_Tar_ is, all things considered, the most important external remedy. It is comparatively slow in its action, but is useful in almost all cases. As employed usually it is prescribed in ointment form, either as the official tar ointment, full strength or weakened with lard or petrolatum. It may also be used as pix liquida, with equal part of alcohol. Or the tar oils, oil of cade (ol. cadini), and oil of birch (ol. rusci) may be employed, either as oily applications or incorporated with ointment or with alcohol. Liquor carbonis detergens, in ointment, one to three drachms to the ounce of simple cerate and lanolin is a mild tarry application which is often useful. In stubborn patches an occasional thorough rubbing with a mixture of equal parts of liquor carbonis detergens and Vleminckx's solution, followed by a mild ointment, sometimes proves of value. In whatsoever form tar is employed it should be thoroughly rubbed in, once or twice daily, the excess wiped off, and the parts then dusted with starch or similar powder. _Ammoniated mercury_ is applied in ointment form, twenty to sixty grains to the ounce. Compared to other remedies it is clean and free from staining, although, as a rule, not so uniformly efficacious. It is especially useful for application to the scalp and exposed parts. It should not be used over extensive surface for fear of absorption. _[beta]-Naphthol_ and _resorcin_ are applied as ointments, thirty to sixty grains to the ounce, and as they are (especially the former) practically free from staining, may be used for exposed surfaces. Gallacetophenone and aristol also act well in some cases, applied in five- to ten-per-cent. strength, as ointments. In obstinate patches the _x_-ray may be resorted to, employing it with caution and in the same manner as in other diseases. #Pityriasis Rosea.# (_Synonym:_ Pityriasis Maculata et Circinata.) #What do you understand by pityriasis rosea?# Pityriasis rosea is a disease of a mildly inflammatory nature, characterized by discrete, and later frequently confluent, variously sized, slightly raised scaly macules of a pinkish to rosy-red, often salmon-tinged, color. #Upon what part of the body is the eruption usually found?# The trunk is the chief seat of the eruption, although not infrequently it is more or less general. #Describe the symptoms of pityriasis rosea.# The lesions, which appear rapidly or slowly, are but slightly elevated, somewhat scaly, usually rounded, except when several coalesce, when an irregularly outlined patch results. At first they are pale or bright pink or reddish, later a salmon tint (which is often characteristic) is noticed. The scaliness is bran-like or flaky, of a dirty gray color, and, as a rule, less marked in the central portion; it is never abundant. The skin is rarely thickened, the process being usually exceedingly superficial. #What course does pityriasis rosea pursue?#