A portion of the crust is moistened with liquor potassae and examined with a power of three to five hundred diameters. The fungus, (achorion Schoenleinii), consisting of mycelium and spores, is luxuriant and is readily detected. #State the prognosis of favus.# Upon the scalp, favus is extremely chronic and rebellious to treatment, and a cure in six to twelve months may be considered satisfactory; in neglected cases permanent baldness, atrophy, and scarring sooner or later result. Although favus of the scalp persists into adult life, it becomes less active and, finally, as a rule, gradually disappears, leaving behind scarred or atrophic bald areas. Upon the general surface it usually responds readily to treatment, excepting favus of the nails, which is always obstinate. #How is favus of the scalp treated?# Treatment is entirely local and consists in keeping the parts free from crusts, in epilation and applications of a parasiticide. The crusts are removed by oily applications and soap-and-water washings. The hair on and around the diseased parts is to be kept closely cut, and, when practicable, depilation, or extraction of the affected hairs, is advised; this latter is, in most cases, essential to a cure. Remedial applications--the so-called parasiticides--are, as a rule, to be made twice daily. If an ointment is used, it is to be thoroughly rubbed in; if a lotion, it is to be dabbed on for several minutes and allowed to soak in. #Name the most important parasiticides.# Corrosive sublimate, one to four grains to an ounce of alcohol and water; carbolic acid, one part to three or more parts of glycerine; a ten per cent. oleate of mercury; ointments of ammoniated mercury, sulphur and tar; and sulphurous acid, pure or diluted. The following is valuable:-- [Rx] Sulphur, praecip., .................... [dram]ij Saponis viridis, Ol. cadini, ....... [=a][=a] ......... [dram]j Adipis, .............................. [Oz]ss. M. Chrysarobin is a valuable remedy, but must be used with caution; it may be employed as an ointment, five to ten per cent. strength, as a rubber plaster, or as a paint, a drachm to an ounce of gutta-percha solution. Formalin, weakened or full strength, has been extolled. Some observers have experimentally tried the effect of _x_-ray exposure with alleged good results, pushing the treatment to the point of producing depilation; if used great caution should be exercised. #How is favus upon the general surface to be treated?# In the same general manner as favus of the scalp, but the remedies employed should be somewhat weaker. In favus of the nail frequent and close paring of the affected part and the application, twice daily, of one of the milder parasiticides, will eventually lead to a good result. #Is constitutional treatment of any value in favus?#