534 



NERVE. 



iwmm 



If the results are portrayed diagrammatically in a curve whose 

 abscissae represent units of intensity of stimulus, whilst the ordinates 

 represent those of galvanometric deflection, it will be seen that the 

 curve has three portions (Fig. 272). The first portion, when the 

 stimulating intensity is inadequate to evoke muscular response, is 

 slightly convex to the abscissae, i.e., the effect increases with increasing 

 increments in the exciting agent. This is succeeded by a portion which 

 is an ascending straight line, the effect increasing in strict proportion 

 to increase in the stimulus. The final portion is slightly concave to 

 the abscissa, the effect increasing less and less in proportion to the 

 augmentation of the stimulus. 1 



T c mp erat u r e. n 

 warming the nerve up to 

 35 or 40 C., the duration 

 of electrical response is 

 much diminished ; on the 

 other hand, it becomes pro- 

 longed in nerves cooled to 

 5 C. The low tempera- 

 ture acts in two ways, it 

 retards propagation, and 

 it causes a slow rate of 

 development of the re- 

 sponse in any one portion 

 of nerve. The total result 

 is thus a marked increase 

 in the negative variation. 

 It is not clear whether 

 there is an alteration in 

 the electromotive force of 

 the response apart from this 



FIG. 273. Effect of ether upon the electrical response change in its time relations. 

 of nerve. The upper tracing shows the increased 

 response after slight etherisation during period 



Before 



T] in fl uence O f 

 J 



., . j j 



marked EL ; the lower tracing shows temporary ttietw gases and drugs. 

 abolition after more profound etherisation during These have been investi- 

 period marked EL The series reads from left to -afp^ i~. v Wallor in T vmpVi 

 right. In this and all similar figures the vertical te 



lines are the photographed deflections of a galvano- the same way as in the 

 meter needle. experiments just described. 



Negative variations are 



evoked by a series of induced currents, short periods of excitation being 

 alternated with longer periods of repose. The nerve with both its 

 galvanometric and exciting contacts lies in a small chamber, through 

 which the gas is passed, and any alteration in the responses is indicated 

 by a change in the photographic record of the galvanometric deflections. 2 

 Ether, when in very small amount, causes an augmentation in the 

 effects ; when a little more pronounced, a primary augmentation is suc- 

 ceeded by diminution and possibly by abolition ; when still stronger, the 

 primary augmentation is not seen, and there is complete abolition. All 

 these effects soon pass away if the ether is removed, and even in cases 

 where complete abolition has been produced, the deflections return to at 

 least their original value on the removal of the vapour (Fig. 273). 



Chloroform, when very weak, causes primary augmentation, but 



1 Waller, Brain, London, 1895, vol. xviii. p. 210. - Ibid., vol. xix. p. 43. 



