102 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



three very important digestive ferments, trypsin, steapsin and 

 amylopsin. - The phosphates and carbonates are plentiful and 

 give the fluid its alkaline reaction. 



Trypsin. Trypsin, like pepsin, converts proteids into pep- 

 tones. Nothing positive is known of its composition, but it is 

 possessed of the usual characteristics of enzymes regarding tem- 

 perature, etc. It differs from pepsin in that its proteolytic action 

 is more powerful and can take place in alkaline media. It will 

 also act in/neut^'aJ or weakly acid media. The opinion is ad- 

 vanced that while ihe gastric juice is capable of converting pro- 

 ftjids into pfeptones; as & matter of fact it does not usually carry 

 the process further than the proteose stage, and thus prepares 

 the proteoses for tryptic digestion. 



It was seen that the successive products of pepsin-hydrochloric 

 digestion are syntonin, primary proteoses, secondary proteoses 

 and peptones. In tryptic digestion it seems that, in the splitting 

 process, the syntonin (here alkali-albumin) and primary proteose 

 stages are omitted, and the first product is secondary proteoses, 

 which are split into peptones. Furthermore, trypsin goes a step 

 beyond with some of the peptones and converts them into 

 simpler compounds, the best known of which are leucin and 

 tyrosin. These are found normally in the intestinal canal, but 

 the physiological importance of this conversion is not apparent. 

 The opinion that it is a useless sacrifice of useful peptones does 

 not seem warranted. 



Amylopsin. The amylolytic enzyme, amylopsin, is identical in 

 its action with ptyalin. This enyzme is very important, for it has 

 been remarked that the action of ptyalin is probably rather incon- 

 sequential, and by far the greater portion of the starch, which 

 constitutes a large part of our ordinary food, must be digested 

 in the small intestine and almost entirely by amylopsin. 



Steapsin. Under the influence of steapsin neutral fats take 

 up water and undergo hydrolysis, with the production of glyc- 



