1882.] Excitability of Sensory Nerves of Man. 369 



Strength, of kathodic 

 polarisation. 



Variations of excitability of sensory nerves 

 expressed in terms of distance of secondary coil. 



Ditto, of 

 motor 

 nerves. 



1. 



2. 



3. 



4. 



5. 



6. 



7. 



8. 



9. 



10. 



a. 



b. 



o 



100 



107 



110 



122 



127 



110 



127 



100 



104 



115 



116 



113 



Weak, 5 — 10 cells . . 



142 



115 



118 



128 



133 



120 



133 



115 



148 



130 



127 



118 



Stronger, 10— 20 cells 



160 



120 



124 



136 



139 



126 



139 



122 



166 



141 



153 



137 



The number of cells given for the polarising current were those 

 used when no resistance was added. In some of the experiments 

 10,000 ohms were thrown in, and a proportional increase in the 

 number of cells became necessary (viz., about eight times as many as 

 in the former instances) : — 



2. The effect of induction shocks is at first diminished, then in- 

 creases to normal, or above normal, when the excitation falls upon the 

 anodic zone of the polarising current. We suppose this effect, which 

 is the same as that observed on the motor nerve, to be due to an 

 invasion of the anelectrotonic by the katelectrotonic influence when 

 the polarising current is increased beyond a certain strength. This 

 invasion takes place more readily from the polar into the peripolar 

 zone, than in the opposite sense. 



Xumber of cells of poO 







2 



4 



6 



8 



10 



12 



14 



16 



18 



20 



22 



24 



30 



40 



Distance of se- fPeri - \ 

 condary coil polar j 

 necessary to < 



102 



92 



88 



86 



87 



92 



95 



101 



104 



107 



111 



114 



116 







produce mini- 

 mal sensation.. l^Polar ... 



115 











85 











75 







80 



85 



This experiment was made upon the cutaneous nerves of the back 

 of the arm, the other plate resting on the leg. The galvanometer 

 showed that the variations in the effect were unaccompanied by any 

 changes in the resistances in circuit. 



With reference to the after-effects of which the accurate deter- 

 mination offers considerable difficulties, we content ourselves with 

 stating here that they appear to consist in an increase of excitability 

 both after anodic and kathodic influence, preceded in the latter case 

 by a short but appreciable diminution when the polarisation has been 

 long and strong enough. 



