CHAPTER VII. 

 FOOD. 



UNDER the term " food " are included all substances, solid or liquid, 

 necessary for nutrition. The first act of this process is the ap- 

 propriation from without of the materials of the living frame, or of 

 other substances which may be converted into them. Like the tissues 

 and the fluids, therefore, the food contains various ingredients, both 

 organic and inorganic ; and the first important fact with regard to them 

 is that no single class of these substances is sufficient to sustain life, 

 but that several must be supplied in due proportion, to maintain the 

 body in a healthy condition. 



Inorganic Ingredients of the Food. 



Inorganic substances, although they afford the necessary materials 

 for vegetation, are not sufficient for the nourishment of animals, which 

 depend for their support upon elements already combined in the organic 

 form. The inorganic matters are nevertheless essential to animal life, 

 and require to be supplied in sufficient quantity to maintain their natural 

 proportion in the animal solids and fluids. As they are generally exempt 

 from alteration in the interior of the body, and are absorbed, deposited, 

 and expelled unchanged, each one, as a rule, requires to be present under 

 its own form, and in sufficient quantity, in the food. This is especially 

 true of water and sodium chloride, both of which enter and leave- 

 the system in abundant daily quantity ; and of the calcareous salts 

 which, during the growth and ossification of the skeleton, are largely 

 deposited in the osseous tissue. The alkaline carbonates, phosphates, 

 and sulphates are partly formed within the system during the meta- 

 morphosis or decomposition of organic substances ; but their elements; 

 must of course enter the body in some form, in order to enable these 

 changes to be accomplished. 



Since water enters into the composition of every part of the body, 

 it is an important ingredient of the food. In man, it is probably the 

 most important substance to be supplied with constancy and regularity, 

 and the system suffers more rapidly when deprived of fluids, than 

 when the supply of solid food only is withdrawn. Magendie found, 

 in his experiments on dogs subjected to inanition,* that the animals 

 supplied with water alone lived six, eight, or even ten days longer 



* Comptes Rendus de 1' Academic des Sciences. Paris, tome xiii., p. 256. 



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