A Handbook of Health Part 17

_P_, patella (knee cap); _M_, muscle; _L_, ligament; _T_, tendon.]

In the lower limbs, the muscles are larger because they have heavier work to do, supporting and moving the whole weight of the body; but they are simpler in their arrangement since they have not such a variety of movements to carry out. The princ.i.p.al muscle in the thigh is the great muscle running down the front of the thigh, and fastening to the upper border of the _patella_, or knee cap. This muscle, when it shortens, straightens or extends the limb, or lifts the foot from the ground and swings it forward as in walking, or raises the knee up toward the body when we are sitting or lying down. You can easily tell how much it is used in walking by remembering how stiff and sore it gets when you have taken an unusually long tramp, particularly if there has been much hill-climbing in it. On the back of the thigh, runs another great group of muscles, which bend or flex the limb when they shorten. When the knee is bent, you can feel their tendons, or sinews, stand out as hard cords beneath the knee; hence, this group is called the _ham-string_ muscles.[23]

How the Muscles are Fed. Our muscles are not only the largest, but the "livest" part of our bodies. Their contractions and movements are caused by their tiny "explosions" (like the chugging of an automobile, except that we can't hear them); and in this way they burn up the largest part of the food-fuel which we eat--mostly in the form of sugar. When they have burned up their surplus food-fuel, they call for more; and when this demand has been telegraphed to the brain, we say we are hungry, and that exercise has given us an appet.i.te. While the muscles are at work, they demand that large supplies of fresh fuel shall be brought to them through the blood vessels; and this makes the heart beat harder and faster, and improves the circulation. As they burn up this fuel, they form smoke and ashes, or waste materials, which must be got rid of--the fluid part by perspiration from the surface of the skin, and through the kidneys, and the gas, or "smoke," through the lungs. This is the reason why, during exercise, we breathe faster and deeper than at other times, and why our skin begins first to glow and then to perspire.

If these waste-materials form in the muscles faster than the blood can wash them out, they poison the muscle-cells and we begin to feel tired, or fatigued. This is why our muscle-cells are often so stiff and sore next morning after a long tramp, or a hard day's work, or a football game. A hot bath or a good rub-down takes the soreness out of the muscles by helping them to get these poisonous wastes out of their cells.

Thus when we play or run or work, we are not only exercising our muscles and making them gain strength and skill, but we are stirring up, or stimulating, almost every part of our body to more vigorous and healthful action.

Indeed, as our muscles alone, of all our body stuffs, are under the control of the will, our only means of deliberately improving our appet.i.tes, or strengthening our hearts or circulation, or invigorating our lungs, or causing a large part of our brains and minds to grow and develop, is through muscular exercise. This is why nature has taken care to make us all so exceedingly fond of play, games, and sports of all sorts, in the open air, when we are young; and, as we grow older, to enjoy working hard and fighting and "hustling," as we say; and that is the reason, also, why we are now making muscular exercise such an important part of education.

FOOTNOTES:

[22] The muscle does not get any bigger when it contracts, as was at one time supposed; if you were to plunge it into a bath of water, and then cause it to contract, you would find that it did not raise the level of the water, showing that it was of exactly the same size as before, having lost as much in length as it gained in thickness.

[23] In the leg below the knee, and in the forearm, we have two groups of "benders" or _flexors_, and "straighteners" or _extensors_, as in the upper arm and leg, only slenderer and more numerous. They taper down into cord-like tendons at the wrist and ankle to fasten and to pull the hands and feet "open" and "shut," just as do the strings in the legs and arms of a puppet or mechanical doll, or the sinews in the foot of a chicken.

CHAPTER XIX

THE STIFFENING RODS OF THE BODY-MACHINE

What Bones Are. The bones are not the solid foundation and framework upon which the body is built, as they are usually described. They are simply a framework of rods and plates which "petrified," or turned into spongy limestone after the body was built, to make it firmer and stiffen it for movement. All the animals below the fishes, such as worms, sea-anemones, oysters, clams, and insects, get along very well without any bones at all; and when we are born, our bones, which haven't fully "set" yet, are still gristly and soft. The cores of the limbs, as they begin to stiffen, first turn into gristle, or cartilage, and later into bone; indeed, many of our bones remain gristle in parts until we are fifteen or sixteen years of age. This is why children's bones, being softer and more flexible than those of grown-up people, are not so liable to break or snap across when they fall or tumble about; and why, too, they are more easily warped or bent out of shape through lack of proper muscular exercise and proper food.

