The food first renews the worn body, and then it is the renewed body which is worn again by work, yet again to be renewed. Here, indeed, is a wonderful difference between the divinely-planned mechanism and the mechanism made by human hands.
Coal does something for the steam engine besides setting it to work—it makes it warm. Soon after the fire has been lit in the furnace, the iron gets furiously hot, and the water in the boiler turns into scalding steam; all this heat really comes out of the coal. It was hidden away in the black mass, and only required that to be placed in the furnace, to be set light to, and to be blown upon by a draught of air, in order that it might be brought out and made serviceable. One pound of coal has heat enough hidden away in it to boil sixty pints of water.
But your body is too warm. And where do you think it gets its heat from? Starve yourself for a day or two, and you will find this out. You will, under such circumstances, feel colder and colder, as well as getting weaker and weaker. A good nourishing meal on the other hand, will directly make you glow with warmth. Food warms the body, as it furnishes it with strength. There is as much heat produced in your body in a single year, as would be sufficient to turn eleven tons of ice into steam; as much in a single day, as would boil eighty pints of water.
Food, then, does three distinct things for the living body, and the living body must be duly fed at proper intervals, in order that three distinct ends may be gained. It keeps the body warm. It maintains it in a state of repair, notwithstanding the wear and tear to which it is exposed while laboring. And it gives it strength and power. Weigh out two pounds of bread and meat, and look at them. The two pounds make no very great show. But eat them, and in the wonderful contrivances of your body, those two pounds of bread and meat will sustain its machinery unwasted during the exertion of a fair day’s work, and in addition to this will supply heat enough to make eighty pints of water boil, and strength enough to lift a ton weight one mile!
In order that food may render these important services, it is necessary that it shall be wisely chosen, and no less wisely used. Many men get wasting disease and death out of food, in the place of nourishment, warmth, and vigor. If we were to heap up wet sand in the furnace of the steam engine, instead of coal, fire would be smothered, and the movement of the machinery stopped. If we were to heap up gunpowder there, the whole would be blown into fragments in a moment. Or so again, the fire of the furnace might be extinguished by smothering it with too great an abundance of coal; or it might be allowed to smoulder and die out for want. Exactly in the same way the fire and strength of the living body may be smothered by a too heavy load, or by a bad kind of food. Or it may be fanned into the explosion of destructive inflammation and fever. It is important, therefore, that everyone should know what right food is, and how good food requires to be managed. When I go down to see my friend’s yarn-spinning steam engine, I find that a very great amount of care is bestowed upon its feeding. Only the most suitable coal is supplied for its consumption, and the stoker who feeds it is chosen from among his companion workmen for his judgment, and he is trained to be exceedingly careful, watching its wants, and studying its appetite, so as to give exactly what it can manage, a little and often, never allowing the furnace to be either too hungry or too much gorged.
My friend is ten times more particular about the feeding of his steam engine, than he is about the feeding of himself, and in this respect he is pretty much like the rest of mankind. Men select and regulate, with the most careful thought, what they put into the furnaces of their machinery; but into those delicate and sensible living furnaces which they carry about in their own bodies, they toss with reckless indifference, now, as it were, lumps of lead, and now explosive gunpowder. There is, indeed, sad need that men should be made more thoughtful than they are about feeding their bodies. As a guardian and supporter of the health, good food stands close by the side of fresh air and pure water. Bad feeding, on the other hand, is the ally of foul air and deficiency of water, in bringing about disorder. Improper management in feeding, then, is another way in which men lay up for themselves disease and suffering, and cause sickness to take the place of health.
Man’s food consists of an almost endless variety of substances. The surface of the earth is covered with things which man can eat, and get strength out of. This is a very bountiful arrangement, made by Divine Providence, in order that the rapidly increasing multitudes of the human race may be supported. Into whatever diversity of climate or country man can go, there he finds a rich abundance of the nourishment which the continued well-being of his body requires. In the hot tropics he gathers bread-fruit from the trees, and plucks rice from the ground. In temperate lands he covers the soil with corn, and pastures beef-yielding oxen and mutton-affording sheep upon the grass. In the frozen wastes that lie near the poles, he gets whale-blubber and seal-oil from the inhabitants of the ocean. The water teems every where with fish, the air with fowl, and the solid ground is literally painted green with fattening grass. Nearly all food substances are, however, more or less solid bodies, in order that they may be kept conveniently in store until they are immediately needed, and it is, therefore, a natural result of this arrangement that they have to undergo a sort of preparation before they can be put to use. The several parts of the body which have to be nourished are far more delicate than the finest hairs. Now suppose that you were set to get beef and bread into hairs, I fancy you would find yourself rather puzzled by the task. God however is not so puzzled. He pours beef and bread into fibres that are as much smaller than hairs, as hairs themselves are smaller than men six feet high and three feet round. You will, no doubt, like to learn how this is done.
