( 287 ) 



albumen after some hours, had lost not only the peptic but also the 

 curdling power. Indeed, the same negative result had already been 

 arrived at by Jacoby, who for these experiments did not use hen's 

 albumen but caseine '). 



In the second place it was examined whether a separation into two 

 enz vines could be brought about by dialysis. When pepsin, dissolved 

 in hydrochloric acid, is dialyzed against distilled water, it is partly 

 precipitated, most completely at a low temperature, as soon as the 

 quantity of acid has gone down to about 0.02° /„ HC1. Always, however, 

 a considerable part remains dissolved, which, with the aid of annuo- 

 nium-sulfate — if the solution does not contain much albumose 

 through 50% saturation with this salt — can be precipitated. If pepsin 

 and chymosin are different matters, it cannot be deemed improbable 

 that they also differ in solubility, that therefore the precipitate in 

 the dialyser should contain more of either one or the other matter 

 than the liquid filtered from it. Also in this way, however, a sepa- 

 ration into two enzymes, did not succeed. 



Schmidt — Nielsen, however, has communicated experiments from 

 which it appears that, though not a complete, still a partial separation 

 of pepsin and chymosin is possible. A strongly active extract from 

 the mucous membrane of the calf-stomach, prepared with hydrochloric 

 acid, was divided into two parts. One was preserved at a low tem- 

 perature, the other at 37° C. After some days the heated part had 

 for the greater part lost its power to curdle milk, under a neutral 

 reaction ; at acid reaction, however, protein was still strongly digested. 

 Now both liquids were neutralized and the one not heated so much 

 diluted that the curdling power had become as weak as that of the 

 one heated. After that the two liquids were rendered equally acid 

 with hydrochloric acid and digested with fibrine. The fibrine was 

 much quicker dissolved by the heated liquid than by the diluted 

 one, not heated. During the process of heating, therefore, the chymosin 

 had been chiefly lost, the pepsin however not. 



This experiment would certainly be convincing, if the neutralization 

 had the same effect on the heated liquid as on the one not heated. 

 This, however, is not the case. The extract contains substances 

 protecting the enzym from the action of alkali; also when no more 

 of this is added than what is necessary to attain a neutral reaction. 

 If the extract is preserved at a low temperature, these substances 

 remain for a long time undisturbed, but if the acid extract is heated 

 to 37° C, they are destroyed. Gewin has proved this by ample 

 experiments, of which a detailed account is given elsewhere. At the 



!) Biochem. Zeitschr. Bd. I, S. 66. 



