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The regular exchange of matter, as we have seen, supposes the body to be a barter-place, where people take in at the same ratio they pay out. Since, however, man often pays out involuntarily and suffers so many losses – by the mere process of breathing he ejects matter which he must replace afterwards – this exchange of matter is the cause of the body's possessing the feeling of want. The body has paid out and receives nothing in return; this feeling of want is what we call "Hunger." It forces us to absorb as much as we have paid out.

Nutrition, consequently, is the continual replacing of continual losses. It is the wonderful transformation of food into the materials composing the human body.

When looking at our fellow-men, however, we must not think, that they are merely beings that have eaten food; but rather that they themselves, viz., their skin, hair, bones, brain, flesh, blood, nails, and teeth, are nothing but their own food, consumed and transformed.

CHAPTER III.

WHAT STRANGE FOOD WE EAT

Man, according to what has preceded, is nothing but transformed food.

This idea may frighten us; it may be terrible to our hearts; but let us frankly confess, it is a true one! Man consists only of such substances as he has consumed; he is, in fact, nothing but the food he has eaten; he is food in the shape of a living being.

A child is said to live on his mother's milk; but what else does this mean than: "It is mother's milk, that has become alive by having been changed into head, body, hands, feet, etc., etc."

Indeed, it may sound strange, yet it is quite correct: This mother's milk in the shape of a human being consumes again new mother's milk, and, by respiration, by evaporation and secretion of matter, casts out the used-up milk.

This being so, it will now appear evident to every one, that by a profound chemical knowledge of our daily food, we may readily learn to know the chemical components of man, and vice versâ; knowing the substances of which man is made, it is easy for us to determine, what kind of food he must take, in order to continually renew his body.

Since the mother's milk is the simplest and most natural food for the child, let us consider it according to its importance. We shall then have a stepping-stone towards the knowledge of the food of adults and its effects. The mother's milk contains all the elements, with which the human body can renew itself; should there be but one of those elements wanting in it, the child would inevitably perish.

If, for example, milk did not contain calcareous earth, the consequence would be, that the bones of the child would, soon after its birth, neither grow nor increase in number, but they would fast diminish, and the child would die in consequence of this. The attempt was once made to feed animals on articles without calcareous parts, when, strange to behold, they all grew fat, but very weak in their bones, and finally broke down.

If milk contained no phosphorus, not only would the bones and teeth suffer from the want of it, but even the completion of the child's brain could not properly take place, and the child could not replace the quantity of brain which it emits and loses every moment by breathing.

If there were no iron in the mother's milk, the child would die from the green-sickness, a malady which, by the way, is dangerous also for grown people, and which is cured by medicines containing plenty of iron.

If there were no sulphur in it, the child's bile could not develop; the bile, as every one knows, has an important function in the human body.

These are but accessory elements of the mother's milk, elements which usually are not looked upon as articles of food; for who is aware that he must eat, and actually does eat daily, phosphorus, iron, calcareous earth, and sulphur? And not only these; there are a great many other articles, such as magnesia, chlorine, and fluor, that we eat without being aware of it; moreover, our proper food consists also of three gases: nitrogen, oxygen, and hydrogen; and of a solid substance called "carbon," which is no less and no more than pure coal.

All these, my friendly readers, are contained in milk – all these are the elements which in truth constitute the human body. Perhaps some persons believe that there is nothing easier than to procure proper food. It would only be necessary to take a certain quantity of carbon, hydrogen, oxygen, and nitrogen; a little bit of potassium, natron, calcium, and magnesia; to mix a small piece of iron, sulphur, phosphorus, chlorine, and fluor, and take this mixture by the spoon at regular intervals, in order to give the body the necessary aliments. This, however, would be a mistake, for which the perpetrator would pay with his life.

Although it is true that these substances form the proper and most important constituents of our daily food; yet, in order to enjoy the desired result, we must not partake of them in their primary forms; they can actually feed our body only when they are combined together in a peculiar, wondrous manner.

In the next chapter it may be seen how nature first must combine these substances before they are presented to us as proper food; and it will also be seen, that we receive them sometimes in altogether different forms and combinations; for example, in the mother's milk, when we eat the above-named elements in the forms of caseine (cheese), butyrine (butter), sugar of milk, salt, and water.

These latter names have a more savory sound, have they not?

CHAPTER IV.

HOW NATURE PREPARES OUR FOOD

In the preceding article it was stated, that the food of the child which lives on mother's milk, consists in its primary elements of peculiar substances. These are principally oxygen, hydrogen, and nitrogen; three gases to which may be added a large quantity of carbon, or, what is the same, coal. Besides this wondrous mixture of air and coal, the mother's milk contains still other elements, but in a smaller proportion. In every-day life many of them are unfamiliar; for example, natron, calcium, magnesia, chlorine, and fluor; the others, however, are known to every one; viz., iron, sulphur, and phosphorus. All these strange ingredients nature has carefully transformed into milk. For in their primary state, and even in various chemical combinations that may be produced artificially, they would be little adapted for the purpose. It is therefore essentially necessary that nature herself should make them ready for us. This she does by letting them pass first into the vegetable state, and changing them afterwards into new forms.