The All-wise and Almighty Designer of life has seen fit to employ in the work an agent that is already familiar to us. This agent is pure water. God washes food into the body, exactly as he washes worn-up material out of it. The very water, indeed, which carries away the waste, has in the first instance carried in the food. God has laid down pipes of supply which run every where through the structures of the body, exactly as he has laid down the drain-pipes. These pipes branch out to the hair, the eyes, the head, the feet, the flesh, the bones, and the skin. At the beginning of the supply pipes there is a great pump always at work, pumping on the supply. This pump is called the heart. Place your hand on the left side of your chest, and you will feel how this heart is springing at its pumping work. You will be sensible that it is raising itself up at its labor, at every stroke, so determined is the exertion of its strength. The supply-pipes are termed arteries. One large arterial pipe comes out from the heart, and then sends out branches in all directions, very much like the water-pipes sent out from the great reservoir into all the houses of a town. The branch-pipes get smaller and smaller as they go from the main, until at last they are many times smaller than the smallest hair. The food that is washed through the branching supply-pipes, by the strokes of the heart, is called blood. There are about twenty pounds of blood in the body of a full grown, active man; of these twenty pounds nearly sixteen are nothing else than pure water, the other four pounds are the finely divided food which is being hurried along by the water. This then is what I mean when I say that the food is washed into the body, by the agency of water. Take the finest needle you can find, and stick its point any where into your body, and you will find that blood will rush out of the hole. This will show you what great care has been taken to send supply-pipes everywhere. There is no spot, however small, into which a needle point can be thrust without wounding a supply-pipe. When the heart pumps, red blood thus flushes through every portion of the living frame, repairing and warming it, and supporting it in its offices. But you will say I have not yet proved my case. Food is washed out of the heart to all parts of the body. This heart, however, is already in the body. There is therefore no washing of the food into the body here. It is already in, when it is pumped from the heart; but where does the heart get the blood from, which it pumps onwards? How can it be shown that the blood comes from the food? This is to be my next step. I am going on to explain to you that the heart gets its blood from the food which is eaten; that the blood indeed is finely divided food given up to the carrying power of water; food finely prepared for its task of nourishing the living frame. How then is the food thus prepared? how is solid food turned into liquid and easily flowing blood?
Food is turned into blood by being digested. Men have digesting bags, more commonly known under the name of stomachs, inside of them, into which portions of digestible substances are placed from time to time. These inside digesting bags are particularly convenient, because when a fair quantity of food is once packed away there, men may move about in pursuit of their business without having to give any further heed to the digesting work that is going on in their behoof. Before, however, food is passed down into the digesting bag, it is first ground in a powerful mill, and mixed up with liquid into a sort of paste. The mill has many pairs of very hard stones set in rows over against each other. It is called the mouth, and the stones are termed teeth. The liquid, which makes the ground food into paste, is poured out from little taps laid on in the mill or mouth, and is called the saliva.
When the ground and moistened food has been deposited in the stomach, more liquid is poured out upon it there. This liquid is termed the “gastric” or stomach juice. Next it is shaken, and churned up, and turned over by the movements of the stomach-bag. After a few hours’ churning, it has become so soft and pulpy from the soaking, that it is ready to advance another stage. Then a sort of sluice-gate at the end of the stomach is opened, and down the pulp goes into the bowel, there to be mixed with another liquid called bile, or liver juice, and the soaking or digestion is completed. The pulp then consists of two things—a white milk-like liquid; that is the rich and nourishing part of the food, ground and soaked down to the utmost fineness, and mingled with some of the water which has been drunk. And a coarse solid substance, still undigested; that is the waste part of the food which has resisted the dissolving power of the stomach, and is on its way to be rejected as good for nothing. The white milk-like essence of the food gets sucked up, by a quantity of little holes or mouths that lie all over the lining of the bowel, as the pulp moves down this canal. Then it is carried by tubes provided for the purpose into one main channel. This channel runs upwards until it ends in the great forcing pump. Poured into the heart, it reinforces the blood which it finds there, and is sent onwards with it through the supply-pipes. This is how food becomes blood.