RINGWORM (or TINEA TONSURANS)  , a disease of the scalp (especially common within the tropics); it consists of bald patches, usually round, and varying in diameter from half an inch up to several inches, the surface showing the broken stumps of hairs and a fine whitish powdering of desquamated epidermic scales . In scrofulous subjects matter is sometimes produced, which forms crusts, or glues the hair together, or otherwise obscures the characteristic appearance . The disease is due to a parasite, Trichophyton tonsurans, which exists mostly in the form of innumerable spores (with hardly any mycelium), and is most abundant within the substance of the hairs, especially at their roots . If a piece of the hair near the root be soaked for a time in dilute liquor potassae and Dressed flat under a cover-glass, the microscope will show it to be occupied by long rows of minute oval spores, very uniform in size, and each bearing a nucleus . The same fungus sometimes attacks the hairs of the beard, producing a 'disease called " sycosis." Sometimes it invades the hairless regions of skin, forming " tinea circinata "; circular patches of skin disease, if they be sharply defined by a margin of papules or vesicles, may be suspected of depending on the tinea-fungus . Interesting varieties of tinea are found in some of the Pacific and East Indian islands . Among the best remedial agents are various mercurial preparations . But in modern practice much success has been found in X-raying the patch in order to remove the dead and diseased hairs, thus leaving a free channel for the passage of antiseptic applications to the follicles . The exposures are followed by inunction of a mercurial preparation or of a lotion of tincture of iodine with methylated spirit . See also FAVUS .