WITHIN recent years many workers in the domain of physiology have made use of the more modern physical and chemical methods in their investigations, as is evident even from the most cursory study of present-day physiological and bio-chemical literature. Such a book, therefore, as that which Dr. Bayliss has just given us is of inestimable value to all who recognise that an approach to the study of physiology through the avenue of energetics is one that is bound to prove of great value. To deal satisfactorily with the principles of general physiology from this viewpoint requires, however, the expenditure of so much labour that at first sight it appears unlikely that one writer can take the whole burden upon his own shoulders. Dr. Bayliss has taken infinite pains in the preparation of a well-reasoned presentation of the physicochemical laws which govern vital processes. Every page shows evidence of a critical study of the literature, much of which, at least until recently, lay outside the region of the physiologist. One of the great advantages which will result from a careful study of this book will undoubtedly be the direction of the attention of the reader to the physicochemical literature of which the writer has made such good use.