CHEMICAL CONSTITUTION OF FOOD. 481 



imate organic compounds out of their component elements, or from 

 the simpler combinations of these. 



Animals, indeed, are either carnivorous or herbivorous. The car- 

 nivorous, or flesh-devouring species, obviously live upon food possess- 

 ing the same chemical composition as the fluids and tissues of their 

 own bodies; and as regards the herbivorous, or vegetable-feeding ani- 

 mals, their food also contains proximate principles, closely resembling 

 those which exist in the animal body. Whatever the nature or source 

 of the food of Animals, its proximate principles are, therefore, chemi- 

 cally similar; and it is to the Vegetable Kingdom that we must at- 

 tribute the power of chemically combining, under the agency of solar 

 light and heat, the elements derived from the simpler combinations of 

 inorganic nature, into those complex organic proximate principles 

 which, thus elaborated in the living tissues of vegetables, constitute 

 the nutriment of Animals. Hence, the Vegetable Kingdom derives 

 its nourishment from, and depends upon, the Mineral Kingdom; the 

 Animal Kingdom derives its nourishment from, and depends upon, the 

 Vegetable Kingdom ; whilst the decaying portions of the Vegetable 

 Kingdom which are unconsumed by animals, and the particles of the 

 bodies of animals which undergo change during life, or decomposition 

 after death, revert to the simpler chemical compounds of inorganic 

 nature, which, again, under the influence of the vito-chemical forces 

 of the plant, are reintroduced into the stream of organic existence. 



Sources, Varieties, and Nature of Human Food. 



The food of Man may be either solid or fluid. If solid, it may be 

 hard, so as to require to be broken by mastication, or soft, so as merely 

 to need subdivision, before it is swallowed. Again, food may be de- 

 rived from the inorganic or from the organic world ; or it may be 

 classified according to its source, whether this be mineral, vegetable, or 

 animal. Thus, the alkaline and earthy salts, the traces of iron, sul- 

 phur, and phosphorus, and the large quantity of water, are derived 

 from the mineral kingdom. Vegetable food includes the roots, stems, 

 leaves, fruits, and seeds of plants ; also certain products of vinous de- 

 composition, as the various alcoholic beverages, and lastly, condiments, 

 vegetable acids, and vinegar or the product of the acetous fermenta- 

 tion. Animal food consists of all the digestible parts of animals, in 

 which is comprised nearly every tissue, with the exception of the 

 horny textures and the hair, even the bones yielding nutriment on 

 being boiled. Besides this, eggs and roe, milk, butter, buttermilk, 

 curd, cheese, and whey, are comprehended in this category. 



The chemical constitution of food, however, is the point to which the 



freatest significance is to be attached ; and the most useful classi- 

 cations are founded on a consideration of the different nutrient 

 proximate chemical principles which it contains. Thus regarded, the 

 multitudinous articles of diet consumed by man, under his extremely 

 varied conditions of life, dependent on climate, social condition, na- 

 tional custom, or individual habit, consist of a comparatively small 

 number of proximate chemical constituents. The importance of these 



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