Abstract
Morphology must always be the basis of clinical medicine, but it does not satisfy the desire for causality. In addition to many other advances in the study of endocrine organs, in the sympathetic and parasympathetic nervous systems, in heredity and in medical chemistry, it is immune biologic knowledge in a general sense of the word which has been the principal aid in the understanding of the pathogenesis of skin lesions. The application of this knowledge to morphology not only increases the interest of the clinic in dermatoses, but is also of use in diagnosis and of great heuristic value, especially in those diseases the etiology of which is as yet unknown. A systematic review of this subject seems to be lacking in the literature. I cannot give such a review here but should like to show roughly that the study of the form of skin lesions has been advanced through