A TEXT-BOOK OF PHYSIOLOGY 



INTRODUCTION 



The aim of scientific physiology is, to determine the functions of the animal body and to 

 derive them strictly from the elementary conditions of animal life (LUDWIG). 



THE animal body is composed of a large number of different organs. The 

 first task therefore is to find out what functions are performed by each indi- 

 vidual organ, to learn how these functions may be influenced by different 

 conditions, and to determine as exactly as possible the intensity with which 

 each function may be performed under different circumstances. 



Of all the varying conditions, whose influence on the functions of the 

 organs we shall have to investigate, there is none so important as the action 

 of the organs themselves upon one another, and the consequent manifold 

 interdependence among them. It is only by giving attention to this inter- 

 action of the organs that we can arrive at any real determination of their 

 functions, or make any satisfactory progress toward understanding how the 

 existence and capabilities of the body as a whole result from the collective 

 activity of the individual organs. 



In most of the functions the activity of the elementary constituents of the 

 body, the cells and tissues, is to be reckoned as a fundamental condition. And 

 the farther modern physiology progresses, the more clearly does it appear 

 that the cell, or as Briicke appropriately calls it, the elementary organism, 

 represents the real unit of the body, not only in the morphological sense, but 

 in the physiological sense as well. The remarkable properties of the living 

 substance, as exhibited in most of the fundamental processes going on in the 

 living body, are dependent upon much more complicated conditions than the 

 exact scientific investigations of our time have been able to explain; but in 

 most physiological problems where research has progressed far enough to 

 warrant theoretical conclusions to any degree well founded, it has been shown 

 that the fundamental conditions for the functions of the organs and tissues 

 are precisely those conditions which determine the vital activity of the cells. 

 It need scarcely be emphasized here that in so saying I have meant to give 

 no actual theory, that is to say, no mechanical explanation, of the phenomena 

 in question. If we trace the functions of the organs back to the vital activity 

 of the cell, we have done nothing more than point out where the solution of 

 the problem is ultimately to be sought, without having thereby entered more 

 deeply into the problem. 



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