60 GASTRIC JUICE. 



The experiments of most observers agree in showing that the 

 gastric juice exerts no perceptible action on the ordinary non- 

 nitrogenous foods. The fats may certainly, as \ve have already 

 mentioned, exert an influence on the gastric digestion, but they 

 undergo no recognizable chemical change. Starch, gum, and 

 sugar, when placed in pure gastric juice at the temperature of the 

 animal body, do not undergo any change corresponding to the 

 digestion of nitrogenous bodies. We shall return to the con- 

 sideration of mixed and natural vegetable food when we treat of the 

 process of digestion. 



If the fats exert an influence on digestion, we can hardly 

 conceive that this action is due to mere contact, and that it is 

 unaccompanied by any change in the fat itself, but the quantity 

 of fat which acts and is modified in this way in the digestive 

 process, is so minute as not to be appreciable in our analyses ; it 

 is evident that it is not in the stomach that the fats are digested. 



We have already mentioned (see p. 37) that Bernard believed 

 that he had discovered that acid saliva, like acid gastric juice, 

 digests animal food, and that alkaline gastric juice, like alkaline 

 saliva, digests starch ; this view is, however, opposed by the 

 positive experiments of Mialhe and Jacubowitsch. I have also 

 convinced myself that neither natural or artificial gastric juice, 

 even when rendered strongly alkaline, exerts any action on starch. 

 According to Jacubowitsch, saliva mixed with gastric juice con- 

 verts starch into sugar ; and I have confirmed this experiment with 

 acid, neutral, and alkaline mixtures. 



As the vegetable substances are permeated by saliva and gastric 

 juice, we find that they are softened and partially loosened in their 

 texture in the stomach ; the gastric juice here naturally exerts its 

 digestive power only on their nitrogenous constituents, while the 

 non-nitrogenous materials probably only undergo a preparation in 

 the stomach for the changes which are normally effected in the 

 small intestines. 



Pure gastric juice antagonises the ordinary processes of fer- 

 mentation, and hence lactic, acetic, and alcoholic fermentation are 

 excluded from the sphere of gastric digestion, so long as this 

 process is a normal or physiological one. At the very most only 

 a part of the cane or milk sugar introduced into the stomach can 

 be converted into glucose. 



