

PREHENSION OF FOOD. 485 



also in muscular tissue, fatty matter is an important constituent, essen- 

 tial, indeed, to the composition of those tissues ; moreover, starchy 

 and saccharine matters exist in certain organs, and are convertible, in 

 the living economy, into fat ; hence the non-nitrogenous, oleaginous, 

 and saccharine substances must, also, be regarded as nutritive or 

 plastic food. Even in young growing animal cells, fatty matter ap- 

 pears to be an essential element. Again, as regards gelatin, and the 

 gelatin-yielding tissues, which, though they contain nitrogen, have a 

 lower chemical constitution than the albuminoid substances, it is not 

 certain that they are convertible into, or capable of being made use of 

 as, nutriment for the living tissues. It is now generally denied that 

 they can be so converted into, or assimilated by, tissues which, like 

 muscle and nerve, contain syntonin and albumen ; it is even doubted 

 whether they can be directly assimilated as nutriment, even by the 

 living gelatin-yielding tissues themselves, which, of course, have an 

 identical chemical composition. Such substances may, therefore, pos- 

 sess very limited or no nutritive or plastic qualities ; and may merely 

 be oxidized in the system, like the non-nitrogenous, respiratory food. 

 The precise destination of the several elements of food is, however, 

 not completely understood ; but neither of the two kinds of food, the 

 nitrogenous, or the non-nitrogenous, is alone adequate to support ani- 

 mal or human life ; for perfect nutrition, the two must be taken to- 

 gether in certain proportions. 



The chemical composition of most of the nitrogenous and non-nitro- 

 genous proximate constituents of animal substances used as food, is 

 given in the tables at pages 84 and 85. The closely similar com- 

 position of the nitrogenous and non-nitrogenous proximate constit- 

 uents of vegetable substances used as food, is illustrated in the an- 

 nexed table (p. 486'). 



Prehension and Preparation of Food. 



In the lower animals, the important act of the prehension of food is 

 provided for, in every case, with the most admirable perfection of con- 

 trivance. In Man, however, the arm and hand are so wonderfully 

 organized for other, and higher, purposes (p. 193), that their pre- 

 hensile action, in the gathering, or preparation, of food, and its con- 

 veyance to the mouth, are, though essential, only subordinate offices of 

 the upper limb. The lips and tongue, which, in the Mammalia, are 

 devoted, mainly at least, to the taking of food, are in Man also so 

 employed ; but higher services are demanded of these parts, and we 

 are accustomed to associate their mechanism more especially with the 

 faculty of speech. Lastly, the jaws and teeth, although, in animals, 

 they frequently constitute the most important, and, in the case of the 

 lower Vertebrata, the sole organs of prehension, can hardly be said to 

 fulfil, in Man, in addition to their proper office of mastication, a pre- 

 hensile office in reference to the food. 



As regards the prehension of food, Man appears, indeed, almost at 

 a mechanical disadvantage, in comparison with the animals beneath 

 him, so far at least, as concerns any special adaptation of the parts of 



