1877.] 



Excitability of Motor Nerves, 



217 



stimulation. It is the averages so obtained which are rendered in the 

 following tabular statement of results 





Anodic make. 



Kathodic make. 





•00533 sec. 

 •00311 sec. 



•00439 sec. 

 •00117 sec. 



Concerning these results it is only necessary to observe that there is a 

 tolerably close parallel between them and those which were previously 

 obtained by employing stimuli of minimal intensity. That is to say, in 

 the case of the anodic make the increase of excitability due to injury is, 

 roughly estimated, in the proportion of about 3 : 5, and this ivheiher such 

 increase is estimated by employing stimuli of graduated intensity, or stimuli 

 of graduated duration ; and similarly in the case of kathodic make, 

 though the proportions here yielded by the two methods are not quite so 

 equal as in the other case. But this general parallelism between the 

 quantitative results yielded by the two methods in the case of both the 

 closing excitations serves but to render more conspicuous the difference 

 in the results yielded by the two methods in the case of the anodic opening 

 excitation ; for while in the first of the two methods, viz. that in which 

 stimuli of minimal intensity were employed, it was found that after injury 

 the excitability of a nerve towards the anodic-break stimulus is greater 

 than it is towards the anodic-make stimulus, such is not found to be the 

 case when, as in the second of the two methods, these two stimuli are 

 made to follow one another in very rapid succession. I can only explain 

 this fact by supposing that, for the breaking excitation to be fully effec- 

 tual, a certain interval of time is required for the nerve to become 

 polarized by the passage of the voltaic current ; and, therefore, that, in my 

 experiments with currents of minimal duration, a response to the anodic 

 make was always given when a shorter duration of the current was em- 

 ployed than that which was required to produce a response to the anodic 

 break*. 



§ 4. In conclusion, I may state that the period of latent stimulation 

 does not appear to be perceptibly affected by nerve-injury. 



* How much shorter I was not able to ascertain, from the fact that the contraction 

 due to the make and that due to the break, when they both occur together, become so 

 blended that the eye is not able to analyze them with sufficient precision to decide at 

 what point the anodic-break contraction first asserts itself. Hence we must rest satis- 

 fied with the general statement, that the minimal anodic-break stimulus is in some un- 

 known degree of longer duration than the minimal anodic-make stimulus ; and this 

 even after the susceptibility of the nerve to the former stimulus is so enormously aug- 

 mented by injury as, from the other method of experimentation, we know it to be. 



