DIGESTION AND ABSORPTION IN THE INTESTINES. 729 



trypsin before absorption is likely to be acted upon by the erepsin 

 before reaching the blood.* Another interesting view is that sug- 

 gested by Abderhalden.t According to this author, the hydrolysis 

 of the protein by pepsin and trypsin (and perhaps by erepsin) is not 

 complete. Many amino-bodies, such as tyrosin, leucin, arginin, etc., 

 are split off from the protein molecule, but there remains behind 

 what one may call a nucleus of the original molecule, which serves as 

 the starting point for a synthesis. This nucleus is a substance or a 

 number of substances intermediate between the peptone and the 

 simpler end-products, and is spoken of as a peptid or peptoid (see 

 Appendix) . Since its structure is unknown and it is probably not 

 a simple body, it is designated as a polypeptid. Abderhalden has 

 shown that in tryptic digestion such substances are formed that 

 is, substances which are not peptones, since they no longer give the 

 biuret reaction, but which have a certain complexity of structure, 

 since upon hydrolysis with acids they split into a number of mon- 

 amino- and diamino-bodies. A schema of peptic-tryptic digestion 

 from this standpoint may be given as follows: 



Native protein. 

 Peptone. 



Polypeptid. Tyrosin, leucin, glutaminic acid, aspartic acid, 

 a-pyrrolidin carbpxylic acid, tryptophan, etc. 

 Arginin, lysin, histidin. 



From either of the points of view presented it may be suggested that 

 the value of this more or less complete splitting of the protein of the 

 food lies in the possibility that thereby the body is able to construct 

 its own peculiar type of protein. Many different kinds of proteins 

 are taken as food and many of them if introduced directly into the 

 blood act as foreign material incapable of nourishing the tissues. 

 If these proteins are broken down more or less completely during 

 digestion the tissue cells may reconstruct from the pieces a form of 

 protein adaptable to their needs. At present our knowledge of what 

 takes place during the absorption of protein is very incomplete, and 

 a satisfactory theory of protein nutrition is scarcely possible until 

 this portion of the subject is cleared up (see p. 737) . 



Action of the Diastatic Enzyme (Amylopsin) of the Pan- 

 creatic Secretion. This enzyme is found in the secretion of the 

 pancreas or it may be extracted from the gland. Its action upon 



* Vernon ("Journal of Physiology," 30, 330, 1904) believes that the 

 pancreatic secretion contains two proteolytic enzymes trypsin proper, 

 which converts the proteins to peptones, and pancreatic erepsin, which breaks 

 up the peptones into the simpler end-products, the amino-bodies. 



f Abderhalden, loc. tit. 



