and "ashes."

The carbon dioxid "smoke," as we have already learned, is carried in the blood to the lungs, where it pa.s.ses off in the breath. The solid part of our body waste, or the "ashes," is of two kinds--that which can be melted in water, or is, as we say, _soluble_; and that which cannot be melted in water, or is _insoluble_. The insoluble part of our solid body waste goes into the feces and is thus disposed of.

The soluble part of the body waste goes by a somewhat more roundabout route. With the carbon dioxid it is poured by the body cells into the veins, carried to the heart, and pumped through the lungs, where the carbon dioxid is thrown off. Going back to the heart it is pumped all over the body, part of it going through a very large artery to the liver, part through two large arteries to the kidneys, part to the skin, and the rest all over the remainder of the body.

The blood goes completely round the body-circuit from the heart to the fingers and toes, and back again to the heart, in less than forty-five seconds. Practically every drop of blood in the body will be pumped through the liver, the kidneys, and the skin, about once every half minute, so that they get plenty of chance to purify it thoroughly when they are working properly.

This sounds rather complicated; but is interesting, because it shows how much of a "mind of their own" the different organs and stuffs in our bodies have, or what, in scientific language, we call "power of selection." The skin glands pick out of the blood those waste substances which they are able to get rid of. The kidneys pick out another cla.s.s of waste substances, which they are best able to deal with; while the liver which is the most important of all, attacks almost every kind of waste brought to it by the blood, and prepares it for disposal by the intestines, skin, and kidneys.

The Liver. The liver has a size to match its importance. It is the largest and heaviest gland, or organ, in the body, and weighs about three pounds, a little more than the brain. It buds off from the food tube just below the stomach, so that its waste tube, the _bile duct_--about the size of a goose quill--opens into the upper part of the intestine.

The main work of the liver is to receive the blood from all over the body and to act upon its waste substances, burning them up so that they can be taken up, and got rid of, by the glands of the skin and the kidneys. In the process it very frequently changes these waste substances from poisonous into harmless forms; and even when disease germs get into the body and infect it, the poisons, or toxins, which they pour into the blood are carried to the liver and there usually burned up, or turned into harmless substances.

The liver is, therefore, to be regarded as a great _poison filter_ for the entire body. So long as it can deal with the poisons as fast as they are formed, either by the body itself, or in the food, or by disease germs, the body is safe and will remain healthy. But if the poisons come faster than the liver can deal with them, as, for instance, when we have eaten tainted meat or spoiled fruit, or have drunk alcohol, they begin to poison our nerves and muscles, and we become, as we say, "bilious."

Our head aches, our tongue becomes coated, we have a bad taste in the mouth, we lose our appet.i.te and feel stupid, dull, and feverish.

Such waste materials as the liver cannot burn down so that the kidneys and skin can handle them, it pours out through its duct into the intestine as the bile. The bile is a yellowish-brown fluid, which a.s.sists the pancreatic juice in the digestion of the food, and helps to dissolve the fats eaten, but is chiefly a waste product. It turns green when it has been acted upon by acids, or exposed to the air. So that the bile which you throw up when you are very sick at your stomach, is green because it has been acted upon by your gastric juice.

As you will remember, the blood which comes from the stomach and bowels is carried by the portal vein to the liver first and, through that, to the heart, instead of going directly to the heart, as all the other impure blood in the body does. This is owing, in part, to the fact that this blood, being full of substances freshly taken or made from the food, is very likely to contain poisons; indeed, as a matter of fact, blood taken from these veins on its way to the liver, and injected directly into the blood vessels of an animal, acts like a mild poison.

In part, however, this blood goes first to the liver, because the liver, besides being a great blood purifier, is a "blood-maker" in the sense that it changes raw food-stuffs in the blood from the intestines into forms which are more suitable for use by the brain, the muscles, and the other tissues of the body. Some of the sugars, for instance, the liver turns into a kind of animal starch (_glycogen_), which it stores away in its own cells. It also turns both sugars and proteins in the portal blood into fat, part of which it pours into the blood, and part of which it stores away also in its own cells. Thus the liver owes its great size partly to the large amount of blood-purifying, filtering, and poison-destroying work which it has to do, and partly to its acting as a storehouse of starch and fat, which the body can readily draw upon as it needs them.

