362 FOOD AND DIGESTION 



pancreas accomplishes its digestive action by means of the enzymes given 

 above, viz., trypsin, amylopsin, steapsin, and maltase. 



Trypsin. Trypsin is a proteolytic enzyme. Strange to say, it does not 

 exist in the fresh pancreatic juice as such, but makes its appearance only 

 when there is an admixture with the succus entericus, the secretion of the 

 mucous membrane of the intestine. The succus entericus contains an ac- 

 tivating enzyme, enterokinase, which converts the inactive and stable trypsin- 

 ogen of the pancreatic juice into the active but less stable trypsin. This fact 

 is another of the wonderful series of contributions to the exact knowledge 

 of the subject of digestion made from Pawiow's laboratories. 



Trypsin, like pepsin-hydrochloric acid, converts proteins into proteoses 

 and peptones. The change, however, does not stop here; the hydrolysis 

 with trypsin goes much further. While simple amino-acids, with the excep- 

 tion of traces of tyrosine, are not found in gastric digestions, these are rapidly 

 split off in the tryptic cleavage. Thus in tryptic digestion are formed : tyro- 

 sine, leucine, cystine, amino-valerianic acid, asparaginic acid, glutaminic 

 acid, histidine, lysine, and arginine. A portion of the protein, however, 

 is not completely broken down, the residue consisting of polypeptids 

 containing proline and phenyl-alanine combined with small amounts of 

 alanine, leucine, aspartic acid, and glutaminic acid. Glycocoll, when pres- 

 ent in the protein digested, is also combined in the resistant polypeptids. 

 Crystals of leucine and of tyrosine, especially, can be found in tryptic diges- 

 tion mixtures. The products formed from protein in tryptic digestion may 

 be given in the following graphic scheme: 



Protein 



I 



Proteoses 

 Peptones 



Polypeptids Amino-acids 



Combinations of proline, phenyl- Tyrosine, tryptophane, cystine, 



alanine and glycocoll, with rela- alanine, amino-valerianic acid, 



tively small amounts of alanine, leucine, "aspartic acid, glutam- 



leucine, asparaginic acid, and inic acid, histidine, lysine, argi- 



glutaminic acid. nine. 



>*< The ferment trypsin acts best in an akaline medium, but will act also 

 in a neutral medium, or in the presence of a very small amount of combined 

 acid; it will not work in the presence of free acid. It therefore differs from 

 pepsin in being able to act without the aid of any other substance than water. 

 In the process of tryptic digestion, protein matter does not swell up at first, 

 but seems to be corroded at once. 



