DIGESTION IN THE INTESTINE 165 



similar to those used for studying peptic activity, e.g., Mett's 

 method, etc. 



Pancreatic juice also contains an enzyme called erepsin, which 

 acts mainly on the simpler digestion products, proteoses, pep- 

 tones and peptids, breaking them down into amino acids. Erep- 

 sin acts also on some proteins, such as casein. Thus the final stage 

 in the intestinal digestion of proteins is brought about by the 

 erepsin of the intestinal juice, or "succus entericus." An erep- 

 sin also is present in the intestinal mucosa and in fact in most tis- 

 sues. Erepsin reduces most of the protein digestive products to 

 the amino acid stage, the form in which they enter the blood. 



It is interesting that the kind of amino acids present and their 

 arrangement are important factors in determining whether or 

 not a given polypeptid will be digested by erepsin. 



Rennin. Pancreatic juice has the power of clotting milk, a 

 "rennin" action. This is thought by some authors to be due to 

 the pancreatic erepsin. 



Action on Fats. Steapsin. Pancreatic juice has the power 

 of emulsifying and splitting fats. If mixed with neutral olive 

 oil, tJie mixture quickly becomes acid. An enzyme called 

 " steapsin," a lipase, splits the neutral fat into glycerine and 

 fatty acids. Steapsin is believed to be produced by the cells of 

 the pancreas. It is by far the most important of the fat digest- 

 ing enzymes. It acts best in a weakly alkaline solution, the 

 optimum hydrogen-ion concentration being N X 10' 8 . In 

 stronger alkali, or in weak acid solution its activity is greatly 

 reduced. Bile has a very favorable effect upon the activity of 

 steapsin. This is partly due to the fact that bile emulsifies the 

 fats and thus makes them more accessible to the action of 

 steapsin, but this does not entirely explain the favorable effect 

 of bile. The bile salts evidently are the bile constituents con- 

 cerned. The liberated fatty acids combine in part with the 

 alkali present to form soaps. 



Action on Starches. Amylase or "Amylopsin." The pan- 

 creatic juice contains an enzyme "amylopsin" which acts on 

 starch and glycogen, splitting them into the dextrins and finally 