Bones are strips of soft body-stuff soaked with lime and hardened, like bricklayer's mortar, or concrete.[24] When you know the shape of the body, you know the bones; for they simply form a sh.e.l.l over the head and run like cores, or piths, down the centre of the back, and down each joint of the limbs.

In turning into spongy limestone, or animal concrete, they have become one of the deadest tissues in the body. They are tools of the muscles, the levers by which the muscles move the limbs and body about; they never do anything of their own accord. On account of their lifelessness and lack of vitality, they are rather easily attacked by disease, or broken by a blow or fall. There are such a large number of bones (two hundred and six, all told), and they resist decay and last so much longer after death than any other parts of the body, that they fill our museums and text-books of anatomy, form most of our fossils, and have thus given us rather an exaggerated idea of their importance during life.

[Ill.u.s.tration: THE HUMAN SKELETON]

The Frame-Work of the Body. Just look at any part of the body and imagine that it has a bony core of about the same general shape as itself, and you can reason out all the bones of the skeleton. To begin at the top, the _skull_ is a box of strong, plate-like bones, which have hardened to protect the brain as it grew; and the shape of its upper, or brain, part is exactly that of the head, as you can easily feel by laying your hands upon it. Then come bony sh.e.l.ls, or sockets, for the eyes and nose; and, below these, two heavy half-circles of bone, like the jaws of a steel trap, to carry the teeth.

The thickness of the lower jaw and the size and squareness of the angle where it bends upward to be hinged to the skull, below the ear, are what give the appearance of squareness and determination to the faces of strong, vigorous men or women. If we want to imply that a person has a feeble will, or weak character, we say he has a "weak jaw."

The skull rests upon the top of the backbone, or _spinal column_, which, instead of being one long solid bone, is made up of a number of pieces, or sections, known as _vertebrae_. Each one of these vertebrae has a ring, or arch, upon its back. These, running one after the other, form a jointed, bony tube to protect the _spinal cord_, or main nerve-cable of the body, which runs through it.

[Ill.u.s.tration: THE SPINAL COLUMN

_V_, vertebra; _C_, cartilage protecting spinal cord; _A_, point of articulation on the right side.]

Although the backbone can bend forward or backward, or twist from side to side a little, by the little pieces of bone of which it is built up gliding and turning upon one another, it is really very stiff and rigid, so as to protect the spinal cord and prevent its being stretched or pinched. Most of the movements which we call bending the spine are really movements of other joints which connect the body or head with it. When we bend our necks, for instance, we hardly bend the backbone at all, as most of the movement is made in the joint at the top of it, between it and the skull. Similarly, when we bend our backs, we really bend our backbones very little; for most of the movement comes at the hip joints, between the thighs and the hip bones.

Each of the limbs has a single, long, rounded bone in the upper part, known in the arm as the _humerus_, and two bones in the lower part.

These last are known as the _radius_ and _ulna_ (the "funny bone") in the forearm, and the _tibia_ and _fibula_ in the leg. The shoulder-joint is made by the rounded head of the humerus fitting into the shallow cup of the _scapula_, or shoulder-blade. It is shallower than the hip joint to allow it freer movement; but this makes it weaker and much more easily dislocated, or put out of joint,--the most so, in fact, of any joint in the body.

[Ill.u.s.tration: A BALL-AND-SOCKET JOINT

Hip joint.]

[Ill.u.s.tration: A HINGE JOINT

Knee joint, with the knee cap removed]

The hip joints are deep, strong, cup-shaped sockets upon each side of the hip bones, or _pelvis_, into which fit the heads of the _femurs_ or thigh bones. When the hip joint does become dislocated, it is very hard to put back again, on account of its depth and the heavy muscles surrounding it. It is quite subject to the attack of tuberculosis, or "hip-joint disease."

[Ill.u.s.tration: LENGTHWISE SECTION OF BONE]

The _joints_, or points at which the bones join one another, look rather complicated, but they are really as simple as the bones themselves. Each joint has practically made itself by the two bones' rubbing against each other, until finally their ends became moulded to each other, and formed the ball-and-socket, or the hinge, according to whichever the movements of the "bend" required. The ends, or heads, of the bones which form a joint are covered with a smooth, shining coating of _cartilage_, or gristle, so that they glide easily over each other.

