raised and to have a brownish tinge. Presently the centre of this brownish patch— perhaps a quarter of an inch in diameter— gives way and a ring of scaling epidermis, attached at the periphery, but free, ragged, and slightly elevated towards the centre of the spot, is formed. In a few days this ring of epidermis has extended so as to include a larger area. A second brown spot then appears at the site of the first brown spot and in the centre of the primary scaling, expanding ring. This second spot, in its turn, gives way, producing a second and similar scaling ring, which also expands, following the first ring in its extension. Later a third and fourth ring form in the same way; and so on, until a large area of skin is covered with one or more systems of concentric parallel scaling rings, which follow each other over the surface of the body like the concentric ripples produced by a stone falling into a pool of water.
The scales, if not broken by rubbing, may attain considerable length and breadth; but, of course, their dimensions are in a measure determined by the amount of friction they are subjected to. Usually they are largest between the shoulders— that is, where the patient has a difficulty in scratching himself. The lines of scales are from ⅛–½ in. apart. The hair of the scalp is not injured.
The fundus.— On detaching a scale and placing it under the microscope, after moistening with liquor potassæ, a trichophy ton-like fungus can be seen in enormous profusion. The parasite evidently lies between epidermis and rete, and by its abundance causes the. former to peel up. As the fungus does not die out in the skin travelled over, it burrows under the young epithelium almost as soon as the latter is reproduced. Hence the peculiar concentric scaling and the persistency of the disease throughout the area involved. When the scales are washed off by the vigorous use of soft soap and hot water, the surface of the skin is seen to be covered with parallel lines of a brownish colour— evidently the slightly pigmented fungus proliferating and advancing under the young epidermis. Tribondeau, on the evidence
