204 LECTURE X. 



for instance, many albuminoids nearly immune to the action of the gastric 

 juice, which, under the influence of mineral acids in the cold, are so 

 changed that they are then appreciably disintegrated by pepsin. It 

 seems, however, that the hydrochloric acid, besides exercising this effect 

 on the albumin, also, in some manner, directly influences the pepsin. 

 This is evident from the fact, that, when all the hydrochloric acid has 

 combined with the albumin and its cleavage-products in an artificial digest- 

 ing mixture, the pepsin digestion then ceases, and can only be brought to 

 renewed activity by the addition of fresh hydrochloric acid. We are 

 justified in believing that the albumin combines with more hydrochloric 

 acid, in proportion to the greater number of cleavage-products formed. 

 Direct observation has also shown that the hydrochloric acid disappears 

 in proportion to the time of digestion. 



The breaking down of the proteins by the action of the gastric juice is 

 not at all extensive. Complicated peptones are mainly formed, accom- 

 panied, of course, by some of the lower cleavage-products, evidently of 

 the group of simple polypeptids. Amino acids, under normal condi- 

 tions, are not to be detected. 1 The digestion of albuminous substances 

 in the stomach evidently serves to prepare them for the action of 

 trypsin, with which they next come in contact. Test-tube experiments 

 have shown that tryptic digestion is quicker and more intense when 

 preceded by a pepsin-hydrochloric acid digestion. 2 Certain difficultly 

 digestible albuminous substances, as for instance serum-globulin, show 

 this property very plainly. It is evident that the preliminary digestion 

 in the stomach of the different albuminous substances is of varying 

 importance. It is of little significance for those easily digested. The 

 advantage of such a preliminary decomposition becomes especially clear 

 when we consider how rapidly the absorption of the albumin cleavage- 

 products follows in the duodenum and the remaining small intestine. 

 In spite of an extremely liberal diet of meat, we find only small amounts 

 of digesting material in the duodenum. Accordingly as the stomach 

 is emptied through the pylorus, trypsin digestion and the absorption of 

 cleavage-products take place in rapid succession. A much larger field 

 of action is presented to the trypsin ferment at one time. Instead of 

 acting upon an albumin molecule, it can immediately attack a large 

 number of cleavage-products, and quickly disintegrate them into more 

 simple components. 



The proteids, when in the stomach, are disintegrated first of all into 

 their constituents. Hematin is split off from hemoglobin, and the globin 

 is digested by itself. The nucleoproteids give off nuclein, which, being 



1 Emil Abderhalden: Z. physiol. Chem. 44, 17 (1905). 



2 Emil Fischer and Emil Abderhalden: ibid. 40, 215 (1903). 



