Notwithstanding the great war with its accompanying difficulties of publication, practically no delay has been occasioned in the appearance of the thirteenth volume of this encyclopedia. Physiologic optics is the outstanding topic of this volume, the article on which covers almost 500 pages: a large book in itself. Other important topics are the phorometer, the ocular relations of pituitary disease, ocular symptoms of poliomyelitis, ocular disturbances of pregnancy, and preparation for ophthalmic operations. Pliny the Elder, though not an ophthalmologist, was, like the editor of our present work, an encyclopedist, and his great and only surviving work, "Historia Naturalis," a compilation of contemporary Greco-Roman knowledge on a great variety of subjects, contains many references to the eye, its diseases and the remedies applied in their cure. From this material many pages of quotations appear in the present volume for the reason, as the editor says, that his observations on matters