CHAPTEB V 

 APPLIED PHYSIOLOGY OF THE CIKCULATION 



IT might seem at first sight that our knowledge of the 

 circulation must be more precise and susceptible of more 

 direct clinical application than that of any other depart- 

 ment of physiology ; and to some extent, indeed, this is 

 true. It must be admitted, however, that when one 

 comes to apply this knowledge at the bedside, many gaps 

 are discoverable in it. This is due partly to our still 

 imperfect comprehension of the physical laws which 

 govern the circulation of fluids in a closed system of 

 tubes, and partly to our ignorance of the extent to which 

 such laws are applicable to the conditions which obtain 

 in the living body. The problems presented by dis- 

 orders of the circulation, moreover, are rendered still 

 more difficult by the complicated nature of the checks, 

 adjustments, and compensations which are exhibited in it 

 under the sway of nervous influences, the precise nature 

 and mode of action of which we are still far from fully 

 comprehending even in health, to say nothing of disease. 

 Much attention, however, is now being devoted to the 

 exact study of disorders of the circulation by physical 

 methods, which the invention of instruments of pre- 

 cision has rendered possible, and there can be no doubt 



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