CHAPTEE VIII. 



THE PEOCESSES OF DIGESTION AND RESORPTION. 



IN the preceding chapter we have considered the various digestive 

 fluids which are concerned in the transformation of those food- 

 stuffs that are incapable of resorption as such into material which 

 the body can utilize for purposes of nutrition, and we have seen that 

 the most important agents which are here concerned belong to the 

 class of the non-organized ferments. In the present chapter we 

 shall study the action of these various substances upon the different 

 classes of food -stuffs collectively and in somewhat greater detail, 

 and shall incidentally also consider the resorption of the final prod- 

 ucts of digestion from the gastro-intestinal canal. 



THE DIGESTION OF THE CARBOHYDRATES. 



The digestion of the carbohydrates is essentially effected in the 

 small intestine through the agency of the amylolytic ferment of 

 the pancreas, ptyalin, and the inverting ferments maltase, lactase, 

 and invertin, which are in part also furnished by the pancreas, but 

 are principally found in the enteric juice. In those animals in 

 which ptyalin occurs in the saliva, amylolysis to a certain degree 

 also takes place in the mouth and continues in the stomach for a 

 variable length of time, until the ferment is destroyed by the hydro- 

 chloric acid. 



In the majority of the purely carnivorous animals, as has been 

 pointed out, the saliva contains no digestive ferments, and, in such, 

 carbohydrate digestion takes place exclusively in the small intestine. 



Through the action of the ptyalin of the pancreatic juice or of the 

 saliva, as the case may be, the insoluble starch is first transformed 

 into soluble starch or amidulin (amylodextrin), and is then succes- 

 sively decomposed by hydrolysis into erythrodextrin, achroodextrin, 

 and maltose, as previously shown (see Saliva). 



Glycogen is similarly decomposed and, like starch, gives rise to 

 the formation of maltose. The celluloses, on the other hand, are 

 not affected by ptyalin nor, indeed, by any of the digestive fluids. 

 As we shall see, however, they undergo a certain kind of fermenta- 

 tion under the influence of various bacteria, and as a result we find 

 that in herbivorous animals, at least, only a fraction of the ingested 

 cellulose reappears in the feces. Thus far a transformation into 

 maltose or glucose has not been observed in the intestinal tract. 



The inversion of disaccharides is brought about by invertase, 



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