REACTION OF MOTOR NERVES TO DIRECT STIMULATION. 595 



at its height, to a point midway between the poles, where the two electrotonic re- 

 gions meet, and where the charge is at zero. 



FIG. 205. 



i 



_n 



U 



III 



And as in this case so in that in which a galvanoscopie frog is arranged and ex- 

 amined in the same manner as that in which the nerve was arranged and examined 

 in the last experiment, for (as is shown in the same way in the next figure) it is 

 found that the two corresponding halves of the frog and of the nerve, are in pre- 

 cisely the same predicament as to charge: thus- 



Fit;. 206. 



_j 



On the other hand, if a wire be made to take the place of the nerve or galvano- 

 scopie frog, all these evidences of charge are wanting, unless it be that there is some 

 impediment to the free passage of the current between the poles, from insufficient 

 contact with the poles, from want of conductive capacity in the wire, or from some 

 other cause. 



These then are the facts. Movements of the needle, like those belonging to elec- 

 trotonus, are caused by the passage of free Franklinic electricity through the coil. 

 There is an outflow of free electricity from the voltaic poles in the case where electro- 

 tonic movements of the needle are present. There is no such outflow when these 

 movements are absent. And so it may be that the electrotonic movements of the 

 needle which are observed when the electrodes of the galvanometer are placed any- 

 where (not on the nerve merely) in the course of this outflow, are nothing more than 

 the natural consequences of the passage of free electricity into the coil from the vol- 

 taic pole which happens to be nearest to it; the free electricity passing through the 

 coil from one electrode of the galvanometer to the other (from that which is nearest 

 to the voltaic pole to that which is furthest from the pole), rather than directly along 

 the nerve from one electrode to the other, for the simple reason that it meets with 

 less resistance in the coil than in the nerve. It cannot well be otherwise, for it is 

 not to be supposed that the outflow of free electricity in this case should not act upon 

 the needle in the very same way as that in which the outflow of free electricity from 

 a frictional machine has been seen to act. 



(b) In order to be sure as to the facts with which he has to do in the next place, 

 Dr. Radcliffe employs two methods of inquiry. 



The first method is that which is carried out more simply than the second, but it 

 is less exhaustive. In it a galvanoscopie frog is arranged upon a plate of paraffin 

 with its two limbs stretched out in opposite directions, and with the two exposed 

 nerves resting at their middle, as in the last figure, upon the two voltaic poles, and 

 then a state of slight tetanus is set up in both the limbs simultaneously by applying a 

 drop of strong solution of salt to the nerve on each side where it lies beyond the pole, 

 or else by faradizing with very feeble currents at the same spot. Until the limbs 

 are slightly tetanized the voltaic circuit is open, and there is consequently no electro- 

 tonus; when the limbs are slightly tetanized, the voltaic circuit is closed, first with 



