286 DIGESTION. 



The saccharine including the amylaceous principles are at 

 first, probably, only mechanically separated from the vege- 

 table substances within which they are contained, by the 

 action of the gastric fluid. The soluble portions, viz., 

 dextrin and sugar, are probably at once absorbed. The 

 insoluble ones, viz., starch and lignin, (or some parts of 

 them) are rendered soluble and capable of absorption, by 

 being converted into dextrin or grape-sugar. It is pro- 

 bable that this change is carried on to some extent in 

 the stomach ; but this conversion of starch into sugar is 

 effected, not by the gastric fluid, but by the saliva intro- 

 duced with the food, or subsequently swallowed. The 

 transformation of starch is continued in the intestinal 

 canal, as will be shown, by the secretion of the pancreas, 

 and perhaps by that of the intestinal glands and mucous 

 membrane. The power of digesting uncooked starch is, 

 however, very limited in man and Carnivora, for when 

 starch has been taken raw, as in corn and rice, large 

 quantities of the granules are passed unaltered with the 

 excrements. Cooking, by expanding or bursting the 

 envelopes of the granules, renders their interior more 

 amenable to the action of the digestive organs ; and the 

 abundant nutriment furnished by bread, and the large 

 proportion that is absorbed of the weight consumed, afford 

 proof of the completeness of their power to make its starch 

 soluble and prepare it for absorption. 



Of the oleaginous principles, as to their changes in the 

 stomach, no more can be said than that they appear to be 

 reduced to minute particles, and pass into the intestines 

 mingled with the other constituents of the chyme. In the 

 case of the solid fats, this effect is probably produced by 

 the solvent action of the gastric juice on the areolar tissue, 

 albuminous cell-walls, &c., which enter into their com- 

 position, and by the solution of which the true fat is able 

 to mingle more uniformly with the other constituents of 

 the chyme. Being further changed in the intestinal canal, 

 fat is rendered capable of absorption by the lacteals. 



