DIGESTION AND ABSORPTION IN THE STOMACH. 697 



have described other enzymes in the gastric juice or gastric mem- 

 brane, a lipase or fat-splitting enzyme (Volhard), an amylolytic 

 or starch-splitting enzyme (Friedenthal), and an inverting enzyme 

 (Widdicombe) , but the normal existence or at least the normal action 

 of these latter enzymes in digestion is a matter about which little is 

 known. As was said above, it is probable that the ptyalin swallowed 

 with the food continues to exert its action upon the starchy materials 

 in the fundus for a long time, so that in this way the starch digestion 

 in the stomach may be important. Regarding the fats, it is usually 

 believed that they undergo no truly digestive change in the stomach. 

 They are set free from their intimate mixture with other food- 

 stuffs by the dissolving action of the gastric juice upon proteids, 

 they are liquefied by the heat of the body, and they are disseminated 

 through the chyme in a coarse emulsion by the movements of the 

 stomach. In this way they are mechanically prepared so that the 

 subsequent action of the pancreatic juice is much favored. When, 

 however, fats are ingested in emulsified form, as in milk, for 

 instance, the lipase of the stomach, according to Volhard, may cause 

 a marked hydrolysis. It is supposed that this action may be impor- 

 tant in the digestion of the milk-fat by infants. Regarding the 

 proteids, the practical point of interest is how far they are digested 

 during their stay in the stomach. It seems probable that this 

 question does not admit of a categorical answer, that is, the extent 

 of the digestion varies under different circumstances, with the 

 consistency of the food, the duration of its stay in the stomach, 

 etc. In the liquid material (chyme) forced through the pylorus 

 into the duodenum one may find unchanged proteids, primary 

 or secondary proteoses, peptones, or even the final split products 

 of proteolytic action. The true value of peptic digestion is not 

 so much in its own action as in its combined action with the 

 trypsin of the pancreatic juice. The digestion of the proteids of 

 the food is effected by both enzymes, and normally we are justified 

 in considering them together as forming a peptic-try ptic digestion. 

 The preliminary digestion in the stomach is important as regards the 

 proteid foods from several standpoints: First, in the matter of 

 mechanical preparation of the food and its discharge in convenient 

 quantities easily handled by the duodenum. Second, in the more 

 or less complete hydrolysis to peptones and proteoses whereby the 

 action of the pancreatic juice must be greatly accelerated. Indeed, 

 in some cases this preliminary action of the pepsin-hydrochloric acid 

 may be absolutely necessary. Native proteids, such as serum- 

 albumin, are not acted upon by trypsin, but if submitted first to 

 pepsin-hydrochloric acid they are quickly digested by this enzyme. 

 Third, for some as yet unknown reason proteids submitted to peptic 

 digestion are split by the trypsin in a way different from its action 



