270 . DIGESTION. 



of transforming starch into sugar. 1 It has already been re- 

 marked that, with regard to this question, experiments on 

 dogs, as these animals do not naturally take starch as food, 

 do not correspond with observations on the human subject. 



The changes which vegetable acids and salts, the various 

 inorganic constituents of food, and the liquids which come 

 under the head of drinks undergo in the stomach are very 

 slight. Most of these principles 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 principles. In the latter 

 case, they become intimately combined with the organic 

 principles resulting from stomach-digestion. We have al- 

 ready seen that the various peptones have been found to 

 contain the same inorganic constituents which existed in the 

 nitrogenized principles from which they were formed. 



Some discussion has arisen with regard to the action of the 

 fluids of the stomach upon the phosphate and the carbonate 

 of lime ; salts which are considered nearly, if not entirely, 

 insoluble. The action upon these principles is interesting, 

 as they are essential constituents of the osseous tissues. Ob- 

 servations in both natural and artificial digestion have shown 

 that the calcareous constituents of bone are, to a certain ex- 

 tent, dissolved in the gastric juice. The experiments of Chos- 

 sat upon animals deprived of these principles in the food 

 demonstrated that they are absolutely necessary to proper nu- 

 trition, 2 and therefore must be dissolved somewhere in the ali- 

 mentary canal and the well-known fact that the phosphate 

 of lime is soluble in acid fluids, when it is converted into the 

 biphosphate, would point at once to the gastric juice as the 

 agent for its digestion. In fact, it has been clearly shown 

 that bones are digested to a considerable extent in the stom- 



1 See page 177. 2 See page 65. 



