122 THE BODY AT WORK 



in fragments is reduced to a condition in which its digestion 

 will be readily completed by pancreatic juice. Gastric diges- 

 tion produces a much larger proportion of intermediate pro- 

 ducts, proteoses or propeptones, than does digestion in the 

 duodenum. Such intermediate products are quickly dealt 

 with by pancreatic juice. Artificial tests of relative digesti- 

 bility do not, as a rule, take the amount of propeptones formed 

 in a given time into account. When considering the digestion 

 of a typical meal, we must bear in mind that it is not the duty 

 of the stomach to pass as much sugar, peptone, and fat as 

 possible into the blood. In fact, very few of the products 

 of digestion are absorbed by the bloodvessels of the stomach. 

 The impermeability of its mucous membrane is shown by the 

 fact that hardly any of the water swallowed passes through 

 the stomach-wall. Practically all the water ingested leaves 

 the stomach through the pyloric valve. Various salts, some 

 sugar, and peptones are taken up by the vessels of the stomach ; 

 but the bulk of all the different kinds of food passes into the 

 duodenum in a semi-digested state. The function of the 

 stomach is to carry digestion through a preliminary stage. The 

 process will be completed in the small intestine. It is to be 

 noted that, although water is not absorbed by the stomach- 

 wall, alcohol passes through it with great rapidity. The same is 

 true of the various crystalline nitrogenous bodies found in 

 meat-extracts, and also of the essential principles of tea and 

 coffee, which chemically belong to the same class. All these 

 substances are degradation products of proteins produced by 

 oxidation, far advanced along the road to urea. In this selec- 

 tive absorption we see proof of the activity of the cells of the 

 mucous membrane. They take up the substances which it is 

 desirable to remove from the contents of the stomach. Some 

 may be wanted by the body for its immediate use ; others 

 are better out of the way, because they are prejudicial to the 

 progress of digestion. 



When contemplating the activity of the cells of the gastric 

 mucous membrane, we feel the need of an adjective which 

 shall express our recognition of the fact that they have a 

 power which we cannot confer upon our clumsy mechanical 

 imitation stomach. They can discriminate. " Vital " is the 

 only term available, though much abused. Using it without 



