214 PHYSIOLOGY CHAP. 



These conclusions (as Boruttau pointed out) are partially 

 based upon the theoretical fallacy that the magnitude of the 

 galvanometer swing is an exact measure of the strength of the 

 current of action. This is not correct. The magnitude of the 

 galvanometer deflection is a result not merely of the strength of 

 the current but also of its duration. Admitting that the cessation 

 of deflections on the galvanometer indicates the disappearance of 

 the action current, it is not, on the other hand, legitimate to 

 assume that an increase in these deflections must represent an 

 increase of the action current and a rise of excitability. To study 

 the period of the current of action it is necessary to employ the 

 capillary electrometer, the oscillations of which can be photographed. 



fmm 



FIG. 140. Photograph. (Waller.) Shows that prolonged tetanisation of the nerve 

 (at T from a to w) has the same exciting action on the electrical vaiiations of 

 the nerve as a small amount of CO 2 . 



Boruttau and Frb'hlich (1904) were able, by this method, to show 

 that the action current in the nerve treated with alcohol, ether, 

 chloroform, and carbonic acid really suffers a decrement the 

 amount of which is in ratio with the strength of the stimulus 

 and the length of the injured tract. The change in the period 

 of the excitatory wave is localised in the part of the nerve 

 that is affected ; while the diminution in the current of action, 

 once set up, affects the normal parts of the nerve as well. 

 The increase in the galvanometer deflection observed by Waller 

 as an after-effect depends not upon increased excitability, but 

 upon increased duration in time of the excitatory wave, which is 

 due to delay in the process of recovery. 



The negative variation depends not only upon the intensity of 

 the stimulus but also upon the strength of the current of rest led 

 off to the galvanometer. It is more vigorous, as the anode is 



