CHAPTER I 

 INTRODUCTION 



PHYSIOLOGY in its widest sense signifies the study of the phenomena pre- 

 sented by living organisms, the classification of these phenomena, and the 

 recognition of their sequence arid relative significance. Such a range would 

 include many studies which are not generally grouped under the term 

 physiology, and would in fact correspond to the comprehensive science of 

 biology. Thus the study of the relations of living beings to one another and 

 to their surroundings is the special object of the science of cecology. The 

 aims of physiology in its restricted sense are the description, analysis, and 

 classification of the phenomena presented by the isolated organism, the 

 allocation of every function to its appropriate organ, and the study of the 

 conditions and mechanisms which determine each function. 



The fundamental phenomena of life are essentially identical throughout 

 the whole series of living organisms. This continuity of function is the 

 necessary correlation of the continuity of descent, which brings into relation 

 all members of the animal and vegetable kingdoms. No living organism 

 can therefore be regarded as outside the sphere of our investigations. The 

 interest of mankind in this subject was, however, naturally awakened iri 

 connection with his own body, and the science, growing up as ancillary and 

 preliminary to medical studies, has always taken man as its chief type of 

 study. In the present work the elucidation of the functions of man will 

 also be our first concern, and this for two reasons. In the first place, 

 in physiology, as in all other sciences, the motive of man's activity is his 

 social instinct to increase the power of his race in the struggle for existence, 

 by the acquisition of control, either over the external forces of nature, 

 which may be turned to his own benefit, or over the factors, intrinsic and 

 extrinsic, which tend to his enfeeblement or extirpation by disease and death. 

 Consciously or unconsciously, all our researches on physiology, whether on 

 the higher animals or on the lowest protozoa, have the welfare of man as 

 their ultimate object. In the second place, the choice of the higher animals 

 as our chief objects of study receives justification from the fact that whereas 

 morphology, or the science of structure, must proceed from the lowest to 

 the highest organisation, the science of function presents its problems in 

 their simplest form in the most highly differentiated organisms. In the 

 unicellular animal all the essential functions which we associate with Jiving 

 beings are carried out, often simultaneously, in one little speck of proto- 

 plasm. An analysis of these functions, the determination of their conditions 



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