TEXT-BOOK OF PHYSIOLOGY 



CHAPTER I 

 INTRODUCTION 



An animal organism in the living condition exhibits a series of phe- 

 nomena which relate to growth, movement, mentality, and reproduction. 

 During the period preceding birth, as well as during the period included 

 between birth and adult life, the individual grows in size and complexity 

 from the introduction and assimilation of material from without. Through- 

 out its life the animal exhibits a series of movements, in virtue of which it 

 not only changes the relation of one part of its body to another, but also 

 changes its position relatively to its environment. If, in the execution of 

 these movements, the parts are directed to the overcoming of opposing 

 forces, such as gravity, friction, cohesion, elasticity, etc., the animal may 

 be said to be doing work. The result of normal growth is the attainment 

 of a physical development that will enable the animal, and, more especially, 

 man, to perform the work necessitated by the nature of its environment and 

 the character of its organization. In man, and probably in lower animals 

 as well, mentality manifests itself as intellect, feeling, and volition. At a 

 definite period in the life of the animal it reproduces itself, in consequence 

 of which the species to which it belongs is perpetuated. 



The study of the phenomena of growth, movement, mentality, and 

 reproduction constitutes the science of animal physiology. But as these 

 general activities are the resultant of and dependent on the special activities 

 of the individual structures of which an animal body is composed, physi- 

 ology in its more restricted and generally accepted sense is the science which 

 investigates the actions or functions of the individual organs and tissues of 

 the body and the physical and chemic conditions which underlie and 

 collectively determine all phenomena of life. 



Physiology may naturally be divided into: 



1. Individual physiology, the object of which is a study of the vital phenomena 

 'or functions exhibited by the organs of any individual animal. 



2. Comparative physiology, the object of which is a comparison of the 

 vital phenomena or functions exhibited by the organs of two or more 

 animals of different species, with a view to unfolding their points of 

 resemblance or dissimilarity. 



Human physiology is that department of physiologic science which 

 has for its object the study of the functions of the organs and tissues of 

 the human body in a state of health. 



Inasmuch as the study of function, or physiology, is associated with 

 and dependent on a knowledge of structure, or anatomy, it is essential that 



