The practical value of Physiology to the general reader lies in the fact that it forms the basis of all sound rules of hygiene. Life is made up of bodily activities which may be carried on correctly or incorrectly. Carried on correctly they mean health, carried on incorrectly, unhealth. The world is flooded with health-preserving or health-restoring systems, urged upon the public, for the most part, by promoters in search of gain. Such of these as have merit are based on definite physiological principles, and anyone who has a common-sense working knowledge of his own body can order his life in accordance with them, at little or no expense. Moreover, a sound appreciation of Physiology drives home the truth that when the body is really out of order its restoration can be safely intrusted only to the properly trained physician: the man or woman who through years of painstaking study has won insight into the intricacies of the human mechanism and whose honest appreciation of the difficulties of his profession, and courageous sincerity in grappling with them, justify to the full the confidence in which he is held by his community. ERNEST G. MARTIN. CONTENTS CHAPTER PAGE I. THE SIGNS OF LIFE 9 II. THE MAINTAINING OF LIFE 18 III. THE SOURCES OF FOOD 24 IV. THE USES OF FOOD 31 V. BODY CELLS 41 VI. THE SUPPORTING FRAMEWORK 53 VII. MOTION 73 VIII. SENSATION--INTERNAL AND CONTACT SENSES 86 IX. SENSATION--DISTANCE SENSES 96 X. THE NERVOUS SYSTEM AND SIMPLE NERVOUS ACTIONS 122 XI. THE BRAIN AND COMPLEX NERVOUS ACTIONS 139 XII. SOME SPECIAL NERVOUS ACTIONS; SMOOTH MUSCLE AND GLAND CONTROL 155 XIII. THE BODY FLUIDS 173 XIV. THE CONVEYER SYSTEM OF THE BODY 191 XV. THE SERVICE OF SUPPLY OF FOOD 226 XVI. THE SERVICE OF SUPPLY OF OXYGEN 253 XVII. THE SERVICE OF REMOVAL OF WASTE 271 XVIII. MORE ABOUT THE USE OF FOOD BY THE BODY 277 XIX. KEEPING WARM IN WINTER AND COOL IN SUMMER 305 XX. THE PERPETUATION OF THE RACE 324 XXI. CHILD AND MAN 345 LIST OF ILLUSTRATIONS