In offering this book to you, reader, I feel that I must justify its publication. I admit freely that more could be said for a finished study in which hypotheses were replaced by exact fact. But to get together assured results in a field so little explored is a great task, calling for time and much labour. I remembered the adage, “_Ars longa, vita brevis_,” and I decided to publish what is really a programme of work to be carried out as fully as circumstances may permit. At all events, I hope that such a programme may have its value for younger investigators, who wish a point of orientation for their labours. My book is addressed to disciplined minds, and in especial to biologists. As I wrote it, I had not the general public in my mind, and so I did not hesitate to devote nearly the whole of a chapter to “disharmonies in the apparatus of reproduction.” I see in that apparatus the clearest proof of the essential disharmony in the organisation of man. I have to thank those friends who were familiar with my views and whose advice and assistance have helped me to develop them. In particular, I desire to thank my friends Dr. E. Roux, who was at the pains to make my French more French; and Dr. J. Goldschmidt and Dr. Mesnil, who have read and revised the proof-sheets. ÉLIE METCHNIKOFF. PARIS, _February 8, 1903_. CONTENTS _Page_ EDITOR’S INTRODUCTION iii AUTHOR’S PREFACE ix PART I DISHARMONIES IN THE NATURE OF MAN CHAPTER I INTRODUCTION—SUMMARY OF OPINIONS ON THE NATURE OF MAN 3 Importance of the study of the nature of man—The nature of man as the foundation of morality—Greek worship of human nature—Matriopathy of ancient philosophers—Rationalism of the eighteenth and nineteenth centuries—Degradation of human nature by religious doctrines—Influence of these conceptions on actual life and on art—Reaction of the Reformation against the degradation of human nature—Mutilation of the human body by primitive races CHAPTER II HARMONIES AND DISHARMONIES AMONGST BEINGS INFERIOR TO MAN 17