The patches spread by the appearance of new tubercles, or infiltrations at the peripheral portion. New islets and areas of disease may continue to make their appearance from time to time, usually upon contiguous parts. #Are the mucous membranes of the mouth, throat and larynx ever involved?# In some instances, and either primarily or secondarily. [Illustration: Lupus Vulgaris.] [Illustration: Lupus Vulgaris.] #Is the bone tissue ever involved in lupus vulgaris?# No. #What course does lupus vulgaris pursue?# It is slowly but, as a rule, steadily progressive. Several years or more may elapse before the area of disease is conspicuous. #What is the cause of lupus vulgaris?# It is now known to be due to the invasion of the cutaneous structures by the tubercle bacillus; in short, a tuberculosis of the skin. It is not infrequently observed in the strumous and debilitated. It is entirely independent of syphilis. #What is the pathology of lupus vulgaris?# According to recent investigations, the infiltrations of lupus are due chiefly to cell-proliferation and outgrowth from the protoplasmic walls and adventitia of the bloodvessels and lymphatics. The fibrous-tissue network, vessels and a portion of the cell infiltration are thus produced, the fixed and wandering connective-tissue cells of the inflamed stroma of the cutis being responsible for the other portion of the new growth (Robinson). #State the diagnostic features of lupus vulgaris.# In a typical, developed patch of lupus are to be seen:--cicatricial formation, usually of a fibrous and tough character; ulcerations; the yellowish-brown tubercles and infiltration; and the characteristic soft, small, yellowish or reddish-brown, cutaneous and subcutaneous points and tubercles. #How does the tubercular syphiloderm differ from lupus vulgaris?# The tubercular syphiloderm is much more rapid in its course, the ulceration is deeper and the discharge copious and often offensive; the scarring is soft, and, compared to the amount of ulceration, but slightly disfiguring; and it is, for obvious reasons, a disease of adult or late life. The history, together with other evidences of previous or concomitant symptoms of syphilis, will often aid in the differentiation. #How does epithelioma differ from lupus vulgaris?# The edges of the epitheliomatous ulcer are hard, elevated and waxy; the base is uneven, the secretion thin, scanty and apt to be streaked with blood; the ulceration usually starts from one point, and is often painful; the tissue destruction may be considerable; there is little, if any, tendency to the formation of cicatricial tissue; and, finally, it is usually a disease of advanced age. #In what respects does lupus erythematosus differ from lupus vulgaris?# Lupus erythematosus has no papules, tubercles or ulceration. #How does acne rosacea differ from lupus vulgaris?#