IO2 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



f erments, tryp&ift, 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 regard- 

 ing temperature, etc. It differs from pepsin in that its pro- 

 teolytic action is more powerful and can take place in alka- 

 line media. It will also act in neutral or weakly acid media. 

 The opinion is advanced that while the gastric juice is capa- 

 ble of converting proteids into peptones, as a matter of fact 

 it does not usually carry the process further than the pro- 

 teose stage, and thus prepares the proteoses for tryptic di- 

 gestion. 



It was seen that the successive products of pepsin-hydro- 

 chloric 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. Further- 

 more 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 iden- 

 tical in its action with ptyalin. This enzyme is very impor- 

 tant, for it has been remarked that the action of ptyalin is 

 probably rather inconsequential, and by far the greater por- 

 tion of the starch, which constitutes a large part of our ordi- 

 nary food, must be digested in the small intestine and al- 

 most entirely by amylopsin. 



Steapsin. Under the influence of steapsin neutral fats 

 take up water and undergo hydrolysis, with the production 

 of glycerine and the fatty acid corresponding to the kind 



