The disease begins as a superficial inflammation or hyperaemic spot, more or less circumscribed, slightly scaly, and which is soon followed by the formation of yellowish points about the hair follicles, surrounding the hair shaft. These yellowish points or crusts increase in size, become usually as large as small peas, are cup-shaped, with the convex side pressing down upon the papillary layer, and the concave side raised several lines above the level of the skin; they are umbilicated, friable, sulphur-colored, and usually each cup or disc is perforated by a hair. Upon removal or detachment, the underlying surface is found to be somewhat excavated, reddened, atrophied and sometimes suppurating. As the disease progresses the crusting becomes more or less confluent, forming irregular masses of thick, yellowish, mortar-like crusts or accumulations, having a peculiar, characteristic odor--that of mice, or stale, damp straw. The hairs are involved early in the disease, become brittle, lustreless, break off and fall out. In some instances, especially near the border of the crusts, are seen pustules or suppurating points. _Atrophy_ and more or less actual _scarring_ are sooner or later noted. Itching, variable as to degree, is usually present. #What is the course of favus of the scalp?# Persistent and slowly progressive. [Illustration: Fig. 66. Achorion Schoenleinii X 450. (_After Duhring._) Showing simple mycelium, in various stages of development, and free spores.] #What are the symptoms of favus when seated upon the general surface?# The symptoms are essentially similar to those upon the scalp, modified somewhat by the anatomical differences of the parts. The _nails_, when affected, become yellowish, more or less thickened, brittle and opaque (_tinea favosa unguium_, _onychomycosis favosa_). #To what is favus due?# Solely to the invasion of the cutaneous structures, especially the epidermal portion, by the vegetable parasite, the _achorion Schoenleinii_. It is contagious. It is a somewhat rare disease in the native-born, being chiefly observed among the foreign poor. The nails are rarely affected primarily. It is also met with in the lower animals, from which it is doubtless not infrequently communicated to man. #What are the diagnostic features of favus?# The yellow, and often cup-shaped, crusts, brittleness and loss of hair, atrophy, and the history. [Illustration: Fig. 67. Epilating Forceps.] #How would you distinguish favus from eczema and ringworm?# From eczema by the condition of the affected hair, the atrophic and scar-like areas, the odor, and the history. From ringworm by the crusting and the atrophy. In this latter disease there is usually but slight scaliness, and rarely any scarring. Finally, if necessary, a microscopic examination of the crusts may be made. #State the method of examination for fungus.#