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CHAPTER XXII. 



GENERAL VIEW OP THE FUNCTION OP DIGESTION. OP THE MINOR 

 FUNCTIONS WHICH CONTRIBUTE TO IT. OP FOOD. ITS QUALITY. 

 ITS QUANTITY. 



HAVING discussed the great animal functions of Locomotion and 

 Innervation, we now commence the consideration of those organic 

 functions which are more directly concerned in maintaining the 

 nutrition, and, consequently, the life of the individual. 



Of the nutritive processes, the function of Digestion is clearly 

 the most prominent and most important, inasmuch as it is that 

 through which the animal is enabled to receive the aliment, and 

 to prepare it for being assimilated to, and appropriated by, the 

 various textures and organs of the body. 



Under the general expression, " function of Digestion/' must be 

 comprehended several minor processes, all tending to the same 

 object ; namely, the reduction of the food for the nourishment of 

 the body. The number of these subordinate processes varies with 

 the degree of complication of the digestive function, which is ob- 

 viously influenced by the complicated nature of the animal's body, 

 and by the part which it has to play in the oeconomy of the world. 



Taking the digestive process, in its highest degree of complexity 

 in man and the mammalia, we find that there is provision, first, for 

 the prehension of the food; secondly, for its mechanical division and 

 comminution (mastication), and for its admixture with a peculiar 

 fluid (insalivation) ; thirdly, for the conveyance of the food into that 

 portion of the alimentary canal in which its principal chemical 

 changes are to take place (deglutition)', fourthly, for the solution 

 and reduction of the food preparatory to its being brought into a 

 condition favourable to absorption (cliymificatiori) ; fifthly, for the 

 separation of a material which shall contain in a condensed form 

 the chief nutritive principles of the food, and which is easily ab- 

 sorbed into the blood (chylification)', and, lastly, for the removal of 

 such portions of the food as have not been absorbed into the system 

 during its passage along the alimentary canal (defcecation) . 



In examining the digestive process in the inferior classes of animals, various 

 modifications are found to take place in it, according to peculiarities in the 



