6 RESPONSE IN TJIE LIVING AND NON-LIVING 



similar changes taking place at both points, and there 

 being thus no relative difference between the two, the 

 galvanometer will still indicate no current. This null- 

 effect is due to the balancing action of B as against A. 

 (See fig. 2, a.} 



Conditions for obtaining electric response If then 

 we wish to detect the response by means of the galvano- 

 meter, one means of doing so will lie in the abolition of 

 this balance, which may be accomplished by making 

 one of the two points, say B, more or less permanently 



A B A B 



< Current of Injury 



> Current of Action, 



FIG. 2. ELECTRIC METHOD OF DETECTING NERVE KESPONSE 



(a) Iso-electric contacts ; no current in the galvanometer. 



(b) The end B injured ; current of injury from B to A : stimulation gives rise to 



an action current from A to B. 



(c) Non-polarisable electrode. 



irresponsive. In that case, stimulus will cause greater 

 electrical disturbance at the more responsive point, 

 say A, and this will be shown by the galvanometer as a 

 current of response. To make B less responsive we 

 may injure it by means of a cross-sectional cut, a burn, 

 or the action of strong chemical reagents. 



Current of injury. We shall revert to the subject of 

 electric response; meanwhile it is necessary to say a few 

 words regarding the electric disturbance caused by the injury 

 itself. Since the physico-chemical conditions of the uninjured 

 A and the injured B are now no longer the same, it follows 





