DIGESTION IN THE STOMACH. 339 



cous membrane of the calf's digestive stomach, in cheese- 

 flaking. The acid of the natural gastric juice might itself, 

 .t is true, coagulate the casein, but neutralized gastric 

 juice still possesses this power; and, since pure solutions of 

 pepsin do not, it must be due to some third body, which has, 

 however, not yet been isolated. The curdled condition of 

 the milk regurgitated so often by infants is, therefore, not 

 any sign of a disordered state of the stomach, as nurses 

 commonly suppose. It is natural and proper for milk to 

 undergo this change, before the pepsin and acid of the 

 gastric juice convert its casein into peptone. 



Gastric Digestion. The process of swallowing is con- 

 tinuous, but in the stomach the onward progress of the 

 food is stayed for some time. The pyloric sphincter, re- 

 maining contracted, closes the aperture leading into the 

 intestine, and the irregularly disposed muscular layers of 

 the stomach keep its semi-liquid contents in constant 

 movement, maintaining a sort of churning by which all 

 portions are brought into contact with the mucous mem- 

 brane and thoroughly mixed with the secretion of its glands. 

 The gelatin-yielding connective tissue of meats is dissolved 

 away, and the proteid-containing fibres, left loose, are dis- 

 solved and turned into peptones. The albuminous walls 

 of the fat-cells are dissolved and their oily contents set 

 free; but the gastric juice does not act upon the latter. 

 Certain mineral salts (as phosphate of lime, of which there 

 is always some in bread) which arc insoluble in water but 

 soluble in dilute acids, are also dissolved in the stomach. 

 On the other hand the gastric juice has itself no action 

 upon starch, and since ptyalin does not act at all, or only 

 imperfectly, in an acid medium, the activity of the saliva 

 in converting starch is stayed in the stomach. By the solu- 

 tion of the white fibrous connective tissue, that disintegra- 

 tion of animal foods commenced by the teeth, is carried 

 much farther in the stomach, and the food-mass, mixed 

 with much gastric secretion, becomes reduced to the con- 

 sistency of a thick soup, usually of a grayish color. In 

 this state it is called chyme. This contains, after an ordi- 

 nary meal, a considerable quantity of peptones which are 



