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SKIN DISEASES

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Originally appearing in Volume V25, Page 192 of the 1911 Encyclopedia Britannica.
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SKIN DISEASES . The diseases of the skin do not essentially differ from those of the other See also:

organs of the See also:body. Like these, the skin is composed of cells resting on a connective See also:tissue framework, in which run the vessels which nourish it and the nerves which keep up its communications with the See also:rest of the body. But it has certain See also:differences from other organs, some dependent on its structure and some on its exposed position. Thus, instead of, like the See also:kidney, to which it may best be compared, having its epithelium faced by epithelium, all lies open, and the various processes are all " one-sided." There are no depths to be attacked, and any diseases, if they spread, must do so superficially; spreading as they often do equally in all directions, the diseases of the skin have a tendency to' assume a circular See also:form, independently of any parasitic cause, though when such cause is See also:present the patches are of a more perfectly circular shape. Further, from the extent of its superficial See also:area and its exposed position, the skin is liable to be attacked by more forms of irritation, parasitic or other, than any other See also:organ of the body. Every See also:stage and variety of disease is open to view; See also:minute differences, See also: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 See also:eye, can the changes be watched from See also:day to day; in none can so many stages of the same disease be simultaneously observed; and in no other is it so See also:simple a See also:matter to remove and instantly See also:fix for microscopic examination the living tissue. The multitude of its affections renders the difficulties of arranging the diseases of the skin very See also:great, and the See also:absence of any generally accepted See also:scheme of See also:classification has always been and still remains one of the See also:main obstacles to their intelligent study. The older systems, constructed before the days of See also: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 See also:gross parasites as the See also:Acarus scabiei (the itch See also:mite), the pediculi (lice), and the hyphomycetic See also: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 See also:nerve See also:influence by another, while a third assumes an agnostic position.

The following is a useful working classification. I. THE DERMATONEUROSES.—(a) Sensory: See also:

anaesthesia, hyperaesthesia, See also:pruritus; (b) vaso-motor: urticaria, erythema multiforme, angio-neurotic oedema, See also:pellagra, See also:purpura, certain forms of See also:eczema, erythema pernio (See also:chilblains), erythema nodosum, See also:herpes, cheiropompholyx, alterations of pigment; (c) trophic: sclerodermia, perforating See also:ulcer, See also:Charcot's See also:bed-sore, the lesions of certain forms of leprosy, Raynaud's disease, See also:Morvan's disease, See also:pemphigus, See also: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 See also:heat; the sebaceous glands, rosacea, See also:seborrhoea; the See also:hair follicles, alopecia, greyness. 2. See also:LOCAL INOCULABLE DIsEASEs.—The agents producing these are parasitic in origin and may be divided into those caused by See also:animal parasites, See also:vegetable parasites and various micro-organisms. (a) Animal parasites: See also:scabies, due to the Acarus scabiei or itch mite; See also:pediculosis, See also:guinea-See also:worm disease, due to the Dracunculus medinensis; trichinosis, due to the cysticercus cellulosae; See also:elephantiasis, due to the filaria sanguinis hominis; various eruptions produced by accidental parasites such as the See also:harvest See also:bug (leptus autumnalis), the jigger or See also:sand See also:flea (Dermatophilus penetrans), met with in the tropics. (b) Vegetable parasites: See also:ringworm, caused by the Trichophyton tonsurans; See also:favus, caused by the Achorion Schonleinii; Linea versicolor, caused by the Microsporon Furfur; erythrasma, due to the Microsporon minutissimum; See also:actinomycosis, due to the Actinomyces or See also:ray fungi; mycetoma or See also:Madura See also:foot, due to Dyscomyces; aspergillosis and See also:pinto, caused by an unknown fungus; streptothrix infections other than from the ray fungus, sporotrichosis; blastomycetic dermatitis, due to a fungus of the yeast See also:family. ' (c) Micro-organisms: impetigo contagiosa, caused by inoculation with streptococci; furunculosis or boils, due to the staphylococcus pyogenes aureus and albus; See also:carbuncle, a deeper infection also caused by staphylococci; See also:anthrax, caused by the bacillus anthracis; sycosis, due to a staphylococcic infection of the hairy parts; See also:acne, due to a bacillus called by Gilchrist the bacillus acnes, thought to be identical with the micro-organism of Sabouraud and See also:Unna; furunculosis orientalis (See also:Delhi See also:boil, See also:Aleppo boil, See also:Biskra See also:button), a tropical disease in which the See also:parasite is not yet identified; certain forms of eczema, notably the pustular forms. 3. See also:GENERAL INOCULABLE DISEASES.—See also:Tuberculosis, manifesting itself as lupus vulgaris, verruca necrogenica, erythema induratum or as tuberculous ulcerations. In all these See also:Koch's bacillus has been identified. Syphilis, caused by the Spirochaeta pallida of Schaudinn and Hoff See also:mann, in which there are See also:primary, secondary and See also:tertiary skin lesions.

Leprosy due to the bacillus lepra. See also:

Yaws (framboesia), caused by a specific parasite, the Spirochaeta pertenius. See also:Glanders, due to inoculation with the bacillus mallei. Added to these are See also:erysipelas and the various exanthematous fevers. 4. DISEASES OF UNCERTAIN See also:AETIOLOGY.—See also:PSOriasis, pityriasis rubra, pityriasis rosea. 5. ERUPTIONS DUE TO DRuGs.—These may follow on the See also:internal See also:administration of See also:chloral See also:belladonna, See also:copaiba, phenazone, See also:mercury, See also:quinine, See also:tar, See also:stramonium, See also:sulphonal, salicylic See also:acid and the salicylates and bromides. 6. NEW GROWTHS.—Benign: cheloid and fibroma, See also:naevus pigmentosus, vascular naevi, telangiectasis, lyniphangioma, myoma, mycosis fungoides, papilloma, adenoma, moluscum contageosum, rhinoscleroma,cysts and warts (including corns and horny growths). See also:Malignant: sarcoma, carcinoma, rodent ulcer, See also: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 See also:special structure of the skin such as See also:hypertrophy and See also:atrophy, disorders of the sweat glands and sebaceous glands and alterations of pigment.

