256 STUDIES IN ELECTRO-PHYSIOLOGY: 



be the same from the back and front when the " fault " is 

 equidistant, higher from the front when it is nearer to the 

 front, and higher at the back when it is nearer to the back, 

 but in practice the conditions of contact must be studied 

 and allowance made for them. As a rule, the skin of the 

 back is more oily or greasy than that of the chest. A little 

 experience, however, will enable the physician to make 

 correct diagnosis. 



In order to make clear much of that which in physiology 

 remains obscure it is only necessary to reason in terms of 

 highest potential of nerve-force in the brain and 

 differences of potential in the body, or, to put it another 

 way, in terms of hydrostatics ; the brain being the con- 

 stantly maintained head of water, the nerves the motor 

 and secretory paths the pipes through which it flows, and 

 differences of potential being differences of level. 



The sensory nerves may be compared with pipes filled 

 with water at an adjusted pressure, and the impulses 

 conveyed by them to the brain to the undulations or 

 vibrations transmitted through them by reason of any 

 disturbance of that adjustment. 



Thinking along those lines, we may more intelligently 

 conceive how and why it is that local pyrexia manifests 

 itself, electro-pathologically, as an expression of greater 

 quantity of nerve-current in the part affected. It is an 

 expression of lower level, because the resistance of the path 

 is lowered. Normally the resistance, if we consider it as 

 level, would be represented by the line ab in the following 

 diagram : 



..air 



Fig. 143A. 



The head of water the vertical line au remains unaltered 



