82 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



are formed, although the quantity of these in an ordinary gastric 

 digest is negligible. The essential difference between the two 

 enzymes is one of degree only ; trypsin is by far the more powerful 

 catalytic agent, and increases the velocity of the reaction much more 

 markedly than does pepsin-hydrochloric acid. 



2. Action of Amylopsin, The conversion of starch into maltose 

 is the most powerful and rapid of all the actions of the pancreatic 

 juice. It is much more powerful than saliva, and will act even on 

 unboiled starch. The absence of this ferment in the pancreatic juice 

 of infants is an indication that milk, and not starch, is their natural 

 diet. 



3. Action on Fats. The action of pancreatic juice on fats is a 

 double one : it forms an emulsion, and it decomposes the fats into 

 fatty acids and glycerin by means of its fat-splitting ferment steapsin. 

 The fatty acids unite with the alkaline bases to form soaps (saponified- 

 tion). The chemistry of this is described on p. 25. 



With regard to the formation of emulsions the following are the 

 principal facts. If olive oil and water are shaken up together and 

 the mixture is then allowed to stand, the finely divided oil globules 

 soon separate from and float on the surface of the water ; but if the 

 oil is shaken up with a solution of soap, the conditions of surface 

 tension are such that the oil globules remain as such in the mixture, 

 and a milky fluid or emulsion is the result. This emulsion is 

 rendered still more permanent by the presence of colloid or viscous 

 materials, especially when a small amount of free fatty acid is being 

 continually liberated. The acid combines with the alkali to form 

 a soap ; the soap probably forms a thin layer on the outside of each 

 oil globule, which prevents them running together again. Pancreatic 

 fluid possesses all the necessary qualifications for forming an 

 emulsion. It is alkaline, and it liberates fatty acids from the fat : 

 these acids form soap with the alkali present ; moreover, it is viscous 

 from the presence of protein. 



4. Milk-curdling Ferment, The addition of pancreatic extracts 

 to milk causes clotting, which differs in some of its details from the 

 curdling produced by rennin ; but this action can hardly ever be 

 called into play, as the milk upon which the juice has to act has been 

 already curdled by the rennin of the stomach. 



