20 GASTRIC DIGESTION OF PROTEINS 



in the proventricle processes of bacterial decomposition of 

 the proteins may be in play. However, even in animals with 

 simple stomachs the details of the process may show vari- 

 ations. For example, in the dog, as above mentioned, the 

 proteid catabolic products arising in the stomach consist for 

 the most part of albumoses ; while in the horse the quantity 

 of albumoses is never marked enough to permit their pre- 

 dominance over syntonins, peptones and abiuret products. 



At this point we may take up at least briefly a considera- 

 tion of the digestive ferment of the stomach, pepsin. 65 



Efforts to Isolate Pepsin. A great deal of effort has been 

 expended in attempts to isolate pepsin, 56 and an apparently 

 albumin-free ferment has a number of times been obtained, 

 although usually it is thrown down along with other precipi- 

 tates of extremely varied types. Thus in Hofmeister 's labo- 

 ratory 57 a pepsin, "albumin-free" in the ordinary sense, has 

 been produced by expression by aBuchner press from gastric 

 mucous membrane ground up with infusorial earth, filtration 

 of the fluid through a Chamberland filter, subsequent dialysa- 

 tion (Briicke's method), and displaced with an alcohol-ether 

 solution of cholesterin. The pepsin adheres to the separat- 

 ing cholesterin precipitate. By suspending the latter in 

 water and removing the cholesterin with ether, there re- 

 mains a clear fluid with active digestive power failing to 

 show protein reaction or lab activity. These occasionally 

 recurring efforts to produce "analytically pure" pepsin are 

 growing more and more infrequent, as it is gradually being 

 appreciated that at best it is a fruitless labor. Even if in the 

 end, after much care and effort, a ferment is obtained so thor- 

 oughly isolated that a protein reaction can no longer be 



"Literature upon pepsin: A. Cohnheim, NagePs Handb. d. Physiol., 2, 

 548-552, 1907; F. Samuely, Handb. d. Biochem., 1, 546, 1909; A. Bickel, ibid., 

 3', 100, 1910; C. Oppenheimer, Fermente, III. Aufl., 256-280, 1910; W. Bieder- 

 mann, 2, I. Halite, 1257-1264, 1911. 



w Recent experiments of Sundberg, Sjoquist, Mrs. Schoumow-Simonowsky, 

 Friedenthal, Pekelharing, Schrumpf and others. 



8T P. Scbrumpf, Hofmeister's Beitr., 6, 396, 1905. 



