PHYSIOLOGY 



CHAPTER I 

 GENERAL INTRODUCTION 



Physiology is the science that treats of the functions of normal 

 living matter. As living matter may be either of animals 

 or of plants, so there is a separation of physiology into corre- 

 sponding divisions animal and vegetable. 



Human physiology consists of those facts of animal physiology 

 which have been derived from experiments upon human beings, 

 together with much that has been ascertained for closely 

 allied animals and can be inferred to hold true for man. The 

 chemistry of living things is now a distinct science physio- 

 logical chemistry although it was not so formerly. The term 

 physiology, derived from the Greek words ^v6iq and Adyof, 

 is synonymous etymologically in its broadest application and 

 acceptation with natural philosophy, and the earliest physio- 

 logical conceptions were formed in prehistoric times, inseparable 

 as such from the general mass of knowledge which during the 

 course of later centuries grew into theological, scientific, philo- 

 sophical, and other aggregations of ideas. 



The science of physiology as it exists today has been gradually 

 evolved out of the joint labors of thousands and thousands 

 of workers. Of these, there are some that stand preeminent 

 and mark in a way the principal epochs in the history of the 

 subject. In the earliest times among the philosophers who 

 dealt with problems that are now physiological may be men- 

 tioned Empedocles, Hippocrates, Heracleitus, and particularly 

 Aristotle (384-322 B.C.). Galen (131 to about 200 A.D.) dis- 

 tinctly recognized the nature and importance of physiology, 

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