The skin from its position is much exposed to tubercular infection. The cutaneous surface, however, cannot be regarded as very susceptible to this infection. Tuberculosis varies somewhat according to the region of the skin which is affected. The most frequent and characteristic form is Lupus.

Lupus occurs mostly in children, and attacks chiefly the face. The tubercle bacillus having obtained a tooting produces an advancing infiltration of the cutis with granulation tissue, in the midst of which giant-cells are frequently visible and sometimes defined tubercles. These, however, are apt to be overwhelmed by the cellular infiltration. There is commonly an exaggeration of the epidermis, so that epidemic processes may penetrate somewhat among the granulation tissue. With all this there is a destruction of the specific structures of tla-skin. The sebaceous glands and hair follicles are destroyed, bat it is said that the sweat glands, being situated beneath the cutis, are spared.

The tubercular new-formation undergoes degenerative changes, which lead frequently to ulceration, but sometimes cause cicatrization without ulceration.

The appearances presented to the naked eye vary considerably. There is a local infiltration of the skin, giving an irregular raised surface. The thickening may be very great (L. hypertrophicus); or there may be considerable thickening and desquamation of the epidermis (L. exfoliativa). Ulceration is frequently manifest (L. exedens or ulcerans), and the ulcers are often very varied in shape; or ulceration may be absent (L. non-exedens).

Lupus is not usually accompanied by tubercular manifestations in other parts, except that the associated lymphatic glands are not infrequently affected.

Scrofuloderma is a term whose definition from lupus is not easily made. It is mostly secondary to tuberculosis in the glands or subcutaneous tissue. The primary seat being usually beneath the cutis the latter is attacked irregularly, and there may be, over an extended surface, many irregular swellings with ulcerations. There may be great thickening of the skin, such as to cause some resemblance to elephantiasis in cases where the leg is affected.

The Pathological wart has all the characters of lupus, consisting in a tuberculosis of the skin. It arises by inoculation of the tubercle bacillus in the course of post-mortem work. There is at first a more or less acute localized inflammation, which gradually subsides into a chronic thickening, the surface of which often shows exaggerated papillae like those of a wart. There is not much tendency to extension, and not much inclination to healing.