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reptiles, and all in common possess a spine which in its fundamental characteristics is very much the same now as when it was first evolved. In other words, the spine is a bodily structure as old as the rock-ribbed hills. It has stood the test of time, and therefore must be regarded as the most highly perfected mechanical structure in the body. Its strength combined with its flexibility and its perfect adjustment as a container for the central nervous system, makes it perhaps the most wonderful structure in the body outside of the brain and the spinal cord itself. While other organs and features of the body have been changed and modified to such an extent in the various species which have been evolved that they can hardly be recognized as having a common origin, yet the spine has remained substantially the same. It is true that the spine has been shortened in many species as the result of the loss of the tail, but this means only the dropping off of a part of it and does not greatly alter its fundamental character.

The human spine, however, differs from that of other animals in respect to its suitability for the erect posture. Man is the only animal in the world who can straighten his body and stand perfectly erect. Even the anthropoid apes when standing on their feet assume a somewhat oblique position. The vertebral column in animal life was first developed on the horizontal plane, and so, naturally, when man was evolved and adopted the erect position, certain modifications of the spine were necessary. A new strain developed on the vertebral column which was due to the new position, and so there came about certain changes in its structure. For one thing the spine became less flexible and gained in stability, especially in the lower sections. The sacrum, for instance, is created by the fusing together of several vertebrae into one bone for the sake of greater strength and stability. The sacrum in man is much broader than in animals, for it must supply solidity and strength to the lower part of the spine, thus adapting it to the vertical position, and in the same way the lower vertebrae generally are comparatively broader and heavier, gradually decreasing in size and tapering toward the top of the spine like the trunk of a tree.

This particular feature of the human backbone is worthy of special consideration because it is the upper section of the spine, in which the vertebrae are smaller and tapering, that weakness is most likely to exist. It is in this upper section of the spine that strength is most needed in order to preserve it in perfect alignment, and keep the body properly erect. And it is for this reason, as the reader will see, that exercises affecting the upper parts of the spine are most important. Therefore I have given them special attention.

The curves in the human spine are characteristic, illustrating in

another way the modification of the vertebral column that has been made necessary by the erect position. The new-born baby has a backbone that is almost straight, and in this respect it bears a strong resemblance to that of many of the lower animals. The typical human curves, however, begin to take form as soon as the child learns to sit up, and they become more marked as he learns to walk and run. These curves are essential to maintaining the balance of the body in the erect position.

There are really three curves in the human backbone, the cervical curve being convex, the dorsal concave, and the lumbar convex, when each is regarded from the forward aspect. If we consider the sacrum and coccyx, there is really a fourth curve, this being concave, although in animals generally the coccyx curves backwards and is extended to form the tail. In some of the lower animals the spine is nearly straight, while in some cases it virtually forms a complete arch from one end to the other.

These curves of the spine are generally more marked in the civilized white races than among the black and savage races, and as a rule they are more pronounced among women than among men. For instance, in comparing the sexes we find that in a woman the lumbar curve is more marked and extends slightly higher than in a man, and that the broad sacrum characteristic of the human race is even wider, being thus adapted to the broader hips and wider pelvic cavity of the child- bearing sex.

Now, the maintenance of a strong and erect spine, and especially of the normal curves of youth is most important. With the weakness of advancing age the curves, particularly in the upper part of the spine, tend to become more pronounced. The more accentuated these curves are the greater is the weakness of the spine and of the muscles of the back that is indicated. It is said that a man is as old as his spine, since the deterioration of the spine means the loss of elasticity and supporting power in the disk-like cartilages between the vertebrae, and also the loss of strength in the muscles and ligaments of the back which tend to hold the spinal vertebrae in place. It is usually found that vigorous old men who are mentally and physically active at eighty or ninety years are those who have maintained an erect bearing until late in life, who have kept their spines straight and strong instead of allowing them to bend over and double up. In other words, the deterioration of the spine means a general loss of bodily vigor and a decline in the nervous energy or vitality.

With the flattening down of the cushiony disks or cartilages between the vertebrae, and also with the dislocation even in the slightest degree of these vertebrae, there is brought about more or less interference with the free action of the spinal cord itself and of the spinal nerves. The pinching of these nerves naturally interferes with the

supply of energy to the organs controlled by them, and causes more or less serious derangement of the bodily functions. If one can keep his spine straight and strong the central nervous system will likewise be healthy and vigorous, and all organs will be supplied with a normal amount of energy and vitality.

The special exercises for the spine which I have recommended for years have the general effect not only of maintaining the proper alignment of the vertebrae and thus promoting the health and welfare of the central nervous system, but also of strongly stimulating the nervous system, and thus toning up the entire bodily organism. All movements of the spine, whether of a twisting or bending character, naturally influence the spinal cord and the spinal nerves in a mechanical way. The result is something akin to a massage of these nerve structures, and in this way, as I have long contended, it is possible directly to stimulate the source of energy and vitality. I am convinced for this reason that muscular exercise for the back is infinitely more important than for any other part of the body, important as it is for all parts. If one has only very little time each day to devote to exercise, then it would pay him best to give that time to movements which will strengthen and stimulate the spine.

The various movements that I am presenting in this chapter have been

devised