DISEASES OF THE SKIN.

ELEMENTARY LESIONS.

Before describing the diseases of the skin it is necessary to mention the various changes taking place in its structure, which constitute the elementary lesions common to several different diseases. The older classification of Willan and Bateman was based upon those lesions: there was a group of vesicular diseases, one of scaly diseases, one of papular diseases, and so on. But it is now seen that such a classification brings together diseases that have no special connection; and, on the other hand, there are many diseases which produce at the same time, or successively, two or three different elementary lesions, and would be, therefore, put into as many different classes. Hyperæmia. This consists of redness, of varying extent, due to the blood-vessels being distended with blood. It may be (1) an active hyperæmia from vasomotor paralysis; (2) an early inflammatory hyperæmia, with slight swelling, tenderness, and some indications of pyrexia; or (3) a venous hyperæmia, or passive congestion, with a more blue or livid color than in the other forms. In all cases the redness disappears on pressure, to return when the pressure is removed quickly in the two first cases, slowly in the last.

Hemorrhages.-Cutaneous hemorrhages form larger or smaller spots, of bright red, dark red or purple color: they do not disappear on pressure; the blood is gradually absorbed, and the color fades into brown or brownishyellow, or goes through several changes, becoming successively brown, green, and yellow, in the larger subcutaneous hemorrhages. A yellowishbrown stain may be left for a long time. The smaller spots are called petechia, the larger ecchymoses: if they form streaks they are called vibices. In capillary ecchymosis a very fine mottling is produced, which looks like a hyperæmia, until it is found to persist under pressure.

Papules or Pimples.-Small red or pink elevations of the skin, solid, or at least not visibly containing fluid. They arise mostly in the cutis, but may be imitated by accumulations of epidermic scales.

Vesicles or Vesicula.-Small blisters (from 1 to 3 mm. in diameter), due to the accumulation of more or less clear fluid under the upper layers of the epidermis. They are frequently inflammatory, seated upon an inflamed base, and contain a yellow albuminous serum.

Blebs or Bullæ.-Larger vesicles, from 5 mm. to an inch or more in

diameter. The fluid contents are clear, or slightly turbid, or blood-stained. They are often situate on an inflamed base: they heal by discharge of their contents, and the drying and shedding of the epidermic scale.

Pustules or Pustulæ.-Vesicles or bullæ containing pus.

Scabs or Crusts.-Irregular flat masses of dried serum, pus, or blood, or mixture of these materials, forming upon and adherent to the raw surface which has secreted them, and frequently the result of a vesicle, pustule, or bulla.

Wheals or Pomphi.-A circumscribed oedema of the corium, producing a pale pink or white elevation of the skin.

Scales or Squamæ.-Collections of epidermic cells in the form of flakes. Sometimes, as in seborrhoea, there is a large admixture of the fatty matter of sebum. Scales vary from the small branny particles of measles (furfuraceous) to the large exfoliations of pityriasis rubra, and some cases of scarlatina, or the thick adherent masses of psoriasis.

Scratch Marks.-Linear lesions of the skin, from a third to two inches in length, produced by the nails, and bearing small crusts of blood. mately, if deep enough, they become linear or fusiform cicatrices. Their direction generally bears a definite relation to the position of one or both hands, and parts of the body which the hands cannot reach are exempt from them.

Raw or Excoriation.-A patch of skin deprived of the upper layer of the epidermis, and exposing the rete Malpighi. It is of a vivid red color, tender to the touch, and secretes a small amount of serum, which may dry into a crust.

Chaps, Rhagades, or Rimæ.-Cracks or fissures through the epidermis, reaching the rete Malpighi or corium beneath, very sore, and apt to bleed.

Sore or Ulcer.-A loss of substance involving the epidermis, and extending to the papillary layer. The base is covered with granulations, and secretes pus.

Scar or Cicatrix.-The new growth of connective tissue, which results from the healing of sores, involving the papillary layer and deeper corium. When recent they are pink or bluish in color. Finally they become dead white, and contract in size.

Nodules. Solid elevations larger than papules. They have been called tubercles-a name which is now best limited to the specific lesion which causes phthisis.

Stains or Macula.-Patches of skin more deeply pigmented than normal. They may arise from a preceding hyperæmia, and then disappear shortly. They are generally more permanent if arising independently.

CLASSIFICATION.

The diseases of the skin will be described in the following order :

Inflammatory conditions or forms of dermatitis.

Hypertrophies.

Atrophic conditions.

Alterations of pigment.

New growths.

Diseases of the sweat glands.

Diseases of the sebaceous glands.

Diseases of the hair and hair follicles.

Vegetable parasites.

Animal parasites.

All that need be said of hemorrhage into the skin is contained in the chapter upon Purpura. Syphilitic skin diseases have been described under Syphilis.

INFLAMMATORY CONDITIONS, OR FORMS OF
DERMATITIS.

ERYTHEMA.

Erythema (from èpúɑŋua, a blush) has a rather wide signification. A redness of the skin may be set up by external irritants, or form a part of the infectious diseases called exanthemata, and to these the name has been applied. In both these cases, however, there is an early phase of inflammation. Another class has been called by Hebra Erythema exudativum, and is characterized by much more definite and pronounced inflammatory lesions. The skin is red, swollen, and tender. In some cases bullæ or vesicles are formed; and blood may be effused into them or into the corium. Other cases may be considered as intermediate, in which there is certainly more than mere hyperæmia; but the inflammatory exudation is not considerable. It will be best to consider, first, the more marked conditions known as Erythema exudativum, which includes E. multiforme, E. iris, and E. nodosum.

