There is another portion of the body which is so intimately connected with every other, that it is placed in this chapter as also having reference to every department in the general subject of the care of health.

The body has no power to move itself, but is a collection of instruments to be used by the mind in securing various kinds of knowledge and enjoyment. The organs through which the mind thus operates are the brain and nerves. The opposite drawing (Fig. 48) represents them.

The brain lies in the skull, and is divided into the large or upper brain, marked 1, and the small or lower brain, marked 2. From the brain runs the spinal marrow through the spine or backbone. From each side of the spine the large nerves run out into innumerable smaller branches to every portion of the body. The drawing shows only some of the larger branches. Those marked 3 run to the neck and organs of the chest; those marked 4 go to the arms; those below the arms, marked 3, go to the trunk; those marked 5 go to the legs; and the lowest of all go to the pelvic organs.

The brain and nerves consist of two kinds of nervous matter - the gray, which is supposed to be the portion that originates and controls a nervous fluid which imparts power of action; and the white, which seems to conduct this fluid to every part of the body.

The brain and nervous system are divided into distinct portions, each having different offices to perform, and each acting independently of the others; as, for example, one portion is employed by the mind in thinking, and in feeling pleasurable or painful mental emotions; another in moving the muscles; while the nerves that run to the nose, ears, eyes, tongue, hands, and surface generally, are employed in seeing, hearing, smelling, tasting, and feeling all physical sensations.

The back portion of the spinal marrow and the nerves that run from it are employed in sensation, or the sense of feeling. These nerves extend over the whole body, but are largely developed in the net-work of nerves in the skin. The front portion of the spinal marrow and its branches are employed in moving those muscles in all parts of the body which are controlled by the will or choice of the mind. These are called the nerves of motion.

The nerves of sensation and nerves of motion, although they start from different portions of the spine, are united in the same sheath or cover, till they terminate in the muscles. Thus, every muscle is moved by nerves of motion; while alongside of this nerve, in the same sheath, is a nerve of sensation. All the nerves of motion and sensation are connected with those portions of the brain used when we think, feel, and choose. By this arrangement the mind knows what is wanted in all parts of the body by means of the nerves of sensation, and then it acts by means of the nerves of motion.

Fig. 48.

Fig. 48.

For example, when we feel the cold air on the skin, the nerves of sensation report to the brain, and thus to the mind, that the body is growing cold. The mind thus knows that more clothing is needed, and wills to have the eyes look for it, and the hands and feet move to get it. This is done by the nerves of sight and of motion.

Next are the nerves of involuntary motion, which move all those parts of the head, face, and body that are used in breathing, and in other operations connected with it. By these we continue to breathe when asleep, and whether we will to do so or not. There are also some of the nerves of voluntary motion that are mixed with these, which enable the mind to stop respiration, or to regulate it to a certain extent. But the mind has no power to stop it for any great length of time.

There is another large and important system of nerves called the sympathetic or ganglionic system. It consists of small masses of gray and white nervous matter, that seem to be small brains with nerves running from them. These are called ganglia, and are arranged on each side of the spine, while small nerves from the spinal marrow run into them, thus uniting the sympathetic system with the nerves of the spine. These ganglia are also distributed around in various parts of the interior of the body, especially in the intestines, and all the different ganglia are connected with each other by nerves, thus making one system. It is the ganglionic system that carries on the circulation of the blood, the action of the capillaries, lymphatics, arteries, and veins, together with the work of secretion, absorption, and most of the internal working of the body, which goes forward without any knowledge or control of the mind.

Every portion of the body has nerves of sensation coming from the spine, and also branches of the sympathetic or ganglionic system. The object of this is to form a sympathetic communication between the several parts of the body, and also to enable the mind to receive, through the brain, some general knowledge of the state of the whole system. It is owing to this that, when one portion of the body is affected, other portions sympathize. For example, if one part of the body is diseased, the stomach may so sympathize as to lose all appetite until the disease is removed.

All the operations of the nervous system are performed by the influence of the nervous fluid, which is generated in the gray portions of the brain and ganglia. Whenever a nerve is cut off from its connection with these nervous centres, its power is gone, and the part to which it ministered becomes lifeless and incapable of motion.

