_Antivenomous serum-therapy_, which my studies, supplemented by those of Phisalix and Bertrand, Fraser, George Lamb, F. Tidswell, McFarland, and Vital Brazil, have enabled me to establish upon scientific bases, has now entered into current medical practice. In each of the countries in which venomous bites represent an important cause of mortality in the case of human beings and domestic animals, special laboratories have been officially organised for the preparation of antivenomous serum. All that remains to be done is to teach its use to those who are ignorant of it, especially to the indigenous inhabitants of tropical countries, where snakes are more especially formidable and deadly. This book will not reach such people as these, but the medical men, naturalists, travellers, and explorers to whom it is addressed will know how to popularise and apply the information that it will give them. I firmly believe also that physiologists will read the book with profit. Its perusal will perhaps suggest to them the task of investigating a host of questions, which are still obscure, relating to toxins, their mode of action upon the different organisms, and their relations to the antitoxins. There is no doubt that in the study of venoms a multitude of workers will, for a long time to come, find material for the exercise of their powers of research. * * * * * At the moment of completing this work I would like to be allowed to cast a backward glance upon the stage that it marks in my scientific career, and to express my heartfelt gratitude to my very dear master and friend, Dr. Émile Roux, to whom I owe the extreme gratification of having been able to dedicate my life to the study of experimental science, and of having caused to germinate, grow, and ripen a few of the ever fertile seeds that he sows broadcast around him. * * * * * I am especially grateful to those of my pupils, C. Guérin, A. Deléarde, F. Noc, L. Massol, Bernard, and A. Briot, who have helped me in my work, while showering upon me the marks of their confidence, esteem, and attachment; to my former chiefs, colleagues, and friends of the Colonial Medical Staff, Drs. G. Treille, Kermorgant, Paul Gouzien, Pineau, Camail, Angier, Lépinay, Lecorre, Gries, Lhomme, and Mirville; and to my numerous foreign or French correspondents, George Lamb, Semple, C. J. Martin, Vital Brazil, Arnold, de Castro, Simon Flexner, Noguchi, P. Kyes, Morgenroth, J. Claine, Piotbey, and R. P. Travers, several of whom have come to work in my laboratory, or have obligingly procured for me venoms and venomous animals.