The plant feeds on primary chemical elements; or, to state it more correctly, the plant is nothing but transformed primary elements! Not before the transformation of these elements into plants are the elements adapted for food for animals and men.

Moreover, all that man eats must first have been in the vegetable state. Now, it is true that man also eats the flesh, fat, and eggs of animals; but whence have the animals meat and eggs? Only from the plants they consume.

There is a remarkable succession of transformations in nature. The primary elements nourish the plant; the plant nourishes the animal; and both, plant and animal, form the nourishment of man.

Even the mother's milk, the simplest and most natural food of the child, owes its existence only to the fact that the mother has eaten vegetable and animal matter. This food, prepared for the mother by nature, has been changed into the body of the same; and partly, also, it has become the milk destined to nourish the child.

Hence it is evident that mother's milk consists of oxygen, nitrogen, hydrogen, carbon, and a small portion of other chemical primary elements. But these substances when appearing in the shape of milk, are combined in such a manner as to form ready-made food; as such they constitute, as stated above, caseine, butyrine, sugar of milk, salt, and water.

The next questions are: "What do these elements of food perform when in the child's body? What becomes of these substances after they have been eaten by the child? How are they changed during the time of their stay in the body? And in what condition do they leave the child's body, and how do they force him to desire food again?"

These questions properly belong to the chapter on "Nutrition," where they will be answered in their turn. Afterwards, we must be permitted to turn our attention to a further question, viz., "What articles of food are the most advantageous to man from the time he is weaned or the time, he takes from among vegetable and animal matter the same substances for food, that are contained in the mother's milk?"

In order to arrive at the answers to all these questions, we were obliged to first prepare the ground a little. This was a gain on our part, for now we shall attain the end in a shorter time than would have been possible otherwise. We trust that we may give our reader a correct idea of the subject, if he will but come to our aid with his most earnest attention and reflection; these are needed here the more, as we have to treat a difficult subject in a very short space.

CHAPTER V.

WHAT BECOMES OF THE MOTHER'S MILK AFTER IT HAS ENTERED THE BODY OF THE CHILD?

When the child has freed itself from the body of its mother, it consists of blood, flesh, and bones, which heretofore were formed and nourished by the blood of the mother.

As soon, however, as the child is born, it ceases to be nourished in this manner. It ceases, also, to secrete through its mother, substances which are useless to it. The child now begins to breathe for itself, and by its breath secretes carbon in the form of carbonic acid. Its skin begins to perspire, and secretes chiefly hydrogen and oxygen in the shape of water or vapor; by the urine, finally, it secretes nitrogen. These substances – carbon, hydrogen, oxygen, nitrogen – before their secretion, constituted vital parts of the child's body; now, however, they are wasted, and for this reason must be thrown off.

It is evident that the child wants compensation for this loss. This is given by the mother's milk; for it contains chiefly these same substances.

But how is this effected?

The milk passes from the child's mouth through the gullet into the stomach. While yet in the mouth, the milk is mixed with a certain liquid called saliva. This saliva possesses the quality of preparing the milk for the necessary change which will take place, when it reaches the child's stomach. The principal work, however, is carried on in the stomach itself. Its sides secrete a liquid called "gastric juice," whose business it is, to transform into a pulp milk, and also solid food, provided the latter be well masticated and moistened.

Science has taught us to prepare gastric juice artificially. The process of digestion, that is, the transformation of solid food – the crust of bread, meat, etc. – into a pulp, may nowadays be observed in a glass filled with warm, artificial, gastric juice.

After the digestion is completed, the lower opening of the stomach, which leads into the duodenum, and which, during the process of digestion, was closed by a muscle, opens itself. The pulp, now called "chyme," flows into the continuation of the stomach – the "alimentary canal" or "duodenum." This is but a long bag with many folds and windings.

The chyme is here mixed again with a liquid called "intestinal juice;" it has the quality of continuing digestion until the chyme separates into two parts; one of them, a milky fluid called "chyle," contains the substance which feeds the body. The other is the solid parts not adapted to nutrition; they are thrown out by the lower opening of the "rectum."

But how is this nutritive part, the chyle, conveyed into the various parts of the body?

The intestinal canal is filled with extremely small vessels called "lacteal absorbents." These vessels absorb the chyle. This absorption, on account of the great length of the intestinal canal – in adults it is nearly thirty feet long – is, in a healthy body, accomplished very thoroughly. The real nutriment for the body is now contained in the lacteal absorbents, an infinite number of small tubes.