The brain and nerves can be overworked, and can also suffer for want of exercise, just as the muscles do. It is necessary for the perfect health of the brain and nerves that the several portions be exercised sufficiently, and that no part be exhausted by overaction. For example, the nerves of sensation may be very much exercised, and the nerves of motion have but little exercise. In this case, one will be weakened by excess of work, and the other by the want of it.

It is found by experience that the proper exercise of the nerves of motion tends to reduce any extreme susceptibility of the nerves of sensation. On the contrary, the neglect of such exercise tends to produce an excessive sensibility in the nerves of sensation.

Whenever that part of the brain which is employed in thinking, feeling, and willing, is greatly exercised by hard study, or by excessive care or emotion, the blood tends to the brain to supply it with increased nourishment, just as it flows to the muscles when they are exercised. Over-exercise of this portion of the brain causes engorgement of the blood-vessels. This is sometimes indicated by pain, or by a sense of fullness in the head; but oftener the result is a debilitating drain on the nervous system, which depends for its supply on the healthful state of the brain.

The brain has, as it were, a fountain of supply for the nervous fluid, which flows to all the nerves, and stimulates them to action. Some brains have a larger, and some a smaller fountain; so that a degree of mental activity that would entirely exhaust one, would make only a small and healthful drain upon another.

The excessive use of certain portions of the brain tends to withdraw the nervous energy from other portions; so that when one part is debilitated by excess, another fails by neglect. For example, a person may so exhaust the brainpower in the excessive use of the nerves of motion by hard work, as to leave little for any other faculty. On the other hand, the nerves of feeling and thinking may be so used as to withdraw the nervous fluid from the nerves of motion, and thus debilitate the muscles.

Some animal propensities may be indulged to such excess as to produce a constant tendency of the blood to a certain portion of the brain and to the organs connected with it, and thus cause a constant and excessive excitement, which finally becomes a disease. Sometimes a paralysis of this portion of the brain results from such an entire exhaustion of the nervous fountain and of the overworked nerves.

Thus, also, the thinking portion of the brain may be so overworked as to drain the nervous fluid from other portions, which become debilitated by the loss. And in this way, also, the overworked portion may be diseased or paralyzed by the excess.

Sometimes the intellect and feelings may be confined to one subject so exclusively as to cause mental derangement on that subject when sane in all other respects. This is called a monomania.

The necessity for the equal development of all portions of the brain by an appropriate exercise of all the faculties of mind and body, and the influence of this upon happiness, is the most important portion of this subject, and will be more directly exhibited in another chapter.

The chief causes of debility of nerves, neuralgia, sciatica, and other diseases of the nerves, are exhaustion of the nervous fountain by excess of study, or of labor, or of mental excitement of any kind. All excess of feeling, or of intellectual or physical labor, decreases the nerve centres or fountains of nervous supply. Diseases also, and often medicines, have the same effect.

When the nerves are thus weakened their minute capillaries are not able to send forward the blood, and thus become swollen or congested, and then a change in the nerve substance follows.

The remedy for this is to withdraw the blood from the congested nerves, and this is secured by exercising the muscles, thus drawing the blood from nerves to muscles. When the patient is much debilitated this exercise should be done by an operator, as in the passive exercises of the movement cure; for in such cases the nerves and brain would be still more weakened by voluntary exercise of the patient. This shows the great mistake often made by attempts to remedy weak nerves and brain that need rest, by voluntary exercise of the muscles. It also shows the mischief often done in schools where to high intellectual excitement is added vigorous gymnastic exercises.

The chief benefit of the movement cure, especially as conducted by Dr. George Taylor, of New York City, consists in various apparatus invented by him, by which various parts of the body can be exercised while the brain and nerves of the patient are at rest. By these contrivances the congested blood of the capillaries is drawn from the diseased part and all the healthful functions restored, while the patient is at rest as to any voluntary exertion of brain and nerves. When the strength will permit, voluntary exercises adapted to each case are combined with the passive movement effected by an operator:

The following are the effects of the mechanical and involuntary movements by machinery or by an operator:

They produce increased motion of particles, and so increase of absorption and nutrition.

They increase contractile power in the capillaries, and thus remedy congestion.

They direct nervous energy to defective parts and remove obstructions.

They increase respiration, and thus increase the life-giving oxygen and animal heat, while they repress excess in other congested parts.

They increase nutrition, and also the secretion and discharge of morbid matter from diseased or weakened parts.