ERYTHEMA MULTIFORME.

As the name suggests, there is very great variety in the lesions produced. In all cases they are bright or dark-red elevations of the skin, which may be in the form of papules (E. papulatum), or in larger patches or nodules, the size of a sixpence or a shilling piece. Such a patch may clear at the centre, and leave a ring (E. annulatum); if this enlarges it may coalesce with neighboring rings and produce sinuous or scalloped patches (E. gyratum). Erythema marginatum has a similar outline: the peripheral margin.

of the red band forming the ring is raised abruptly, and the central margin gradually slopes toward the skin. Sometimes a ring of erythema is surrounded by another ring outside it, and this by another further out, while the first ring is beginning to fade. I have seen four such rings at the same time.

Occasionally bullæ or vesicles appear on these patches, and sometimes petechiæ or ecchymoses may occupy the centre of a broad papule. The raised patches last a few days and then gradually subside, often leaving a brown or brownish-yellow stain, even if there has been no obvious hemorrhage into the structure of the skin. The whole duration is from two to four or six weeks. It may begin with some malaise, it is occasionally accompanied by not very definite joint pains; and it is a not infrequent occurrence to have an eruption of erythema, especially E. marginatum, and hemorrhagic forms in the course of ordinary acute rheumatism. The hemorrhagic forms are called Peliosis rheumatica, but hemorrhages (purpura) certainly occur also in rheumatism without any preceding true erythema.

Erythema multiforme occurs especially on the back of the hand and forearm, the front of the leg, and the dorsum of the foot; and on the face, neck, front of the chest, and abdomen.

ERYTHEMA IRIS ERYTHEMA BULLOSUM-HERPES IRIS.

This appears to be an erythema with the formation of vesicle or bulla as a result. It is comparatively uncommon. Two varieties are described. In the first, after some preliminary tingling, a small papule forms, which soon shows a minute vesicle upon it. The vesicle enlarges, becomes flat, and is surrounded by a pink areola. After a time the fluid is absorbed from the centre, leaving a purplish depression, surrounded by the still vesicular periphery. Or the centre remains fluid, then comes a zone of purplish depression from absorption, then a peripheral zone still fluid, then the areola outside all. These zones of different colors suggest the name of iris. Sometimes complications arise from coalescence of extending patches. Recovery of any patch takes place in about a fortnight by fading of the areola, absorption of the fluid, and subsidence of the papule; but from repeated crops the whole disease may last from four to six weeks. The backs of the hands and fingers, especially on the radial half, and the insteps and knees, are the parts most affected; and the disease is generally symmetrical.

In the second variety there is a central bulla, and round this a ring of vesicles of smaller size. A second ring may form round the first, and a third round that. In some of these and allied cases of bullous erythema, the contents of the vesicles may be purulent, or sanguineous, and the process may extend deeply enough into the corium to produce ulcers which are followed by scars.

ERYTHEMA NODOSUM.

This consists of oval or circular solid flat elevations of the skin, from half an inch to one and a quarter inch in diameter, bright or dusky-red in color, gradually shading off into the surrounding skin, tender to the touch, and perhaps pitting slightly on pressure. They occur most often over the whole length of both tibiæ, and not infrequently over both ulna. Though rare in other parts, they have been seen on the calf, on the thighs, over the scapula, and over the condyles of the humerus. They come out more or less in crops, last seven to ten days, and gradually subside with bruise-like staining. They may become soft and fluctuate, but never suppurate. They are most common in children, and people under twenty years of age; and more frequent in girls than in boys. Their onset is preceded by some malaise, pains in the joints, and slight pyrexia.

Pathology of Erythema.-The essential change in erythema is an inflammation of the corium, with hyperemia and effusion of lymph and corpuscles. In different cases the process seems to be more intense at different levels in the skin structures: sometimes the skin alone is swollen, at others the epidermis is raised into blisters. Variations in intensity are shown by the contents of such vesicles as form, whether serum, pus, or blood; and by the amount of red corpuscles extravasated, whether a visible hemorrhage, or only enough to produce staining as recovery takes place.

Treatment. There is no specific treatment for the erythemata as such. Their cause, if it can be recognized, should be dealt with, and relief to discomfort about the lesions can be given by local means. In cases having a rheumatic origin, salicylate of soda should be given in doses of 15 or 20 grains three or more times in the day. If gastric troubles have caused the erythema, unsuitable articles of food should be withdrawn, such as shellfish, salt fish, pork, and sweets. Bicarbonate of sodium, bismuth, and gentian, should be given; or, in other cases, acids and nux vomica, according to the character of the gastric disorder. Locally, astringent and sedative lotions are of value, especially lead lotion (liq. plumbi subacet. dil.) combined with opium if there is much irritation, or calamine lotion or evaporating lotion of spirit and water, eau de Cologne, or liq. ammon. acetatis; in the drying or scabbing stages of the vesicular forms, zinc or zinc and lead ointment. In erythema nodosum, iron in combination with saline purgatives is generally the best remedy-e. g., the sulphates of iron and magnesia, with peppermint water.

ERYTHEMA PERNIO.

Pernio, or chilblain, is a superficial dermatitis, affecting the toes, sides of the feet, and the fingers, as a result of cold, in people of defective circulation, and especially in children. There are patches of dusky redness, with itching,