[Ill.u.s.tration: OUTLINE DIAGRAM SHOWING GENERAL PLAN AND POSITION OF BODY-MACHINERY]

As all poisons formed in, or entering, the body are brought to the liver for destruction, it is in an extremely exposed position, and very liable to break down under the attack of these poisons, whether of infectious diseases, or chloroform, or alcohol, or those formed by putrefaction in the stomach and intestines. This is why those who have lived long in the tropics and suffered from malaria, dysentery, and other infectious diseases, and those who drink too much alcohol, or have chronic indigestion, or dyspepsia, are likely to have swollen and inflamed livers.

The Gall Bladder. The liver has on its under side a little pear-shaped pouch called the _gall bladder_, in which the bile is stored before it is poured into the bowel. If this becomes inflamed by disease germs, or their poisons, in the blood, little hard ma.s.ses will form inside it, usually about the size of a grain of corn, known as _gall stones_. So long as they stay in the gall bladder, they give little trouble, but if they start to pa.s.s out through the narrow bile duct into the intestine, they cause severe attacks of pain, known as "gall-stone colic," and, by blocking up the duct, may dam up the flow of the bile, force it back into the blood again, and stain all our tissues, including our skin and our eyes, yellow; and then we say we are _jaundiced_. Jaundice may also be caused by colds or other mild infections which attack the liver and bile ducts and clog the proper flow of the bile.

The Kidneys. The kidneys are another form of blood-filter, which deal chiefly with waste stuffs in the blood left from the proteins, or Meats, of our food--meat, fish, milk, cheese, bread, peas, beans, etc. These waste-stuffs, called _urea_ and _urates_, are formed in the liver and brought in the blood to the kidneys. These lie on either side of the backbone, opposite the small of the back, their lower ends being level with the highest point of the hip-bones, nearly six inches higher than they are usually supposed to be. When you think you have a "pain across the kidneys," it is usually a pain in the muscles of the back much lower down, and has nothing to do with the kidneys at all.

A very large artery carries the blood from the aorta to each side of the kidney, and a large vein carries the purified blood back to the vena cava and heart. Two smaller tubes about the size of a crow quill, the waste pipes of the kidneys (the _ureters_), carry the water containing urea and other waste substances strained out by the kidneys and called urine, down into a large pouch, the _bladder,_ to be stored there until it can be got rid of.

[Ill.u.s.tration: THE URINARY SYSTEM

_K_, kidneys; _U_, ureters; _B_, bladder; _A_, artery; _V_, vein.]

The kidneys then are big filter-glands. They, like the lungs, are made up of a mesh, or network, of thousands of tiny tubes of two kinds, one set of tubes being blood vessels, and the other set the tiny branches of the kidney tubes which finally run together to form the ureters. The urine filters through from the spongy mesh of blood tubes (capillaries) into the kidney tubes and is poured out through the ureters. It is very important that the urine should be discharged as fast as it fills the bladder, that is, about once every three hours during the day. Nothing should be allowed to interfere with this; and whenever nature tells you that the bladder is full, it should be emptied promptly, or the poisons which nature is trying to get rid of in the urine may get back into the blood and cause serious trouble.

Diseases of the Kidneys. Naturally, the kidneys, working all the time and pouring out, as they do every day, from three to four pints of the liquid waste called urine, are subject to numerous diseases and disturbances. One of the common causes of these is failure to keep the skin thoroughly clean and healthy, as perspiration is of somewhat the same character as the urine; and if it be checked, it throws an extra amount of work upon the kidneys.

