[Illustration: _Muscular Coordination_ _Weissmuller’s horizontal plunge into a swimming pool._] POPULAR SCIENCE LIBRARY EDITOR-IN-CHIEF GARRETT P. SERVISS AUTHORS WILLIAM J. MILLER · HIPPOLYTE GRUENER · A. RUSSELL BOND D. W. HERING LOOMIS HAVEMEYER · ERNEST G. MARTIN ARTHUR SELWYN-BROWN · ROBERT CHENAULT GIVLER ERNEST INGERSOLL · WILFRED MASON BARTON WILLIAM B. SCOTT · ERNEST J. STREUBEL NORMAN TAYLOR · DAVID TODD CHARLES FITZHUGH TALMAN ROBIN BEACH ARRANGED IN SIXTEEN VOLUMES WITH A HISTORY OF SCIENCE, GLOSSARIES AND A GENERAL INDEX _ILLUSTRATED_ [Illustration] VOLUME NINE P. F. COLLIER & SON COMPANY NEW YORK Copyright 1922 BY P. F. COLLIER & SON COMPANY MANUFACTURED IN U. S. A. PHYSIOLOGY THE SCIENCE OF THE BODY BY ERNEST G. MARTIN PROFESSOR OF PHYSIOLOGY, STANFORD UNIVERSITY [Illustration] P. F. COLLIER & SON COMPANY NEW YORK PREFACE When Alexander Pope wrote “The proper study of mankind is man,” he was thinking rather of man as a social being than as the possessor of an amazingly complex and interesting body. It is nevertheless true that to one who finds enjoyment in the study of intricate mechanisms or to one for whom that amazing sequence of events which we call life has appeal there is no more fascinating study than the study of the living body. That part of the study of the body which concerns itself primarily with activity and only secondarily with form and structure, makes up the science of Physiology. The way the body works is the central theme.