228 GASTRIC DIGESTION. 



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 con- 

 stituents of food and the liquids which are classed as drinks undergo in the 

 stomach are very slight. Most of these substances can hardly be said to be 

 digested ; for they are either liquid or in solution in water and are capable 

 of direct absorption and assimilation. With regard to most of the inorganic 

 salts, they either exist in small quantity in the ordinary water taken as drink 

 or are united with organic nitrogenized substances. In the latter case, they 

 become intimately combined with the organic matters resulting from gastric 

 digestion. It has been noted that the various peptones contain the same 

 inorganic salts which existed in the nitrogenized substances from which they 

 were formed. 



Some discussion has arisen with regard to the action of the fluids of the 

 stomach upon calcium phosphate and calcium carbonate, salts which are con- 

 sidered nearly if not entirely insoluble. Observations on both natural and 

 artificial digestion have shown that the calcareous constituents of bone are 

 to a certain extent dissolved in the gastric juice. Bones are digested to a 

 considerable extent in the stomach, although the greater part passes through 

 the alimentary canal and is discharged unchanged in the faeces. In the nat- 

 ural process of digestion, the solution of the calcareous constituents of bone 

 is more rapid than in artificial digestion, from the fact that the juice is being 

 continually absorbed and secreted anew by the mucous membrane of the 

 stomach. 



Duration of Gastric Digestion. Inasmuch as comparatively few articles, 

 and these belonging exclusively to the class of organic nitrogenized sub- 

 stances, are completely dissolved in the stomach, it is evident that the length 

 of time during which food remains in this organ, or the time occupied in 

 the solution of food by gastric juice out of the body, does not represent the 

 absolute digestibility of different articles. It is, nevertheless, an impor- 

 tant question to ascertain, as nearly as possible, the duration of gastric diges- 

 tion. 



There has certainly never been presented so favorable an opportunity for 

 determining the duration of gastric digestion as in the case of St. Martin. 

 From a great number of observations made on digestion in the stomach itself, 

 Beaumont came to the conclusion that " the time ordinarily required for the 

 disposal of a moderate meal of the fibrous parts of meat, with bread, etc., is 

 three to three and a half hours." The observations of F. G. Smith, made 

 upon St. Martin many years later, gave two hours as the longest time that 

 aliments remained in the stomach. In a case of intestinal fistula reported 

 by Busch, it was noted that food began to pass out of the stomach into the 

 intestines fifteen minutes after its ingestion and continued to pass for three 

 or four hours, until the stomach was emptied. 



Undoubtedly, the duration of gastric digestion varies in different individ- 

 uals and is greatly dependent upon the kind and quantity of food taken, con- 

 ditions of the nervous system, exercise etc. As a mere approximation, the 



