256 A MANUAL OF VETERINARY PHYSIOLOGY 



phan, one of the end-products of the primary decomposition 

 of proteins. 



It is here desirable to draw attention to the fact that secretin, 

 enterokinase, and erepsin are all derived from the mucous mem- 

 brane of the intestinal canal, and care must be taken to avoid 

 confusing them : the second and last are ferments, secretin is 

 not. The function of secretin is to cause the production of 

 pancreatic juice, that of enterokinase is to endow one of the 

 ferments of the pancreatic juice with its remarkable proteolytic 

 properties, while erepsin breaks down albumose, and peptones 

 into amino-bodies. 



Amylopsin, the diastatic ferment, has an action on starchy food 

 similar to that of ptyalin, but more rapid and more active, for it 

 can deal with raw starch ; the final products are maltose and 

 achroodextrin. The hydrolytic action of amylopsin stops at 

 maltose and achroodextrin, but these are in turn attacked by 

 the maltase of the succus entericus, and converted into dextrose 

 before absorption. All starchy food which has escaped conversion 

 in the mouth and stomach is also acted upon in the intestines 

 by maltase. 



Lipase or Steapsin is the fat-splitting ferment of the pancreas ; 

 it possesses the remarkable power of breaking up fats into fatty- 

 acids and glycerine, and does this with the object of promoting 

 their absorption. We have learned a little of this action in 

 connection with the bile (p. 245), but must look at the matter 

 again in somewhat greater detail. The power of fats to form 

 emulsions is a valuable property in digestion. In the state of 

 emulsion the fat is very finely divided ; milk is a secretion in 

 which the fat is typically emulsified. Emulsion can also be 

 brought about by mixing fat with gum, egg-white, and soap 

 solution. The only fat emulsion received by animals as food is 

 when they are young, and it is said that the wall of the stomach 

 of young animals contains a gastric lipase which deals with this. 

 If so, this section of the alimentary canal is of great importance 

 in those animals where the pancreas is functionless in early life ; 

 but of this we have no information in herbivora, though it is a 

 natural condition in man. The fat-splitting power of pancreatic 

 lipase is very marked, but, as mentioned at p. 245, is greatly 

 increased by admixture with bile. When fats are split the fatty 

 acids unite with the alkali of the intestinal and pancreatic secre- 

 tion, and form soaps. We have seen the action of the combined 

 bile and lecithin in dissolving fatty acids and soaps, and the 

 physiological importance of this, for until solution is effected 

 absorption is impossible. Without the assistance of bile no 

 solution of fatty acids and soaps would occur as the result of 

 the action of lipase. 