All these small vessels, however, converge towards the lower part of the spinal column, and uniting, form a vessel which ascends into the chest; here it empties into a large blood-vessel, the blood of which is on its way to the heart. Thrown out of the heart in another direction, the blood is pushed through the whole body.

Thus the food, after having been transformed into a juice very similar to the blood, joins the blood after a circuitous journey, and is finally mixed with, or, more properly, changed into, blood.

CHAPTER VI.

HOW THE BLOOD BECOMES THE VITAL PART OF THE BODY

One would be well justified in calling the blood "man's body in a liquid state." For the blood is destined to become the living solid body of man.

People were astonished, when Liebig, the great naturalist, called blood the "liquid flesh;" we are correct even in going further and calling the blood "man's body in a liquid state." From blood are prepared not only muscles and flesh, but also bones, brain, fat, teeth, eyes, veins, cartilages, nerves, tendons, and even hair.

It is utterly wrong for anybody to suppose, that the constituents of all these parts are dissolved in the blood, say as sugar is dissolved in water. By no means. Water is something quite different from the sugar dissolved in it; while the blood is itself the material from which all the solid parts of the body are formed.

The blood is received into the heart, and the heart, like a pump, forces it into the lungs. There it absorbs in a remarkable manner the oxygen of the air which comes into the lungs by breathing. This blood, saturated now with oxygen, is then recalled to another part of the heart by an expansive movement of that organ.

This part of the heart contracts again and impels the oxygenated blood into the whole body by means of arteries, which branch out more and more, and become smaller and smaller, until at last they are no longer visible to the naked eye. In this manner the blood penetrates all parts of the body, and returns to the heart by means of similar thread-like veins, which gradually join and form larger veins. Having reached the heart, it is again forced into the lungs, and absorbs there more oxygen, returns to the heart, and is again circulated through the whole system.

During this double circulation of the blood from the heart to the lungs and back, and then from the heart to all parts of the body and back again – during all this, the change of particles, so remarkable in itself, is constantly going on: the exchange by which the useless and wasted matter are secreted and new substances distributed. This fact is wonderful, and its cause not yet fully explained by science; but so much is certain, that the blood when being conveyed to all parts of the human body, deposits whatever at the time may be needed there for the renewal of that part.

Thus the blood that has been formed in the child from the mother's milk, contains phosphorus, oxygen, and calcium. These substances, during the circulation of the blood, are deposited in the bones, and form "phosphate of lime," the principal element in the bone. In the same manner fluor and calcium are given to the teeth. The muscles, or flesh, also receive their ingredients from the blood; so do the nerves, veins, membranes, brain, and nails; also the inner organs, such as the heart, lungs, liver, kidneys, intestines, and stomach.

They all, however, in return give to the blood their waste particles, which it carries to that part of the human body where they may be secreted.

If any member of the body is so bound, that the blood cannot circulate, it must decay; for the life of the body consists in its constant change and transformation, in the continual exchange of fresh substances for waste ones. But this vital exchange is only kept up by the constant circulation of the blood, which, while it decreases by being transformed into vital parts of the body, is always formed anew by our daily food.

Food is therefore very justly called "Means of Existence," and the blood may rightly be called the "Juice of Life."

CHAPTER VII.

CIRCULATION OF MATTER

Thus we have seen that the human body is vital blood, transformed and solidified. Now, blood is food transformed; food consists of primary elements prepared and changed by nature; hence, man himself is primary matter transformed and vivified.

But the human race being thousands and thousands of years old, and there being upon the earth besides man the whole of the animal kingdom, developing, preserving, and nourishing itself bodily like man; the question arises: Whence do they all come, these primary elements that are obliged forever to undergo transformation before they can become animated vital matter? Do these primary elements not incessantly decrease during the long process of their being changed into plants and consumed by man and animal, in order to form human and animal bodies afterwards?

The answer to this interesting question has been given already. The human body is not framed or created anew at every moment by food; but it is at every moment, that small particles of the human body die. These particles are returned to mother earth from which they sprang, thus going back to the primary elements.

It is not only those who are dead, that render to the earth what belongs to her, that return to nature what she gave them; but in a far greater degree it is the living, that pay their debt to nature.

Man's body is not his own; nature has lent it to him but for a short term of service; then nature wrests her loan back from him. Thus must man, spite all his pride, accept her never-ceasing offer; daily he must borrow and daily he must repay in part, until the moment comes when he borrows for the last time, the moment he expires; and dying he leaves it to those around his bedside, to pay his last debt to earth.

Is it not wonderful? His own blood is the messenger that daily carries new loans to him, and, in the shape of transformed food, of transformed elements of nature, equips his body. But his own blood is at the same time also his cashier, who, having rendered him service, takes the loan away, by secreting from the body elements that are thus returned to nature.

