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Encyclopedia Britannica - Main :: SIV-SOU |
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SKIN DISEASES . The diseases of the skin do not essentially differ from those of the other organs of the body
tissue framework, in which run the vessels which nourish it and the nerves which keep up its communications with the rest of the body
of irritation, parasitic or other, than any other organ of the body. Every stage and variety of disease is open to view; minute differences, minor or important, are at once noted; and thus it is that the recognized distinct maladies of the skin are so numerous. In no other organ, with the partial exception of the eye, can the changes be watched from day to day; in none can so many stages of the same disease be simultaneously observed; and in no other is it so simple a matter to remove and instantly fix for microscopic examination the living tissue .The multitude of its affections renders the difficulties of arranging the diseases of the skin very great, and the absence of any generally accepted scheme of classification has always been and still remains one of the main obstacles to their intelligent study. The older systems, constructed before the days of bacteriology, were commonly based on the form which the eruption assumed (scaly, moist, purulent), but they usually contained in addition a certain number of diseases under the heading of Parasitic. Though obviously illogical, such systems served well enough while the recognized parasitic diseases were few, such as those caused by such gross parasites as the Acarus scabiei (the itch mite), the pediculi (lice), and the hyphomycetic fungi such as the Achorion Schonleinii. The discoveries of bacteriology have enormously enlarged this class, but the difficulty is that one and the same disease is regarded as parasitic by one authority, as dependent on nerve influence by another, while a third assumes an agnostic position.The following is a useful working classification. I. THE DERMATONEUROSES.(a) Sensory: anaesthesia, hyperaesthesia, pruritus; (b) vaso-motor: urticaria, erythema multiforme, angio-neurotic oedema, pellagra, purpura, certain forms of eczema, erythema pernio (chilblains), erythema nodosum, herpes, cheiropompholyx, alterations of pigment; (c) trophic: sclerodermia, perforating ulcer, Charcot's bed-sore, the lesions of certain forms of leprosy, Raynaud's disease, Morvan's disease, pemphigus, lupus erythematosus, the skin lesions of syringomyelia; (d) glandular, according to the gland affected,as the sweat-glands, hyperidrosis, haematidrosis, bromidrosis, miliaria papulosa, or prickly heat; the sebaceous glands, rosacea, seborrhoea; the hair follicles, alopecia, greyness. 2. LOCAL INOCULABLE DIsEASEs.The agents producing these are parasitic in origin and may be divided into those caused by animal parasites, vegetable parasites and various micro-organisms. (a) Animal parasites: scabies, due to the Acarus scabiei or itch mite; pediculosis, guinea-worm disease, due to the Dracunculus medinensis; trichinosis, due to the cysticercus cellulosae; elephantiasis
3. GENERAL INOCULABLE DISEASES.Tuberculosis, manifesting itself as lupus vulgaris, verruca necrogenica, erythema induratum or as tuberculous ulcerations. In all these Koch's bacillus has been identified. Syphilis, caused by the Spirochaeta pallida of Schaudinn and Hoff mann, in which there are primary, secondary and tertiary skin lesions. Leprosy due to the bacillus lepra. Yaws (framboesia), caused by a specific parasite, the Spirochaeta pertenius. Glanders, due to inoculation with the bacillus mallei. Added to these are erysipelas and the various exanthematous fevers. 4. DISEASES OF UNCERTAIN AETIOLOGY.PSOriasis, pityriasis rubra, pityriasis rosea. 5. ERUPTIONS DUE TO DRuGs.These may follow on the internal administration of chloral belladonna, copaiba, phenazone, mercury, quinine, tar, stramonium, sulphonal, salicylic acid and the salicylates and bromides. 6. NEW GROWTHS.Benign: cheloid and fibroma, naevus pigmentosus, vascular naevi, telangiectasis, lyniphangioma, myoma, mycosis fungoides, papilloma, adenoma, moluscum contageosum, rhinoscleroma,cysts and warts (including corns and horny growths). Malignant : sarcoma, carcinoma, rodent ulcer, Paget's disease.The skin is liable to the same pathological conditions as other structures of the body, such as changes in vascularity, inflammations, invasion by parasites and new growths together with changes due to the special
haemorrhage is not clear.The disease known as urticaria or nettle-rash is probably due to some irritant poison circulating in the blood, but the causes producing it vary from constitutional diseases such as gout and malaria to certain articles of diet which act as gastro-intestinal irritants such as pork and shell-fish. It has been known also to follow on mental emotion and is said to be frequent in the neurotic diathesis, but an attack may be set up by any local irritant such as stings or bites. The pathology
