND PHILOTHION. 



observations, which need not be investigated more closely here, 

 Will formed the conclusion that air played a direct or indirect 

 part in proteolysis by yeast, inasmuch as the presence of air either 

 hinders the formation of a proteolytic enzyme, or destroys the 

 same when already existing. According to Will, the liquefaction 

 of gelatin is a function, not of moribund and decomposing cells, 

 but of the normal cell, and is caused by a deficiency of nutriment, 

 not merely a lack of dissolved substances in general, but of 

 nitrogenous substances in particular, and of oxygen. Whereas 

 Will regards dead yeast cells as merely an invariable concomitant 

 of proteolysis, and denies the existence of any connection between 

 proteolysis and the death of the cells, BEIJERINCK (XXXI.) 

 assumes that the enzyme originates exclusively in cells that have 

 perished in consequence of a scarcity of oxygen. Geret and 

 Hahn, however, were able to show that lack of oxygen is not 

 a decisive factor in the formation of the enzyme, inasmuch as 

 they obtained an actively digestive expressed juice from fresh 

 surface cultures of low-fermentation' beer yeast, grown on wort 

 agar-agar, under which conditions there was no lack of oxygen. 

 Even fresh yeast cells, in all stages of growth, furnish leucin and 

 other fission products, not only in the aqueous extract, but also in 

 the fresh expressed juice, the proteid derivatives in the fresh cells 

 being distributed among bases and ammo acids in the same 

 proportion as in the completely digested expressed juice. Hence, 

 a proteolytic enzyme, or the zymogen of same, is present in yeast 

 cells under all conditions ; and, as opined by Kutscher, this 

 enzyme probably exercises constructive functions, i.e., it lessens 

 the amount of the nitrogenous foodstuffs, prepared by the 

 proteolytic enzymes of malt and diffused in the yeast cells, to such 

 an extent that they can be utilised by the yeast cells for the 

 elaboration of structural materials. Consequently the proteo- 

 lytic enzyme is present as an intracellar inhabitant of every yeast 

 cell. 



The problem of the conditions under which the excretion of the 

 enzyme occurs still remains to be discussed. That deprivation 

 of oxygen does not form the decisive factor in this case also is 

 most easily concluded from the circumstance that when the living 

 cells are washed and lixiviated with distilled water, and are then 

 left for twelve hours at the bottom of the vessel, this yeast, in a 

 state of starvation as regards oxygen, cedes to the water an 

 inverting enzyme, but not a proteolytic enzyme. On the other 

 hand, the excretion of the enzyme and the process of autodiges- 

 tion begin when the yeast is left without nitrogenous nutriment 

 for some considerable time at a high temperature. In these 

 circumstances, the corporeal substance of the starving yeast is 

 attacked by the enzyme, probably the cell membrane first of all, 

 the enzyme then acting destructively, as stated by Kutscher. 

 It is, however, unnecessary to assume with Beijerinck that all 



