130 



PHYSIOLOGY OF MUSCLES AND NERVES. 



indicate the change which the excitability undergoes at 

 any definite point in the nerve, let us suppose a straight 

 line drawn at this point at right angles to the longitu- 

 dinal direction of the nerve, and let this line be made 

 longer in proportion as the change is greater. In order, 

 moreover, to show that the changes which occur toward 

 the anode are of an opposite tendency to those toward 

 the kathode, let the line on the anode side be drawn 

 downw^ard, that on the kathode upward. By connecting 

 together the heads of these lines a curve is obtained 

 which diagrammatically represents the changes at each 



Fig. 31. Electrotonus under the influence of currents of 



varying strength. 



point. Of the three curves, the middle represents the 

 condition under the influence of a current of medium 

 strength ; the other two curves, indicated, the one by 

 short lines, the other by a dotted line, represent the 

 conditions under the influence of a strong and of a 

 weak current respectively. These curves show that the 

 changes are more marked in proportion as the cur- 

 rent is stronger ; that they are most strongly developed 

 exactly at the electrode points ; and, finally, that the 

 neutral point, under the influence of currents of dif- 

 ferent degrees of strength, assumes a variable position 

 between the electrodes. 



