INTRODUCTION. 



Physiology treats of the functions or actions of living beings. 



When these actions or functions occur in a disturbed or irregular 

 manner, they constitute disease, or abnormal life, and become the subject 

 of abnormal physiology or pathology. Normal physiology is the basis of 

 pathology, and a knowledge of the one must precede the intelligent study 

 of the other: just as an acquaintance with the functions of the com- 

 ponent parts of a machine must precede the recognition of disordered 

 movement and the provision of means of repair. 



Since the functions of the animal body are resident in the various 

 tissues and organs of the body, an acquaintance with the forms and 

 structure of those organs and tissues must precede the study of their 

 functions. The study of anatomy and histology, or microscopic anat- 

 omy, must therefore precede the study of physiology. 



General Physiology treats of the functions of organized beings in 

 an abstract manner, — that which regards the general laws of life, whether 

 seen in the animal or vegetable world. Although for the purposes of 

 practical life physiology is divided into several provinces, yet the knowl- 

 edge of general physiology is essential even to special students, since 

 the relation between the different forms of life is very close. 



Vegetable Physiology is concerned solely with the consideration 

 of the vital actions or functions of plants. 



Comparative Physiology treats of the functions of animals below 

 man, with a consideration of the means by which different functions are 

 accomplished by different animal forms. 



Special Physiology is confined to the consideration of the vital 

 phenomena of a single species, single genus, or it may deal with the 

 consideration of a special function. In this book special physiology 

 will refer mainly to the study of the vital phenomena of the domestic 

 animals. 



Human Physiology treats exclusively of the vital phenomena of 

 man. But, while this branch of physiology is of greater importance to 

 the physician than the other divisions, in consequence of its relations 

 to human pathology and therapeutics, it should not be made the exclu- 

 sive subject of study; for the physiology of man cannot be properly 

 understood without a previous acquaintance with the vital phenomena of 



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