730 PHYSIOLOGY OF DIGESTION AND SECRETION. 



starchy foods is closely similar to or identical with that of ptyalin. 

 It causes an hydrolysis of the starch with the production finally of 

 maltose and achroodextrin. Before absorption these substances are 

 further acted upon by the maltase of the intestinal secretion and 

 converted to dextrose. The starchy food that escapes digest-ion in 

 the mouth and stomach becomes mixed with this enzyme in the 

 duodenum, and from that time until it reaches the end of the large 

 intestine conditions are favorable for its conversion to maltose and 

 dextrin. Most of this digestion is probably completed, under normal 

 conditions, before the contents of the intestinal canal reach the ileo- 

 cecal valve. 



Action of the Lipolytic Enzyme (Lipase, Steapsin). The 

 importance of the pancreatic secretion in the digestion of fats was 

 first clearly stated by Bernard (1849). We know now that this secre- 

 tion contains an active enzyme capable of hydrolyzing or saponifying 

 the neutral fats. These latter bodies are chemically esters of the 

 trihydric alcohol glycerin. When hydrolyzed they break up into 

 glycerin and the constituent fatty acid. The action of lipase may 

 be represented, therefore, by the following reaction, in the case of 

 palmitin : 



C 3 H 5 (C, 5 H 31 COO) 3 + 3H 2 O = C 3 H 5 (OH) 3 + 3(C 15 H 31 COOH) 



Palmitin. Glycerin. Palmitic acid. 



When lipase from any source is added to neutral oils its splitting 

 action is readily recognized by the development of an acid reaction 

 due to the formation of the fatty acid. If a bit of fresh pancreas 

 is added to butter, for example, and the mixture is kept at the body 

 temperature the hydrolysis of the fats is soon made evident by the 

 rancid odor due to the butyric acid produced. When pancreatic 

 juice is mixed with oils or liquid fats two phenomena may be 

 noticed: first, the splitting of the fat already referred to, and, second, 

 the emulsification of the fat. The latter process is very striking. 

 An oil is emulsified when it is broken up into minute globules that do 

 not coalesce. Artificial emulsions may be made by vigorous and 

 prolonged shaking of the oil in a viscous solution of soap, mucilage, 

 etc. Milk may be regarded as a natural emulsion that separates 

 slowly on standing, as the fat rises to the top to form the cream. 

 When a little pancreatic juice is added to oil at the body temperature 

 the mixture, after standing for some time, will emulsify readily with 

 very little shaking or even spontaneously. It is now known* that 

 the emulsification is due to the formation of soaps. The lipase splits 

 some of the fats, and the fatty acid liberated combines with the 

 alkaline salts present to form soaps. The emulsification produced 



* See Ratchford, "Journal of Physiology," 12, 27, 1891. 



