VARIETIES.-- In the common form of psoriasis there are whitish minute spots, made up of dry, silvery-looking scales, heaped together on tawny-red patches of skin about the extensor aspects of the elbow and knee, and other places where the bones are near the surface ( P. Vulgaris); when the spots are larger, they resemble drops of mortar, and are found on the breast, back, and limbs (P. guttata); t