These scholars and inquirers, with Bacon, believe that the only science is general science. What they want to know is not what instruments we use, our processes, our technique, and the thousand and one details of the experiments on which we spend our lives in the laboratory. What they are interested in are the general truths we have acquired, the problems we are trying to solve, the principles of our methods, the progress of our science in the past, its state in the present, its probable course in the future. But I venture to think that this book is also addressed to another class of readers, to those whose professional study is physiology. To them it is dedicated. They have been initiated into the mysteries of the science. They are learning it by practice. That is the right method. Practice makes perfect. Claude Bernard used to say that in order to be an expert in experimental science you must first be “a laboratory rat.” And among us there are many such “laboratory rats.” They are guided in the daily task of investigation by a dim instinct of the path and of the direction of contemporary physiology. Perhaps it may be of assistance to them to find their more or less unconscious ideas here expressed in an explicit form. A. DASTRE. CONTENTS. BOOK I. THE FRONTIERS OF SCIENCE. GENERAL THEORIES OF LIFE AND DEATH. THEIR SUCCESSIVE TRANSFORMATIONS. CHAP. PAGE I. EARLY THEORIES 1 II. ANIMISM 5 III. VITALISM 15 IV. THE MONISTIC THEORY 34 V. THE EMANCIPATION OF SCIENTIFIC RESEARCH FROM THE YOKE OF PHILOSOPHICAL DOCTRINE 42 BOOK II. THE DOCTRINE OF ENERGY AND THE LIVING WORLD. GENERAL IDEAS OF LIFE. ALIMENTARY LIFE. I. ENERGY IN GENERAL 57 II. ENERGY IN BIOLOGY 97 III. ALIMENTARY ENERGETICS 116 BOOK III. THE CHARACTERS COMMON TO LIVING BEINGS. I. DOCTRINE OF VITAL UNITY 146 II. MORPHOLOGICAL UNITY OF LIVING BEINGS 157 III. CHEMICAL UNITY OF LIVING BEINGS 173 IV. TWOFOLD CONDITIONS OF VITAL PHENOMENA. IRRITABILITY 188 V. THE SPECIFIC FORM: ITS ACQUISITION, ITS REPARATION 199 VI. NUTRITION. FUNCTIONAL ASSIMILATION. FUNCTIONAL DISTRIBUTION. ASSIMILATING SYNTHESIS 209 BOOK IV. THE LIFE OF MATTER.