Erythematous Diseases

The diseases which rank under this head as having simply erythema as their primary and only feature are exceedingly simple and well denned. They are three: erythema, roseola, and urticaria. These erythemata are characterized mainly by the occurrence of active hyperaemia of the longitudinal plexus of the skin (erythema), and 'its immediate consequences - for example, serous effusion - nothing more. In erythematous diseases the redness may be rosy (roseola), or bright red (erythema urticaria); in urticaria "wheals" are present. The erythema in these diseases is removable by pressure. Unlike the more common eruptive diseases of the skin, the erythemata exhibit the closest connection between local and constitutional phenomena. Febrile symptoms antecede and are relieved by the development of the erythema in the exanthemata, showing that the local skin changes are secondary, and only parts of a general disturbance which is primary. I shall include under this head sections on follicular hyperaemia, pellagra, and certain medicinal rashes.