By the term erythema multiforme I understand a disease characterized by certain tolerably well-defined erythematous lesions upon the skin, which undergo a variable evolution with a tendency to run an acute course and to recover spontaneously. The lesions are chiefly erythematous in type and are superficial, their seat being in the corium, especially in the papillary layer. They are not hyperemic but are distinctly exudative in character. They consist of macules, maculo-papules, papules, papulo-vesicles, vesicles and blebs. They manifest a disposition for one form to pass into another, thus frequently, but not always, constituting a multiform eruption, hence the name erythema multiforme, originally proposed for the disease by F. Hebra. While therefore a notable variety of lesions frequently, but not always, characterize the disease, it must not be supposed that every exudative erythema is necessarily an erythema multiforme. There are certain polymorphous erythemata which are to be classed as erythema