200 GASTRIC DIGESTION 



action of the stomach, then, seems to be to prepare the fats, chiefly by 

 dissolving the adipose vesicles, for the complete digestion that takes 

 place in the small intestine. 



The varieties of sugar of which glucose is the type undergo little if 

 any change in digestion and probably are to some extent directly ab- 

 sorbed by the mucous membrane of the stomach. This is not the case, 

 however, with the varieties classed with cane-sugar. It has been shown 

 that cane-sugar injected into the veins of a living animal is not assimi- 

 lated but is immediately rejected by the kidneys. When, however, it 

 has been inverted into dextrose and levulose by the action of a dilute 

 acid or by digestion in the gastric juice, it no longer behaves as a for- 

 eign substance and does not appear in the urine. Experiments have 

 shown that cane-sugar, after digestion for several hours in the gastric 

 juice, is slowly inverted. This action does not depend on any constitu- 

 ent of the gastric juice except the free acid ; and a dilute mixture of 

 hydrochloric acid had an equally marked effect. Experiments in artifi- 

 cial digestion have shown that cane-sugar is inverted by the gastric 

 juice very slowly, the action of this secretion in no way differing from 

 that of very dilute acids. In the natural process of digestion, this 

 action may take place to a certain extent ; but it is not shown to be 

 constant or important. 



The action of gastric juice, unmixed with saliva, on starch is nega- 

 tive, so far as any transformation into sugar is concerned. When the 

 starch is enclosed in vegetable cells, it is set free by the action of the 

 gastric juice on the nitrogenous parts. Raw starch in the form of 

 granules becomes hydrated in the stomach, on account of the elevated 

 temperature and the acidity of the contents of the organ. This is not 

 the form, however, in which starch usually is taken by the human 

 subject; but when it is so taken, the stomach evidently assists in pre- 

 paring it for the more complete processes of digestion that are to take 

 place in the small intestine. 



Cooked or hydrated starch, the form in which it exists in bread, 

 farinaceous preparations generally and ordinary vegetables, is not 

 affected by the pure gastric juice and passes out at the pylorus un- 

 changed. It must be remembered, however, that the gastric juice does 

 not entirely prevent a continuance of the action of the saliva ; and ex- 

 periments have shown that gastric juice taken from the stomach, when 

 it contains a notable quantity of saliva, has, to a certain extent, the 

 power of transforming starch into sugar. 



The changes which vegetable acids and salts, the various inorganic 

 constituents of 'foods and the liquids that are classed as drinks undergo 

 in the stomach are very slight. Most of these substances can hardly be 



