Two human tissues are essentially non-vascular, the cornea and cartilage. The former appears to be nourished by cellular interspaces which may admit leukocytes from the surrounding tissues, and through these proliferation and vascularization occur; while a scar in the cornea remains permanent, and the new tissue by which repair is brought about never becomes transparent like the cells composing the cornea proper. In cartilage scar tissue is produced, as in other tissues, by a similar process, in spite of the extent of the cartilaginous layer and its non-vascularity. In general the more specialized a tissue the less completely does it heal, and the specialized tissues, like the retina, etc., seem to be incapable of reproducing themselves. Low down in the animal scale some parts can be more or less reproduced. In the ascending forms there is less tendency in this direction; in man there is little reproduction of an original tissue, scar tissue taking the place of most of that which has been lost. An apparent exception to this is seen in the osseous system, where a large amount of bone may often be reproduced. Epithelium, also, whether on the external or internal surfaces of the body, can regenerate itself in large degree and amount. From every small island or mass of epithelial cells which can be retained new cells may thus be reproduced; hence accrues the advantage of leaving such epithelial collections whenever possible, and wherever they may be beneficial. If upon a burnt area it happens that epithelium has not been completely destroyed, new skin may be confidently looked for from each clump of epidermal cells. It should be remembered, however, that with the epidermization of a surface under these circumstances merely an epithelial covering is secured. The distinctively dermal appendages, such as hair, sweat glands, and sebaceous glands, are not reproduced. If the highest ideal results are to be secured in any case the parts must be put in the most favorable condition, which means early surgical attention to every wound.
INJURIES TO VESSELS.
Bloodvessels are subject to contusion, to laceration, and to incision. They may be contused by superficial blows, compressed against underlying bone, torn in the replacement of old dislocations, or punctured or incised by accidental or homicidal injuries. A vessel which is not abruptly divided but is seriously injured will usually sustain a separation of its internal and middle coats, which curl up within the external coat, occlude the channel, and lead to thrombosis. A vessel thus occluded may tend to gangrene of the parts supplied by it or to a temporary ischemia, with numbness and pallor if an artery, or to passive edema if a vein. In cases of such injury it is always hoped that the blood supply will be provided through the collateral circulation. If a vessel be torn or cut across there may result a hematoma which may lead to immediate prostration, from hemorrhage, and to gangrene by stopping the blood supply. Such blood tumor rarely pulsates, but may cause extreme pain. The character and the size of the swelling will depend upon the tissues which surround the injured vessel. Cessation of the pulse on the distal side of an injury nearly always implies temporary occlusion. Traumatic aneurysm may be produced by lateral injury to an arterial trunk, by which its continuity as such is yet not completely disrupted.
If a large outpour of blood has occurred it will be safer to incise and turn out the clot and secure the injured vessel. In milder cases the surgeon should do all that he can by rest and by position to favor restoration of blood circulation. After the subsidence of acute symptoms massage and gentle motion will serve to promote absorption of the escaped blood. Cases will occasionally occur in which the principal arterial trunk of a limb should be tied, hoping thereby to save the member. Amputation may be the last resort when gangrene is impending.
Injury to the veins is of a less serious nature in so far as immediate consequences are concerned; nevertheless a punctured wound or a large vein is always a serious matter. The pressure of the blood may produce gangrene, or cause so large a hematoma that it should be incised.
Fine silk sutures may be applied to wounded vessels, arteries or veins, when they have been partially severed.
The healing process in all these cases is essentially the same. It may mean the formation of a clot in or around a vessel, followed by absorption of its principal portion and organization of what remains. A vessel itself which has once been occluded by thrombus will usually remain closed, a cord of fibrous tissue taking its place. Only in rare instances is continuity of the blood channel preserved or regained. In such cases the collateral circulation affords the life-saving feature. The granulations which intrude themselves into the clot gradually substitute tissue for coagulum, the conversion beginning promptly, but often occupying weeks for its completion.
Lymph vessels may be lacerated in almost any injuries and more or less lymph escape with the blood. When the skin is torn from the underlying parts lymph collects in the cavity thus made, while its wall may undergo more or less organization, and formation of a lymph cyst results. Should one of these connect with a good-sized lymph duct, as, for instance, in the neck the thoracic duct, then lymph cysts of considerable size might form. Should these rupture or be opened lymph fistulæ might result.
INJURIES OF NERVES.
By small hemorrhages into a nerve sheath nerve function may be either temporarily or permanently disturbed. A compression too long-continued may lead to degeneration within the nerve fibers. Providing this do not occur there may be complete restoration of function, or there may result chronic neuritis, with pain and irritation. A later consequence of all nerve injuries is more or less serious disturbance of sensation, while still later parts supplied by the affected nerves may undergo more or less atrophy as well as spastic contraction, by which loss of function and deformity are produced.