FOOD. 123 



It is evident, therefore, that no single organic substance, nor even 

 any one class alone, is sufficient for nutrition. The albuminous mat- 

 ters are first in importance because they constitute the largest part 

 of the mass of the body ; and exhaustion follows more rapidly when 

 they are withheld than when the animal is deprived of other kinds of 

 alimentary matter. But starchy and oleaginous substances are also 

 requisite ; and the body feels their want sooner or later, though plenti- 

 fully supplied with albuminous food. Finally, the inorganic saline 

 matters, in smaller quantity, are also necessary to the maintenance of 

 life. In order that the animal tissues and fluids remain healthy, and 

 perform their proper functions, they must be supplied with all the in- 

 gredients necessary to their constitution ; and a man may be starved to 

 death at last by depriving him of sodium chloride or lime phosphate as 

 surely, though not so rapidly, as if he were deprived of albumen or oiL 



Composition of Different Articles of Food. 



In the most valuable and nutritious kinds of food, adopted by the 

 universal and instinctive choice of man, the carbo-hydrates, fats, albu- 

 minous and inorganic matters are all usually present in certain pro- 

 portions. 



Milk. In milk, the first food supplied to the infant, and largely 

 employed in various culinary operations, all the important groups of 

 nutritive substances are represented. It is a white, opaque fluid, con- 

 sisting, 1st, of a serous portion, with albuminous matters, sugar, and 

 mineral salts in solution, and 2d, of fatty globules suspended in the 

 watery liquid. It is this mixture of oleaginous particles with a serous 

 fluid which gives to the milk its opacity and its white color. Its rich- 

 ness in fatty matter may therefore be estimated from these physical 

 qualities. The ingredients in cow's milk are present, according to 

 Payen, in the following proportions : 



COMPOSITION OF Cow's MILK IN 1,000 PARTS. 



Water 864 



Albuminous matter 43 



Sugar of milk 52 



Fat 37 



Mineral salts 4 



1,000 



Cow's milk resembles human milk in its general characters, but con- 

 tains a larger proportion of solid ingredients, especially of the nitro- 

 genous and saccharine matters, fat being present in nearly the same 

 amount in each. Sheep and goat's milk is richer in both nitrogenous 

 and fatty matters ; while the milk of the ass and the mare contains a 

 greater abundance of sugar, but is comparatively poor in nitrogenous 

 matter and fat. The nitrogenous matter of milk consists almost entirely 

 of caseine, associated with a small proportion of albumen. Owing to 

 the relative quantity of these two substances, milk does not solidify on 

 boiling, but merely covers itself with a thin pellicle of coagulated 