Another most important thing to keep the kidneys working well is to drink plenty of water, at least six or eight gla.s.ses a day, as well as to eat plenty of fresh green vegetables and fresh fruits, which, as we have seen, are eighty per cent water. Remember, we are a walking aquarium, and all our cells must be kept flooded with and soaked in water in order to be healthy. If the blood becomes overloaded with poisons, so much work may be thrown upon the kidneys that they will become inflamed and diseased and cannot form the urine properly; and then poisons acc.u.mulate in the system and finally produce serious illness and even death.

It was at one time believed that eating too much of certain kinds of foods, particularly those that leave much nitrogenous waste in the body, such as meat and fish, could produce a diseased condition of the kidneys, known as Bright's Disease; but we have found that the larger part of such cases are due to the attack of the germs of infectious diseases, particularly scarlet and typhoid fevers, tuberculosis, and colds. The popular impression that colds from wet feet or long drives in winter may "settle in the kidneys" is wrong, except in so far as those colds are caused by infectious germs.

Another cause of disturbance and permanent damage to the kidneys is the habitual use of alcohol. Even though this may be taken in only moderate amounts, the constant soaking of the tissues with even small amounts of alcohol may be most harmful to the kidneys, as well as to the liver.

CHAPTER XVIII

THE MUSCLES

Importance of the Muscles. It wouldn't be of much use to smell food, if we couldn't pick it up and bite it after we had reached it; or to see danger, if we were not able to move away from it. Every animal that lives, moves; and every movement, whether of the entire body from one place to another, or of parts of the body changing their relations to one another, or altering their shape, is carried out by an elastic, self-moving body-stuff, which we call _muscle_.

All the work that we do, whether in earning our living, or catching our food, or chewing it, or swallowing it and driving it through our food tube, or pumping the blood through our arteries, or drawing air into our lungs, is done by muscles. Hence, a very large part of the body has to be made of muscles. In fact, our muscles, put together, weigh almost as much as all the other stuffs in the body, making over forty per cent of our weight.

How the Muscles Act. The commonest form of muscle that we see is the red, lean meat of beef, mutton, or pork; and this will give us a good idea of how our own muscles look. All muscles, whatever their size or shape, are made up of little spindle-shaped or strap-shaped cells, or wriggling "body-cells" arranged in bands or strings. The size of a given muscle depends upon the number of cells that it contains.

The astonishing variety of movements which muscles can make is due to the fact that they have the power when stirred up, or stimulated, of changing their shape. As most of the muscle substance is arranged in bands, this change of shape on the part of the tiny cells that make up the band means that the band grows thicker and at the same time shorter,--just as a stretched rubber band does when it slackens,--so that it pulls nearer together the bones or other structures to which it is fastened at each end by fibrous cords called _tendons_, or sinews.

This shortening of the muscle band is known as _contraction_.

When you wish, for instance, to lift your hand toward your face, you unconsciously send a message from your brain down the nerve cables in your spinal cord, out through the nerve-wires of your neck and shoulder, to the big _biceps_ muscle on the front of your upper arm. This muscle then contracts, or shortens, and pulls up the forearm and hand, by bending the elbow joint. Just in proportion as the muscle becomes shorter, it becomes thicker in the middle; and this you can readily prove by grasping it lightly with your fingers when it contracts, and feeling it bulge.[22]

The food tube is surrounded with muscles, as you will remember, for moving the food along it, or churning it. These internal muscles, requiring only the presence of food to cause them to act, and not needing attention on the part of the brain or the will, are known as the _involuntary_ ("without the will") muscles.

The great group of the _voluntary_, or bone-moving muscles, which move "with the will" and are under our direct control, may be divided roughly into two divisions--those that move the trunk, or body proper, and run, for the most part, lengthwise of it; and those that move the limbs.

On the body, they may be divided into two great sheets--one running up the front, and the other up the back. When those running up the front of the body contract, they naturally bend the back, and pull the head and shoulders forward and downward. Or, as when you spring up and catch the branch of a tree or a horizontal bar with your hands, these same muscles will pull the lower part of the body and legs upward, so that you can climb into the tree.