With every revolution of the blood the body is supplied with transformed food, which is immediately changed into vital parts of the body; with every return of the blood waste matter is carried off and deposited, where it may be thrown out.

The blood carries waste matter to the kidneys that they may send out of the body, in the shape of urine, waste nitrogen, mixed with a part of the phosphate of lime, that served to form bones and teeth, but is now useless. The blood, besides, secretes perspiration through the skin. This is a liquid containing water, hence oxygen and hydrogen; but is moreover mixed with various other waste substances of the body, as for example, carbonic acid, nitrogen and fat. Chiefly, however, the blood is employed in carrying waste carbon to the lungs, so that they may, by the process of respiration, exhale carbonic acid, a gas which would prove of deadly effect if remaining in the lungs too long, or if inhaled.

The quantity of man's secretion per day is by no means small. It amounts to the fourteenth part of his own weight: nay, more – the weight of his perspiration alone, secreted partly by evaporation in the shape of gas, partly as a liquid in drops, amounts during twenty-four hours to nearly two pounds.

Secreted substances have lost all the qualities of transformed and vital matter. They return to the primary elements and serve as food principally to plants, which before had offered those very same substances as food to man.

It is in this manner that the great circulation of matter in nature takes place. From the lifeless primary elements to the plant; from the plant, in the shape of food, to animal and man; from these, as waste substances, back again to the primary elements, there to begin anew a circulation, by means of which inanimate elements are reanimated, and vital elements made lifeless again; that is, life changed again into death.

And it is in this circulation that our "Nutrition," or, more precisely, the "Change of Matter in Man," consists, an important link in the life-preserving chain of nature.

CHAPTER VIII.

FOOD

From what has been said, it must appear evident that only such dishes make good food as contain the same constituents as the blood.

To have these constituents, food must contain salt, fat, and sugar; all these ingredients must, of course, be in a certain proportion.

That water is essential for the support and renewal of the body is clear to every one. The flesh we eat, contains nearly eighty per cent. of water, and yet a man must die, if he were to eat nothing but meat and to have no water, for the reason that the eighty per cent. of water he takes in would by no means be sufficient to form all the liquids necessary for the human body.

The albumen that we eat, forms in the blood chiefly the substances composing the muscular part of the flesh. But it is an error to suppose, that therefore it is absolutely necessary to eat eggs – the white of an egg is nearly pure albumen – because the caseine (cheese) contains precisely the same ingredients as the albumen; for we have seen before, and our readers are doubtless aware of it, that the mother's milk contains caseine, while it is entirely free of albumen. Hence, he who eats plenty of caseine, as do shepherds in Switzerland, for example, scarcely needs any meat. But besides caseine there is another element, viz., the vegetable albumen called gluten, which contains albuminous matter; so do all glutinous plants. Peas, beans, and lentils in particular form food productive of flesh.

The salts that must be given to the blood, do not only consist in the common kitchen-salt. By the expression "Salts" are meant various combinations of substances which are usually not considered articles of food, for example, the combinations of phosphorus, iron, etc., but are not visible to the eye. They help to form bones, teeth, nails, cartilages, and hair.

The fat which we take, appears to many people to be a very important part of our food, and they believe that by eating much fat, one may become fat. But this is not correct. Ferocious animals that live only on meat and fat, do not get fat; while herbivorous animals fatten excessively, if provided with good mast, consisting of course but of plants. Yet fat is, for all this, by no means superfluous to our body. Man needs it, because it is the fat which chiefly supports his respiration. But the fat that is needed for the body, is formed by man himself; so that but little of it need be eaten, and that little only for the purpose of helping to form new fat from sugar.

It is therefore best to consider fat and sugar as food belonging together; for the fat is formed in the body from sugar, and the small quantity of fat which we take daily is only to promote the transformation of sugar into fat.

But let no one believe that one must needs actually eat sugar; no, every food that contains starch supplies the place of sugar very well, as starch is changed, when in the body, first to sugar and then to fat. The potato contains starch and serves its purpose well; it is necessary, however, to put butter with it in order that the starch and sugar formed from the potato in the stomach, may be easily converted into fat.

An excellent article of food is bread, for it contains nearly all the elements of nutrition. It contains vegetable albumen, and therefore is converted into flesh. It has nearly all the salts that are essential to the body; moreover, it contains starch from which fat is produced. Therefore, by the mere addition of a little butter in order to make the formation of fat easier, and by drinking water besides, the human body is able to exist. On the other hand, the potato, if taken alone, is an insufficient means of nutrition. Neither would meat or albumen, if taken alone, be able to preserve life.

Various experiments have been tried with animals, and a great deal of information about the best means of feeding the body has been collected. In order to investigate the effect of the nutritive qualities of food, inquiries have been made especially at military establishments, such as barracks, etc.