554 SPECIAL PHYSIOLOGY. 



cleated cells. The composition of chyme, like its color, also varies 

 with the nature of the food. With ordinary diet, it consists of a mix- 

 ture of the saline, amylaceous, saccharine, albuminoid, gelatinoid, and 

 fatty matters of the food, in different conditions of conversion or solu- 

 tion. The starch, partly changed into dextrin and sugar in the mouth, 

 continues to undergo transformation in the stomach, even more rapidly, 

 because the vegetable cells are loosened or dissolved, so as to set free 

 the starch grains. The conversion of starch into sugar in the stomach 

 is due to the saliva swallowed with it, for, in an animal, ligature of the 

 oesophagus, which prevents the continued entrance of saliva into the 

 stomach, arrests this transformation. A good deal of starch always 

 passes from the stomach, undissolved. The albuminoid and gelatinoid 

 substances are represented in the chyme by albuminose or the albumen 

 and gelatin peptones; whilst the fatty matters of animal tissues, per- 

 haps to a small extent decomposed, are loosened from the fat-cells, and 

 as well as the fatty matter of butter or cheese, are reduced to minute 

 particles, intermixed with the rest of the chyme. 



The characters of the chyme depend, however, not only on solvent 

 actions, but also on the process of absorption, which begins in the stom- 

 ach as soon as that organ contains fluid or dissolved matters. Owing 

 to the escape of chyme into the intestine, the quantity actually in the 

 stomach, at any one time, is small; and, owing to absorption, the 

 quantity which passes into the duodenum is much less than the quan- 

 tity of fluid swallowed and secreted for the purposes of gastric diges- 

 tion. Even the soluble constituents of the chyme are constantly 

 being removed by absorption. The soluble constituents of our solid 

 and fluid food, such as saline matter, sugar, alcohol, and thein, and 

 also the soluble products of digestion, such as sugar, and the albumen 

 and gelatin peptones, mixed with some salivin and pepsin, are greedily 

 absorbed, with the water of the chyme, by the bloodvessels of the mu- 

 cous membrane of the stomach, and are then conveyed through the 

 portal vein, into the liver. 



The chyme itself, therefore, at any one moment, does not represent 

 the simple product of the digestion of food, but the joint product of 

 the double process of digestion and absorption. In comparison with 

 the food taken, it necessarily contains a larger proportion of fatty 

 matter than of saline, saccharine, amylaceous, albuminoid, or gelatin- 

 oid substances; for the fatty substances have undergone little or no 

 chemical change, and no absorption from the stomach, whereas the 

 others have been more or less dissolved, altered, and absorbed. 



The semifluid product is, moreover, constantly being forced for- 

 wards, drop by drop, through the pyloris into the duodenum, where it 

 undergoes further changes, now to be considered. 



Action of the Bile. 



The bile performs a most important part in the intestinal digestive 

 process; but its action does not depend on the presence of an albu- 

 minoid substance, like salivin, pepsin, or pancreatin. Its importance 

 is shown by its highly complex composition, and by its containing sub- 



