114 OF FOOD. 



Another necessary consideration, in estimating the value of any 

 substance as an article of food, is its digestibility. A vegetable or 

 animal tissue may contain an abundance of albuminoid or starchy 

 matter, but may be at the same time of such an unyielding consist- 

 ency as to be insoluble in the digestive fluids, and therefore useless 

 as an article of food. Bones and .cartilages, and the fibres of yellow 

 elastic tissue, are indigestible, and therefore not nutritious. The 

 same remark may be made with regard to the substances contained 

 in woody fibre, and the hard coverings and kernels of various fruits. 

 Everything, accordingly, which softens or disintegrates a hard ali- 

 mentary substance renders it more digestible, and so far increases 

 its value as .an article of food. 



The preparation of food by cooking has a twofold object : first, 

 to soften or disintegrate it, and second, to give it an attractive 

 flavor. Many vegetable substances are so hard as to be entirely 

 indigestible in a raw state. Eipe peas and beans, the different kinds 

 of grain, and many roots and fruits, require to be softened by boil- 

 ing, or some other culinary process, before they are ready for use. 

 With them, the principal change produced by cooking is an altera- 

 tion in consistency. With most kinds of animal food, however, the 

 effect is somewhat different. In the case of muscular flesh, for ex- 

 ample, the muscular fibres themselves are almost always more or 

 less hardened by boiling or roasting; but, at the same time, the 

 fibrous tissue by which they are held together is gelatinized and 

 softened, so that the muscular fibres are more easily separated from 

 each other, and more readily attacked by the digestive fluids. But 

 beside this, the organic substances contained in meat, which are all 

 of them very insipid in the raw state, acquire by the action of heat 

 in cooking, a peculiar and agreeable flavor. This flavor excites 

 the appetite and stimulates the flow of the digestive fluids, and 

 renders, in this way, the entire process of digestion more easy and 

 expeditious. 



The changes which the food undergoes in the interior of the body 

 may be included under three different heads : first, digestion, or the 

 preparation of the food in the alimentary canal ; second, assimilation, 

 by which the elements of the food are converted into the animal 

 tissues ; and third, excretion, by which they are again decomposed, 

 and finally discharged from the body. 



