2. The power of healing which is evidenced either by what is termed "healing by first intention", or "healing by second intention", upon the occurrence of any wound or abrasion. Whether the continuity of the tissues has been broken either by bursting of an abscess or by a clean cut, the process of repair is always the same. The wound is filled with new connective tissue, its surface is covered by the proliferation of the surrounding epithelium, the nervous and circulatory Channels are reestablished and the wound healed. Clean cuts, on healthy individuals heal with a minimum' amount of connective tissue so that the results are scarcely apparent to the naked eye. This is called "healing by first intention" or "primary union."

"Healing by second intention" does not differ in any great respect from "healing by first intention." There is, however, an obvious formation of granulation tissue and the formation of a superficial scar. The same formation of granulation tissue (embryonic connective tissue), coagulation, fibrin formation and proliferation of capillaries and connective tissue take place in both forms of healing. Both are accompanied by more or less of inflammation with the destruction of some tissue. Bone and nerve tissue are the best regenerators, although there is more or less regeneration in other tissues.

Let us consider the natural healing of a wound, scratch or broken skin. We have become so accustomed to this familiar phenomenon that we have come to regard it as an almost mechanical process. But a close examination of the process shows us the presence of that same marvelous "intelligence" that builded the body from a tiny microscopic speck of protoplasm to its present state.

Whenever the skin, and maybe the deeper tissues, is broken or cut, there is an exudation of blood which coagulates and forms an airtight scab. This scab serves as a protection to the wound, and remains for a shorter or longer time as needed. Underneath this scab a wonderful thing occurs. Blood is rushed to the injured part in large quantities. The tissues, nerve and muscle cells, etc., on each side of the wound start multiplying rapidly, and build a "cell-bridge" across the gap until the severed edges of the wound are reunited. But this is no mere haphazard process. Everywhere is apparent the presence of directing law and order. The newly formed cells of the blood vessels unite with their brothers on the other side so that in an orderly and evenly manner the channels of circulation are re-established. In this same lawful and orderly manner the connective tissues reunite. Skillfully, and just as a lineman repairs a telegraph system, do the nerve cells repair their broken line. Muscles and other tissues are repaired in a similar manner. And what is a wonderfully marvelous fact to observe, no mistakes are made in this connecting process--muscles do not connect with nerve or blood vessels, or with connective tissue, but each tissue connects with its kind.

Experiments have shown that if, in the repair of wounds, one factor of repair is interfered with, this is compensated by acceleration of others. If one regenerating mechanism fails it is replaced by another. After a hemorrhage, two converging mechanisms re-establish arterial pressure and blood volume. The arteries contract on the one hand and liquid is brought from the tissues and digestive tract on the other. If either of these mechanisms fails, the other is capable of compensating the failure. The body is thus seen to have more than one means of accomplishing the same adjustment, so that the result alone and not the procedure is invariable.

After the wound is healed, when a new skin has been formed, so that there is no longer any need for the protecting scab, nature proceeds to undermine and get rid of it. As long as the scab was useful it was firmly attached to the skin so that it was not easy to pull off, but when there was no longer need for it, it was undermined so that it fell off of its own weight.

If heat or friction is applied to the skin of sufficient intensity and duration a blister forms. That is, a watery exudate or serum is poured out of the surrounding tissues and circulation into the "space" between the dermis and epidermis and detaches the dermis from this, raising it up and thus protecting the tissues beneath. The accumulated fluid holds back the heat or, in the case of sun burn, the actinic rays, and protects from the friction. This little piece of engineering work is quite obviously a defensive work. In both burns, and sunburn, inflammation and healing follow the blister and, in the case of sun-burn, pigmentation to protect from future sun-burn.

We get, if possible, a still more wonderful view of how nature performs her work, if we observe the healing of a fractured or broken bone. If a limb is broken so that the sharp ends of the fractured bone tear the muscles and blood vessels, the break is speedily surrounded by a bloody clot of fibrin and by osseous and muscular debris. Circulation increases and the limb swells. The blood brings to the wounded section the nutritive substances necessary for the regeneration of tissue. In and around the fracture all structural and functional processes are directed toward repair. In order to accomplish this, tissues become what they need to be. As an example, a shred of muscle near the fracture metamorphoses into cartilage. A liquid substance is secreted and deposited over the entire surface of the bone in each direction from the point of fracture. This secretion quickly hardens into a bone-like substance and is firmly attached to the two sections of the bone. Until nature can repair the damage this "bone ring" forms the chief support whereby the limb can be used. By the same process of cell multiplication which we saw in the healing of the wound, the ends of the bone are reunited. Cartilage, which forms to temporarily unite the broken ends of the bone, is later transformed into bone, so that the bone is regenerated in the same way it was built up during embryonic life. The circulatory channels are re-established through the part. It is then that the "bone ring" support is softened and absorbed, except about an eighth- to a quarter of an inch about the point of fracture.

During the few weeks required to repair a broken bone, an immense number of chemical, nervous, circulatory, and structural changes, correlations, and adjustments are instituted and carried out. They are all directed to and concentrated upon the work of repair. The physiological processes of regeneration are set in motion by the flow of blood from the vessels at the time of the accident, by the accompanying pain, and by the juices from the bone marrow and lacerated muscles. Each phenomenon results from the preceding one.

You strike your finger with a hammer. A very painful bruise is the result. There is an effusion of blood under the surface, with inflammation and discoloration. The tissues are mangled, the cells are broken, and many of them are killed. But the thumb does not remain in this condition. As time passes, new tissues are formed to replace the dead ones, the dead cells and the dark, wasted blood are absorbed and carried away. The inflammation subsides, the pain ceases, the bruise is cured, and soon forgotten. Thus again is manifested the marvelous intelligence of the power that superintends the workshop, which we call our body. Once, again, we watch his work and see his marvelous efficiency as a workman.