[Ill.u.s.tration: CROSS SECTION OF BONE]

Around each joint has grown up a strong sheath of tough, fibrous tissue to hold the bones together; and, inside this, between the heads of the bones, is a very delicate little bag, or pouch, containing a few drops of smooth, slippery fluid (_synovial fluid_) to lubricate the movements of the joint. This is sometimes called the "joint oil," though it is not really oil.

Bones are covered with a tough skin, or membrane (_periosteum_). They are hardest and most solid on their surfaces, and hollow, or spongy, inside. The long bones of the limbs are hollow, and the cavity is filled with a delicate fat called _marrow_--just as an elderberry stem or willow-twig is filled with pith. This tubular shape makes them as strong as if they were solid, and much lighter.[25]

The short, square, and flattened bones of the body, such as those of the wrist, the skull, and the hips, instead of being hollow inside are spongy; and the s.p.a.ces in the bone-sponge are filled with a soft tissue called the _red marrow_ in which new red and white corpuscles for the blood are born, to take the place of those which die and go to pieces.

FOOTNOTES:

[24] You can easily prove that a bone is made up of living tissue soaked and stiffened with lime, by putting it into a jar filled with weak acid.

This will gradually dissolve and melt out the lime salts, and then you will find that the bone has lost three-fourths of its weight and that what remains of it is so soft and flexible that it can be bent, or even tied into a knot.

[25] The hollow s.p.a.ces in the bones of birds, however, are filled with air, which makes them lighter for flying.

CHAPTER XX

OUR TELEPHONE EXCHANGE AND ITS CABLES

The Brain. We are exceedingly proud of our brain and inclined to regard it as the most important part of our body. So it is, in a sense; for it is the part which, through its connecting wires, called the _nerves_, ties together all the widely separated organs and regions in our body, and helps them to work in harmony with one another. We speak of it as the master and controller of the body; but this is only partially true.

The brain is not so much the President of our Cell Republic as a great central telephone exchange, where messages from all over the body are received, sifted, and transmitted in more or less modified form, to other parts of the body. Three-fourths of the work of the brain consists in acting as "middle-man," or transmitter, of messages from one part of the body to another. In fact, the brain is far more the servant of the body than its ruler; and depends for its food supply, its protection, its health, and its very life, upon the rest of the body. The best way to keep the brain clear and vigorous is to keep the muscles of the stomach, the liver, the heart, and the entire body in good health.

What the Brain Does. The brain is the very wonderful organ with which we do what we are pleased to call our thinking, and also a number of other more important things of which we are not conscious at all. It is a large organ, weighing nearly three pounds when full grown. In shape it is like an oval loaf of bread split lengthwise by a great groove down the centre, and with a curiously wrinkled or folded surface. The two halves of the brain, called _hemispheres_ (though more nearly the shape of a coffee-bean), are alike; and each one, by some curious twist, or freak, of nature, receives messages from, and controls, the opposite half of the body--the right half controlling the left side of the body, while the left half controls the right side of the body. Thus an injury or a hemorrhage on the left side of the brain will produce paralysis of the right side, which is the side on which a stroke of paralysis most commonly occurs.

All the nerve fibres in each half or hemisphere of the upper brain run downward and inward like the sticks of a fan, to meet in a strap-like band, or stalk, which connects it with the base of the brain and the spinal cord. A very small amount of damage at this central part, or base, of the brain will produce a very large amount of paralysis. We may have large pieces of the bones of the skull driven into the outer surface of the brain, or considerable ma.s.ses of our upper brain removed, or destroyed by tumors or disease, without very serious injury. But any disease or injury which falls upon the base of the brain, where these stalks run and big nerve-knots (_ganglia_) lie, will cause very serious damage, and often death.

The whole upper brain is a department of superintendence, which has grown up from the lower brain to receive messages, compare them with each other, and with the records of previous messages which it has stored up, thus giving us the powers which we call memory, judgment, and thought. Unfortunately, however, long and carefully as we have studied the brain, we really know little about the way in which it carries out these most important processes of memory, of judgment, and of thought, or even of the particular parts of it in which each of these is carried out.

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