That certain micro-organisms can, by direct implantation, give rise to disorders of keratinization, notably localized hyperkeratosis, is an accepted fact clinically and bacteriologically. Thus, the etiologic rôle of the gonococcus in the production of blenorrhagic keratoses, the tubercle bacillus in its relation to verruca necrogenica, and the gonococcus and pus organisms as causative agents in the production of acuminate condylomas stand out as striking examples of the aforementioned fact.
In explanation of. the etiologic factor in the production of common warts there have been advanced at various times the opinions that they are caused by an infecting organism, trauma or a foreign body. There are many clinical examples which stand out in favor of each of these hypotheses. The frequency with which verrucae occur at points of trauma, notably on the hands and feet, would at first glance speak strongly for trauma as