F PHYSIOLOG 



TEXT- 



CHAPTER i. 

 INTRODUCTION. 



An animal organism in the living condition exhibits a series of 

 phenomena which relate to growth, movement, mentality, and re- 

 production. 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. Throughout 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 posi- 

 tion 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, physiology 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 determine 

 them.^ 



This may naturally be divided into: 



i. Special physiology, the object of which is a study of the vital 

 phenomena or functions exhibited by the organs of any individual 

 animal. 



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