DIGESTION. 367 



sort of churning by which all portions are brought into con- 

 tact with the mucous membrane, 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 dissolved and changed. 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. Cer- 

 tain mineral salts (as phosphate of lime, of which there is 

 always some in bread) which are insoluble in water but solu- 

 ble 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 imper- 

 fectly, in an acid medium, the activity of the saliva in con- 

 verting starch is stayed in the stomach. By the solution of 

 the white fibrous connective tissue, that disintegration of ani- 

 mal 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 consistency of a thick soup, 

 usually of a grayish color. In this state it is called cliyme. 

 Chyme contains, after an ordinary meal, much peptone, though 

 some of this has been already dialyzed into the gastric mucous 

 membrane and carried off along with other dissolved dialyz- 

 able bodies, such as salts and sugar. The albumose, fats, and 

 starch still remain in the chyme. After the food has re- 

 mained in the stomach some time (one and a half to two 

 hours) the chyme begins to be passed on into the intestine 

 in successive portions. The pyloric sphincter relaxes at in- 

 tervals, and the rest of the stomach, contracting at the same 

 moment, injects a quantity of chyme into the duodenum; 

 this is repeated frequently, the larger undigested fragments 

 being at first unable to pass the orifice. At the end of about 

 three or four hours after a meal the stomach is again quite 

 emptied, the pyloric sphincter finally relaxing to a greater 

 extent and allowing any larger indigestible masses, which the 

 gastric juice cannot break down, to be driven into the in- 

 testine. 



The Chyle. When the chyme passes into the duodenum 

 it finds preparation made for it. The pancreas is in reflex 

 connection with the stomach, and its nerves cause it to qom- 

 mence secreting as soon as food enters the latter; hence a 

 quantity of its secretion is already accumulated in the intes- 

 tine when food enters. The gall-bladder is distended with 



