This is a translation of Prof. Ziehen's “Leitfaden der Physiologischen Psychologie” (published in 1891), and we may say at once that to some extent it fills what is, or should have been, a long-felt want of the alienist. Unless we take into account Ladd's large and in many respects excellent work, there was no book in English which presented in a concise and handy form any statement of that general science of experimental psychology of which medical psychology is but a branch. Dr. Ziehen's book is well fitted to fill the void for two reasons—he is in sympathy with the English associational tendencies in psychology (in opposition to Wundt's doctrines), and he was moved to take up the general study of physiological psychology by the problems that came to him in the course of medico-psychological work. Although not appealing exclusively to the physician, this book is especially intended for (as the translators call him) the “psychiater.”