DIGESTION i 9I 



transformed into maltose, passing through the intermediate stage of dextrin. 

 The process is in all respects similar to that observed in the digestion of 

 starch by saliva. Pancreatic juice, however, is more energetic in this respect 

 than saliva. The enzyme which effects this change is termed amylopsin. 

 When the starch which escapes salivary digestion passes into the small 

 intestine and mingles with pancreatic juice, it is very promptly converted into 

 maltose by the action or in the presence of this enzyme. 



2. On protein. When protein compounds are subjected to the action of 

 artificial pancreatic juice, they are transformed into peptones which do not 

 differ in essential respects from those formed by the action of gastric juice. 

 The intermediate stages, however, are believed to be somewhat different. 

 The enzyme which effects this change is termed trypsin. 



When fibrin, for example, is added to trypsin in a solution rendered 

 alkaline by sodium carbonate, it does not swell and become translucent, 

 as it does when treated with hydrochloric acid and pepsin. On the con- 

 trary, it becomes corroded on the surface, fragile, and hi a short time under- 

 goes solution. The first product is a compound termed alkali-protein. 

 After solution has taken place, various chemic changes are initiated which 

 eventuate in the production of peptone. The intermediate stages in this process 

 have not been satisfactorily determined. At no time during artificial 

 pancreatic digestion is there any evidence of the presence of the primary 

 proteoses. The secondary proteoses, however, are usually present. 



When the proteins which have escaped digestion in the stomach pass 

 into the small intestine and mingle with the pancreatic juice, they are 

 doubtless digested in the course of the intestinal canal, passing through the 

 stages just described. When proteins are artificially digested for a long 

 time there appears a number of compounds such as leucin, tyrosin, aspartic 

 acid, arginin, etc., which are representatives of a group of simple chemical 

 substances known as amino-acids. It would appear that the pancreatic 

 juice had the power under such circumstances of reducing the proteoses or 

 the peptones to their ultimate constituents. Whether this is due to the action 

 of trypsin or to the action of another enzyme erepsin is not very clear. 



The'action of trypsin on proteins in an alkaline medium may be illustrated 

 by the following scheme: 



Protein 



Alkali-protein 



Proteoses secondary 



Peptone 



Leucin Tyrosin Aspartic acid Arginin Ammonia 



The view that the final stage in the digestion of proteins is the formation 

 of peptones, which in due time are absorbed and synthesized into blood 

 albumin, has been generally abandoned for there is an ever increasing 

 evidence that the final stage is the formation of the nitrogen-holding com- 

 pounds above mentioned; in other words, that the cleavage of the proteii 

 is far more complete than has heretofore been assumed. Indeed : 

 believed that they are reduced, if not to their ultimate constituents, the 

 amino- and diamino-acids, at least to one or more of the different polypepti 



