CHAPTER I 

 INTRODUCTION 



PHYSIOLOGY in its widest sense signifies the study of the phenomena 

 presented by living organisms, the classification of these phenomena, 

 and the recognition of their sequence and 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 com- 

 prehensive 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 in 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 extir- 

 pation 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 



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