Some of the See also:

groups of diseases classed as the dermatoneuroses are manifestations of widely different diseases; thus anaesthesia and hyperaesthesia occur in See also:hysteria; while the acute bed-sore of Charcot (a form of local See also:gangrene) and perforating ulcer are generally due to an inflammatory See also:condition of the nerve trunks. In the See also:group of diseases known as purpura, where haemorrhages of varying See also:size make their See also:appearance on different parts of the skin, the See also:lesion is considered to be due to a toxin or autotoxin acting directly on the vascular walls. In some cases we know it to be inorganic, such as See also:phosphorus or mercury, in others organic as smallpox, See also:measles, typhus or tuberculosis; or the haemorrhages may occur in connexion with new growths such as sarcoma and lymphadenoma. Why these very different causes should combine to produce the phenomenon of See also:haemorrhage is not clear. The disease known as urticaria or See also:nettle-rash is probably due to some irritant See also:poison circulating in the See also:blood, but the causes producing it vary from constitutional diseases such as See also:gout and See also:malaria to certain articles of See also:diet which See also:act as gastro-intestinal irritants such as pork and See also:shell-See also:fish. It has been known also to follow on See also: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 See also:pathology of the lesions in this disease is as follows: reacting to some irritant, the blood-vessels dilate, serum is poured out from them into the tissues around, and compressing the vessels from without empties them of blood. This explains the See also:white centre of the urticarial weal, the red margin of which is the clinical expression of the dilated and uncompressed vessels at the border. In those diseases grouped together under the name of erythema, although the See also:majority of authors See also:place them under the heading of inflammation, there is 'a See also:good See also:deal suggestive of a See also:close relation to urticaria. Some cases are caused by the ingestion of certain drugs, a good many are directly associated with the rheumatic poison, while others are apparently connected with fermentative changes in the gastrointestinal See also:tract. Thus all those examples of the disease with the cause of which we are approximately acquainted are readily enough attributed to some circulating irritant. This disease differs histologically from urticaria in the persistent See also:dilatation of the vessels.

Although serum is poured out from them as freely as in urticaria, the dilatation of the vessels is so active that they are not compressed as in that disease, while the presence of numerous cells around the vessels seems to suggest a more severe irritant, and the fact that the lesions are clinically more persistent further confirms that See also:

suggestion. When certain irritants are applied to the skin we know before-See also:hand what effects they will produce. Thus croton oil produces a vesicular and pustular eruption, that of See also:cantharides is vesicular or bulbous, while other drugs are followed by results dependent on their concentration, ranging from a See also:mere redness produced by dilute applications to actual See also: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 them—it 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 See also:surface. The See also:epithelial cells are, immediately if the irritation be slight, later if it be more severe, stimulated to increased activity of growth and See also:production; and this activity, often misdirected, is so great that the normal See also: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 See also: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 reaction—which is presumably largely dependent on the irritant to which it is due—we have various degrees and forms of inflammation of the skin, all of them covered clinically by the See also: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 See also: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 See also:advantage of de-finitely knowing their cause.

Thus in impetigo contagiosa we know, mainly owing to the See also:

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 See also:common name of ringworm, a reaction more resembling that of eczema is produced. There is the same dilatation of the See also: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 See also:early becomes purulent (this is said to occur regularly when the disease is contracted from the See also: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 characters requiring See also:notice here.

Keloid is a See also:

peculiar form of fibroma which, although benignant as regards any general infection, invariably recurs locally after removal. Rodent ulcer is a form of See also:cancer which occurs usually on the See also:face, and whose malignancy is almost entirely local. The class of atrophies of the skin comprises those diseases where the atrophy is primary, and those where it succeeds to previous hypertrophic or inflammatory changes. Anomalies of pigmentation are those of excess and lack. Chloasma, in which dark patches appear, most frequently on the face, is usually associated with disease of some internal organ, such as the See also: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 See also: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, See also:drug rashes and the eruptions of tlon. specific fevers, while others, such as herpes zoster, See also: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 See also:outer See also:side of the elbows and knees. In certain diseases of See also: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 See also:nose or See also:orbit.

The face too is usually the selective site of lupus vulgaris. The See also:

scalp is the See also:chief site of two varieties of lesion—the pustular, as in pustular eczema and impetigo contagiosa, or the dry and scaly eruptions, as psoriasis, ringworm and squamous syphilides. The genital organs are the seat of vesicular eruptions such as herpes or eczema or occasionally scabies; they are also the seat of ulcers, chiefly venereal, and of secondary syphilides. Scabies or itch tends to occur on the hands, and the characteristic burrows are noticeable between the fingers. The hands too are subject to various forms of eruption known as See also:trade eruptions, due to the handling of See also:paraffin, tar, See also:sugar, See also:salt, See also:lime, See also:sulphur, &c. The lesions mostly simulate eczema, and are frequent amongst tanners, dyers, chemists, bakers and washer-See also:women, and workers in the electro-plating trade. Exposure to the X-rays sets up a form of dermatitis, either an acute erythematous form due to a single prolonged exposure or a chronic form affecting operators who have been exposed over prolonged periods. Ulceration and considerable destruction of the epidermis may take place together with the occurrence of warty growths which tend to become epitheliomatous. For an See also:account of the treatment of the best known skin diseases see under their See also:separate headings.

End of Article: SKIN DISEASES

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