DIGESTION AND RESORPTION 97 



The products of peptic digestion are usually substances be- 

 longing to the group of derived proteins (58, 59). The first 

 product or products are substances called metaproteins, or, 

 according to the older terminology, syntonin or acid proteins. 

 By still further action there is formed a succession of proteoses 

 and from these, by subsequent cleavage, peptones. Undoubt- 

 edly the products resulting from peptic digestion contain a 

 large number of chemical individuals but for the present pur- 

 pose it. is sufficient to say that the action of pepsin and hydro- 

 chloric acid gives rise to the formation of a series of progres- 

 sively simpler, more soluble and more diffusible substances. In 

 natural digestion, the action extends in the main only as far 

 as the production of peptones, although polypeptids seem to 

 be also formed to some extent. Amino acids are not found 

 among the products of natural peptic digestion, although they 

 may be produced by the long continued action of pepsin-hy- 

 drochloric acid in artificial digestion. 



The conjugated proteins are split into their two constituents 

 and the protein portion is then acted upon like other proteins. 

 The gastric juice has no action upon the nucleic acids of the 

 nucleoproteins. 



137. Tryptic digestion. In the duodenum, the proteins 

 and the products of their peptic digestion are subjected to the 

 action of the trypsin of the pancreatic juice. This is produced 

 in the pancreas in the form of a pro-ferment or zymogen, called 

 trypsinogen. The presence of pancreatic juice in the duodenum 

 stimulates the glands of the latter to the production of the in- 

 testinal juice which Pawlow has found to contain a substance, 

 enterokinase, which activates the trypsinogen, or converts it into 

 trypsin, in some unknown manner. 



The action of trypsin, like that of pepsin, has been largely 

 studied in laboratory experiments either with extracts of the 

 pancreas or with its secretion as obtained from fistulae. Tryp- 

 sin, especially in a neutral or alkaline solution, acts upon pro- 

 teins substantially in the same manner as pepsin, causing a 

 hydrolytic cleavage and producing at first proteoses and pep- 

 tones. It acts much "more energetically than pepsin, however, 

 and carries the cleavage much further. The action of pepsin 

 substantially stops with the production of peptones. Trypsin, 

 on the other hand, produces a relatively large amount of the 