When certain irritants are applied to the skin we know before-hand what effects they will produce. Thus croton oil produces a vesicular and pustular eruption, that of cantharides is vesicular or bulbous, while other drugs are followed by results dependent on their concentration, ranging from a mere redness produced by dilute applications to actual death of' the skin from concentrated ones. With the milder irritants which produce the results clinically known as eczema we have invariably more or less pronounced certain definite phenomena. The blood-vessels dilate; serum is exuded from themit may be merely into the deeper layers of the skin, or it may reach into and among the epidermic cells, or burst its way through these and appear in drops on the surface. The epithelial cells are, immediately if the irritation be slight, later if it be more severe, stimulated to increased activity of growth and production; and this activity, often misdirected, is so great that the normal process of hardening in the cells is interfered with, and we have what is known as parakeratosis (irregular cornification) and the consequent production of scales. Should this be the prominent pathological change, the exudation spends itself among the cells of the scales, and a condition pathologically moist appears to the clinical observer as a dry eruption. Thus according to the reactionwhich is presumably largely dependent on the irritant to which it is duewe have various degrees and forms of inflammation of the skin, all of them covered clinically by the term eczema. When such a dermatitis is produced experimentally by the application of such an irritant as croton oil we can more or less accurately predict the duration of the inflammation, which gradually becomes less and less and usually terminates in dry scaling. So in eczema, as long as'the irritant continues to act, so long will its results be evident on the skin. Unfortunately the irritant which is the cause of eczema is still a matter of dispute. In studying other inflammations we have the advantage of de-finitely knowing their cause. Thus in impetigo contagiosa we know, mainly owing to the work of Saboraud, that the cause of the disease is the streptococcus pyogenes. The first result of inoculation is a minute red spot (dilatation of the vessels), which is rapidly followed by the appearance on the surface of a vesicle or bleb (exudation of serum), which is soon converted into a pustule, the whole dries up into a scab, which when thrown off discloses a healthy or slightly reddened skin. Fresh areas may be constantly attacked. In ringworm, where the cause of the disease is the growth in the superficial layers of the skin of one or other of the different varieties of fungus grouped together under the common name of ringworm, a reaction more resembling that of eczema is produced. There is the same dilatation of the vessel with exudation of fluid, sometimes reaching the surface in the form of vesicles, sometimes spending itself through and among the epidermic cells and only evidenced clinically by the presence of more or less scaling. In other cases the exudation early becomes purulent (this is said to occur regularly when the disease is contracted from the horse), a change which, though occasionally noted, is by no means frequent in eczema. The inflammations of the corium or deeper layer of the skin are due, with very few exceptions, to the growth of well-known organ-isms. Erysipelas, furuncle, anthrax and glanders are diseases which run an acute course and rapidly terminate, the two former usually in recovery, the two latter often fatally. The other more chronic affections all follow one course; in their earlier stages there is a new growth of connective tissue cells in their lowest forms (granuloma), and this later breaks down, either rapidly, as in syphilis, or slowly, as in tuberculosis and leprosy. Most of these diseases leave behind them a well-defined scar. The new growths of the skin are the same as those found else-where. Only two present special
liver or uterus, being frequently observed in pregnancy. The cause of vitiligo, in which the pigment normally present disappears from certain areas, a phenomenon more striking in coloured than in white races, is unknown.Diseases of the skin tend to manifest themselves in certain parts of the body; i.e. certain diseases exert a selective influence on the Selective sites of their eruption. Symmetry is characteristic of distAbu= eczema, psoriasis, drug rashes and the eruptions of tlon. specific fevers, while others, such as herpes zoster, ring- worm, tertiary syphilis and new growths, tend to be asymmetrical. Eczema selects the flexor aspect of the limbs and the neighbourhood of folds of skin and opposed surfaces, while psoriasis favours the extensor surfaces and the outer side of the elbows and knees. In certain diseases of nervous origin, notably in herpes zoster, the eruption follows the course of a certain nerve. In the face we get erythema, lupus erythematosus, rosacea, eczema, actinomycosis, &c., and syphilitic and malignant ulcers. Rodent ulcer usually selects the face, and generally the nose or orbit. The face too is usually the selective site of lupus vulgaris. The scalp is the chief
For an account of the treatment of the best known skin diseases see under their separate headings. End of Article: SKIN DISEASES If you wish, you can link directly to this article.
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