Yet during this entire time his weight may have been nearly uniform. [Footnote: If, however, he were kept on the scale pan of a sensitive balance, he would find that his weight is constantly changing, increasing with each meal, and then gradually decreasing.] Our bodies are but molds, in which a certain quantity of matter, checked for a time on its ceaseless round, receives a definite form. They may be likened, says Huxley, to an eddy in the river, which retains its shape for a while, yet every instant each particle of water is changing.
WHAT FOOD DOES.—We make no force ourselves. We can only use that which nature provides for us. [Footnote: We draw from Nature at once our substance, and the force by which we operate upon her; being, so far, parts of her great system, immersed in it for a short time and to a small extent. Enfolding us, as it were, within her arms, Nature lends us her forces to expend; we receive them, and pass them on, giving them the impress of our will, and bending them to our designs, for a little while; and then—Yes; then it is all one. The great procession pauses not, nor flags a moment, for our fall. The powers which Nature lent to us she resumes to herself, or lends, it may be, to another; the use which we have made of them, or might have made and did not, is written in her book forever.—Health and its Conditions.] All our strength comes from the food we eat. Food is force—that is, it contains a latent power which it gives up when it is decomposed. [Footnote: This force is chemical affinity. It binds together the molecules which compose the food we eat. When oxygen tears the molecules to pieces and makes them up into smaller ones, the force is set free. As we shall learn in Physics, it can be turned, into heat, muscular motion, electricity, etc. The principle that the different kinds of force can be changed into one another without loss, is called the Conservation of Energy, and is one of the grandest discoveries of modern science.—Popular Physics, pages 35, 39, 278.] Oxygen is the magic key which unlocks for our use this hidden store. [Footnote: We have spoken of the mystery that envelops the process of the conversion of food force into muscular force (note, p. 107). All physiologists agree that muscular power has its source in the chemical decomposition of certain substances whereby their potential energy is released. Probably some of the food undergoes this chemical change before it passes out of the alimentary canal; possibly some is broken up by the oxygen while it is being swept along by the blood; but, probably by far the largest part is converted into the various tissues of the body, and finally becomes a waste product only after there takes place in the tissue itself that chemical disorganization that sets free its stored-up power.— FOSTER'S Physiology.] Putting food into our bodies is like placing a tense spring within a watch; every motion of the body is only a new direction given to this food force, as every movement of the hand on the dial is but the manifestation of the power of the bent spring in the watch. We use the pent-up energies of meat, bread, and vegetables which are placed at our service, and transfer them to a higher theater of action. [Footnote: It is a grand thought that we can thus transform what is common and gross into the refined and spiritual; that out of waving wheat, wasting flesh, running water, and dead minerals, we can realize the glorious possibilities of human life.]
KINDS OF FOOD NEEDED.—From what has been said it is clear that, in order to produce heat and force, we need something that will burn, i. e., with which oxygen can combine. Experiment has proved that to build up every organ, and keep the body in the best condition, we require three kinds of food.
1. Nitrogenous Food.—As nitrogen is a prominent constituent of the tissues of the body, food which contains it is therefore necessary to their growth and repair. [Footnote: Since this kind of food closely resembles albumen, it is sometimes called Albuminous. The term Proteid is also used.] The most common forms are whites of eggs—which are nearly pure albumen; casein—the chief constituent of cheese; lean meat; and gluten—the viscid substance which gives tenacity to dough. Bodies having a great deal of nitrogen readily oxidize. Hence the peculiar character of the quick-changing, force-exciting muscle.
2. Carbonaceous Food—i. e., food containing much carbon— consists of two kinds, viz., the sugars, and the fats.
(1) The sugars contain hydrogen and oxygen in the proportion to form water, and about the same amount of carbon. They may, therefore, be considered as water, with carbon diffused through it. In digestion, starch and gum are changed to sugar, and so are ranked with this class.
(2) The fats are like the sugars in composition, but contain less oxygen, and not in the proportion to form water. They combine with more oxygen in burning, and so give off more heat.
The non-nitrogenous elements of the food have, however, other uses than to develop heat. [Footnote: The heat they produce in burning may be turned into motion of the muscles, according to the principle of the Conservation of Energy (p. 153, note); while all the structures of the body in their oxidation develop heat.] Fat is essential to the assimilation of the food, while sugar and starch aid in digestion and may be converted into fat. [Footnote: In Turkey, the ladies of the harem are fed on honey and thick gruel, to make flesh, which is considered to enhance their beauty. The negroes on the sugar plantations of the South always grow fat during the sugar-making season.] Fat and carbonaceous material both enter into the composition of the various tissues, and when, by the breaking up of the contractile substance of the muscle, their latent energy is set free, they become the source of muscular force, as well as heat. While the tendency of the albuminous food is to excite chemical action, and hence the release of energy, the fats and carbonaceous food may be laid up in the body to serve as a storehouse of energy to supply future needs.
3. Mineral Matters.—Food should contain water, and certain common minerals, such as iron, [Footnote: While the body can build up a solid from liquid materials on the one hand, on the other it can pour iron through its veins and reduce the hardest textures to blood.—HINTON.] sulphur, magnesia, phosphorus, salt, and potash. About three pints of water are needed daily to dissolve the food and carry it through the circulation, to float off waste matter, to lubricate the tissues, and by evaporation to cool the system (see p. 317). It also enters largely into the composition of the body. A man weighing one hundred and fifty-four pounds contains one hundred pounds of water, about twelve gallons—enough, if rightly arranged, to drown him. [Footnote: It is said that Blumenbach had a perfect mummy of an adult Teneriffian, which with the viscera weighed only seven and a half pounds.]
Iron goes to the blood disks; lime combines with phosphoric and carbonic acids to give solidity to the bones and teeth; phosphorus is essential to the activity of the brain. Salt is necessary to the secretion of some of the digestive fluids, and also to aid in working off from the system its waste products. These various minerals, except iron—sometimes given as a medicine, and salt—universally used as a condiment, [Footnote: Animals will travel long distances to obtain salt. Men will barter gold for it; indeed, among the Gallas and on the coast of Sierra Leone, brothers will sell their sisters, husbands their wives, and parents their children for salt. In the district of Accra, on the gold coast of Africa, a handful of salt is the most valuable thing upon earth after gold, and will purchase a slave. Mungo Park tells us that with the Mandingoes and Bambaras the use of salt is such a luxury that to say of a man "he flavors his food with salt," it is to imply that he is rich; and children will suck a piece of rock salt as if it were sugar. No stronger mark of respect or affection can be shown in Muscovy, than the sending of salt from the tables of the rich to their poorer friends. In the book of Leviticus it is expressly commanded as one of the ordinances of Moses, that every oblation of meat upon the altar shall be seasoned with salt, without lacking; and hence it is called the Salt of the Covenant of God. The Greeks and Romans also used salt in their sacrificial cakes; and it is still used in the services of the Latin church—the "parva mica" or pinch of salt, being in the ceremony of baptism, put into the child's mouth, while the priest says, "Receive the salt of wisdom, and may it be a propitiation to thee for eternal life." Everywhere and almost always, indeed, it has been regarded as emblematical of wisdom, wit, and immortality. To taste a man's salt, was to be bound by the rites of hospitality; and no oath was more solemn than that which was sworn upon bread and salt. To sprinkle the meat with salt was to drive away the devil, and to this day, nothing is more unlucky than to spill the salt.—LETHEBY, On Food.] are contained in small, but sufficient quantities in meat, bread, and vegetables.