The book is divided into five parts. The first is devoted to a discussion of the action of roentgen rays and the gamma radiation of radium on the various tissues of the body. In many instances the dose of radiation that produces a reversible or an irreversible reaction in the tissues is given. In the second part are described the corpuscular rays and their effect on the body. In the third part ultraviolet light and its action, both direct and indirect, are discussed. Among the direct effects, to name but a few, sunburn and the bactericidal and antirachitic action of the rays are discussed, while among the indirect effects the action of the light on metabolism, respiration, circulation, the blood and the endocrine glands and its use in the treatment of tuberculosis are discussed. In the fourth part of the book attention is given to such subjects as the action