372 FOOD AND DIGESTION 



Circumstances Influencing Gastric Digestion. A temperature of 

 about 40 C. is most favorable to gastric digestion. The pepsin is destroyed 

 by a temperature of 55 (neutral) to 65 C. (acid solution) and its action is 

 retarded and suspended by low temperatures. It is inactive in neutral 

 or alkaline solution, for an acid medium is necessary. Hydrochloric is the 

 best acid for the purpose, but other mineral acids or the organic acids may 

 be substituted for the hydrochloric. Excess of peptone delays the action, and 

 the removal of the products of digestion facilitates the process. 



Action of Rennin. Milk is curdled by the action of gastric juice, the 

 casein being first precipitated, and then dissolved. The curdling is due to a 

 special ferment of the gastric juice, rennin, and is not due to the action of the 

 free acid alone. The effect of rennin, which is obtained commercially 

 from the fourth stomach of the calf, has long been known, as it is used ex- 

 tensively to cause precipitation of casein in cheese manufacture. The fer- 

 ment rennin is active in a neutral solution as well as in acid. 



The Action of Gastric Lipase. For many years it has been known 

 that fats were digested in the stomach, but it has been a more difficult matter 

 to definitely prove the source of the lipase, most physiologists holding that 

 the lipase is regurgitated from the intestine. In 1880 Cash proved that 

 extracts of the gastric mucosa contained an active lipase which experimentally 

 caused the dissociation of neutral fats as tested by the increased amount 

 of fatty acid. He removed the pancreas and showed that fats were still 

 digested. Ogata made the tests in the living stomach of the dog, closing off 

 the opening into the intestine. The stomach thus isolated and washed out 

 with physiological saline repeatedly caused the appearance of fatty acid 

 when olein was introduced and brought into contact with the living gastric 

 mucosa. It is evident that the secretion of the gastric glands contains an 

 active lipase. 



The well known observation of Pawlow showing that the secretion of 

 pepsin is inhibited by an excess of fat in the stomach, when taken in con- 

 nection with other facts showing the specific nature of the digestive 

 secretions, see figure 268, suggests that lipase secretion may be thus 

 stimulated. 



Pancreatic Digestion in the Stomach. Boldyroff has recently shown 

 that after the ingestion of fats or fatty foods in sufficient amounts, that the 

 secretion of gastric juice is inhibited and that the presence of the pancreatic 

 and intestinal secretions can be demonstrated in the stomach contents. 



The accuracy of this observation as suggested from the preceding para- 

 graph may be held in question to some extent, since the fat enzymes are 

 present in the gastric juice itself. But that there may be regurgitation of 

 the intestinal juices into the stomach is further supported by numerous 

 clinical observations. This regurgitation may, often does, take place in 

 great amount in the later stages of gastric digestion, at the time when the 



