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28 ance. As the eruption tends to disappear the scaling grows less, often disappearing from the centre of the patch and leaving a marginate ring. Finally the redness fades and the skin assumes a normal appearance, except in certain cases where pigmentation may occur.

In rare cases of psoriasis the eruption may tend to rapidly involve the whole skin. The cutaneous congestion is severe, and large flakes of partly detached epidermis may take the place of the silvery scales. In other words, an attack of acute



dermatitis exfoliativa has set in and complicated and obscured the psoriasis. When the dermatitis has subsided the psoriasis is very apt to reappear.

Psoriasis is not only a dry and scaly eruption, but it is invariably marginate. Whether occurring in small discs or in large, irregular patches, the border is always sharply defined and never shades off gradually into the surrounding healthy skin, as does the ordinary patch of eczema. This is a diagnostic point of great importance. In many cases of eczema the