The largest and thickest bands of these front body muscles are found over the abdomen, or stomach, where you can feel them thicken and harden when you bend your body forward and pull with your arms, as in hauling on a rope. By their pressure upon the intestines, they give the bowels valuable support, a.s.sist in their movements, and help the circulation of the blood through them; so that it is of considerable importance to keep this entire group of muscles well toned up by exercises, such as swinging your arms back over your head, and then down between your legs; bending the head and shoulders backward and forward; swinging the legs up over the body, either when hanging from a bar or lying on your back.

Proper exercising and toning up of these muscles will often cure constipation and dyspepsia, by their influence upon the bowels and stomach, and also keep one from taking on fat around the waist too rapidly.

On the back of the body, the muscle-sheet has grown into great, thick ropes of muscle on each side of the backbone, which you can feel hardening and softening in the small of the back, when you stoop down or lift weights. These are the muscles that hold the body erect, and keep the back straight when you stand, and are the largest and hardest working group of muscles in the body. Every minute that you sit, or stand, they are at work; and that is why they so often get tired out, and ache, and you say you have "a backache." They have to work harder to keep you erect or upright when you are standing perfectly still than when you walk or run, so that standing perfectly still is the hardest work you can do. Next to standing still, the hardest thing is to sit still, as you probably have found out. If it were not for these great muscles of the back and abdomen, we should double up like a jack-knife, either forward or backward, when we tried to stand up. It is not our skeleton that keeps us stiff or erect, but our muscles.

[Ill.u.s.tration: THE MUSCLE-SHEET

Showing how the muscles, overlapping and interlocking, give shape to the body.]

If you want to keep straight and erect, and thus have a good carriage, you must keep these great body muscles well trained and exercised by swinging movements, such as bending the back forward, standing with your feet apart and then swinging your head and shoulders down and between your legs; or, with your heels together, swinging your hands down till the fingers touch the ground; or by the different exercises that either bend your back, or hold it stiff and erect. Swinging from a bar, rowing, digging with a spade, chopping or sawing wood, dancing, rope-skipping, ball-playing, hop-scotch, and wrestling, all develop these muscles finely and are good for both boys and girls.

Other strands of these muscles branch out to fasten themselves to the shoulder blades and shoulders, where they help to draw the arm back as for a blow, pull the shoulders into position when you stand upright, or, when you have leaned forward and grasped something with the hand, help to pull up the arm and lift it from the ground. These muscles are quite important in holding the shoulders back and giving a good shape to the chest and good carriage of the upper part of the body and head. They are called into play in all exercises like striking, batting, tennis-playing, ball-throwing, swinging, shoveling, swimming, as well as in pulling, in lifting weights, in swinging an axe or handling a broom.

[Ill.u.s.tration: USE OF MUSCLES IN BOWLING

Showing _A_ thickening of flexors on front of arm, as forearm is swung forward, and _B_ thickening of extensors on back of arm, as forearm is swung backward.]

The muscles of the limbs are almost as numerous as those of the trunk of the body, and even more complex. Most of them, on both arms and legs, are in two great groups--one known as the "benders," or _flexors,_ which, when they shorten, bend the limb; and the other, the "straighteners," or _extensors_, which straighten or extend it.

On the front of the arm, for instance, we have the large biceps ("two-headed") muscle, which runs from the shoulder to the bone of the forearm just below the elbow and, when it shortens, bends the elbow and lifts the arm toward the body.

On the back of the upper arm is the _triceps_ ("three-headed") muscle, which is fastened at its lower end to a big spur of bone, the "point" of the elbow; when it shortens, acting lever fashion, it straightens or _extends_ the arm. If this is done quickly, the fist is swung outward with force enough to strike quite a sharp blow, though, as you know, if you wish to hit really hard, you have to strike with the weight and muscles of the full arm and the body behind it, or, as we say, "from the shoulder."

[Ill.u.s.tration: USE OF MUSCLES IN FOOTBALL

Showing _A_ thickening of flexors on front of thigh and leg, as foot is swung forward; and _B_ thickening of extensors on back of thigh and leg, as leg is swung backward.]

[Ill.u.s.tration: PATELLA AND MUSCLE