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UNDER the general term of Nutrition may be comprised the various various functions and operations through the agency of which the animal economy is developed, its waste is repaired, and its heat is maintained.

animated nature, During foetal life

Life begins in man, as in all by a cell or a series of cells. the materials of nutrition are elaborated and supplied by the mother. But from the moment that parturition has taken place, that the link which united mother and child has been severed, and that the latter begins to live an independent existence, its nutrition must be the result of the action of its organization upon "the materials of nutrition " supplied from the outer world.

The materials of nutrition are obtained from



the atmospheric air breathed and from the food consumed. Out of these materials the organization of the new-born child, perfect in itself, but rudimentary in its development, has to be increased, completed, and repaired.

The human frame is composed, chemically speaking, of gases, Oxygen, Hydrogen, and Nitrogen, of Carbon, Phosphorus, Sulphur, Silicon Chlorine, Fluorine, Potassium, Sodium, Calcium, Magnesium, and Iron. These various substances exist in different states of combination. They are the chemical elements which are eliminated from the air and from food.

The nutritive elements supplied by the atmosphere which surrounds the earth, through the function of respiration, are always the same; the atmosphere being chemically composed of oxygen, nitrogen, and carbonic acid, combined with minute proportions of other gases, such as ammonia and sulphuretted hydrogen. If the atmosphere is pure, they are supplied in the same proportions. They are beyond our control, inasmuch as respiration is carried on from birth to death independently of the will.

Food contains the required chemical elements of nutrition in variable proportions, and instinct guides man and all animated beings in the choice of the kind of food required by his and their organizations. This instinct, however, may be, and often is, marred or perverted in man. The food-instinct is not so

strong with him as it is with the brute creation, the members of which generally limit themselves to the kind of food upon which nature has intended them to live and thrive. Perhaps it is so because he has reason to guide and direct him. It therefore behoves man to make use of his reason, to study himself, and thus to enable his intellect to direct his appetites and food-desires.

The body is principally formed of the three gases above enumerated, oxygen, hydrogen, and nitrogen, and of carbon transformed and solidified by nature's chemistry. The inorganic salts occupy a subordinate but indispensable position. These salts are mainly employed in forming and giving solidity to the tissues, bones, cartilages, and muscles. They are contained in greater or less, but in sufficient quantity, in the various articles of food consumed by animated beings. Thus they enter the economy with the food, imperceptibly, mysteriously, as it were, perform their duty, and are eliminated, without the individual having to look for them, or being conscious, indeed, of their presence, or of the inorganic requirements of his own organization.

In the vegetable world, carbon is the all-important and predominating elementary substance. Hydrogen and oxygen also exist in abundance, either united as water, or in other forms of combination. Nitrogen is scarcely found in some vegetable productions, and seldom constitutes more than

from 1 to 4 per cent. of the whole, even in the vegetable substances which contain it in the largest proportion, such as wheat, oats, hay, etc. In the animal world, nitrogen appears to be in the ascendant, and to constitute the most important element in the animal formation; carbon, oxygen, and hydrogen occupying a secondary position.

Even in the animal creation, however, carbon constitutes the greater part of the bulk. Thus lean beef, white of egg, and the curd of milk, when quite dry, present the following proportions (Professor Johnston):

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The greater amount of nitrogen contained in animal substances, as compared with vegetable, appears, however, to thoroughly modify their anatomical and physical character, and warrants the distinction generally recognized and established between carbonaceous and nitrogenous, or vegetable and animal, organizations.

This simple fact is at the bottom of the entire theory of nutrition in the organic creation. The framework of an animal being to a considerable

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