The thought would naturally occur to one familiar with the many etiologic factors which have been suggested as causative of psoriasis, why write on such a hackneyed subject unless something definite can be stated? I have written this short article with the sole purpose of eliminating one of the most frequently mentioned causative factors—heredity. So much has been mentioned in regard to the diseases of the forebears descending to the offspring, either of the next younger generation or, skipping these descendants, those of the second period, that a careful study has been made of the cases of psoriasis to eliminate this causative factor.
Various writers have attributed a large number of their cases of psoriasis to a hereditary cause. Wilson, according to his studies, found evidence of hereditary causation in 30 per cent. of his cases, Payne in 22 per cent., Abraham in 16 per cent., Rosenthal in