Photodynamic Action and Diseases Caused by Light.

This book should prove of interest, although perhaps not of great practical value, to any member of the medical profession. The first chapters discuss the quantum theory of light and its application to biologic phenomena which occur under the influence of light rays, including those beyond the visible range. The distinction between the mode of action of ultraviolet light and that of light of the longer wavelengths is of interest, since the former acts directly on living tissue and the latter requires the mediation of some such substance as a photosensitive dye and oxygen. Examples of the latter mode of action are found in diseases of sheep, hypericum (St.-John's-wort) poisoning andGeldekopf. The situation with regard to human diseases is not so clear. On the basis of the evidence presented, the author questions that hematoporphyrin plays a role as a sensitizing factor, such as has been postulated in hydroa aestivale