1869.] Dr. C. B. RadclifiVs Researches in Animal Electricity. 387 



there is some accidental heterogeneity in these electrodes. Still no serious 

 complication in the problem is introduced by the presence of this purely 

 accidental current ; for all that it does is to shift in one direction or the 

 other the point from which the electrotonic movements of the needle have 

 to be reckoned. Be this accidental current present or absent, indeed, the 

 degree and direction of the electrotonic movements of the needle remain the 

 same, and it is only the starting-point of the movement which is shifted. 



These, then, being the facts, it is difficult to regard the electrotonic phe- 

 nomena in nerve which are exhibited in the galvanometer as modifications 

 of the nerve- current. The nerve-current, if present, is undoubtedly modi- 

 fied, just as is the accidental current depending upon the heterogeneity of 

 the electrodes of the galvanometer to which attention has just been di- 

 rected ; but the essential workings in electrotonus must be deeper than the 

 nerve- current, deeper even than the nerve. It would seem, indeed, that 

 the nerve-curreut must in reality play as accidental a part in the pheno- 

 mena of electrotonus as does the current depending upon heterogeneity 

 in the electrodes of the galvanometer in the experiment in which gutta 

 percha or silk moistened with water is substituted for the nerve. It would 

 seem, indeed, that a given degree of resistance between the voltaic poles is 

 in reality all that is essential to the manifestation of the galvanometric phe- 

 nomena of electrotonus — a resistance sufficient to pen up free positive elec- 

 tricity at the positive pole and free negative electricity at the negative pole ; 

 and that the movements of the needle may be owing to the outflowing or 

 inflowing of this free electricity through the coil of the galvanometer from 

 or to the pole which happens to be nearest to the coil ; for it is found that 

 similar movements to those which happen in electrotonus are ivitnessed 

 when the part of the nerve acted upon ordinarily by the voltaic current is 

 charged alternately with positive and negative electricity from a friction- 

 machine. In an experiment on electrotonus, as commonly conducted, the 

 insulation of the circuits of the galvanometer and the battery is sufficient 

 to prevent any passage of the voltaic current proper into the coil, but it is 

 not sufficient to hem in electricity of a higher tension ; it is not sufficient 

 to prevent the flowing of a stream of free electricity from the positive pole, 

 and to the negative pole, of which stream apart may pass through the 

 coil of the galvanometer, and so act upon the needle. And hence the 

 movements of the needle of the galvanometer in anelectrotonus and cath- 

 electrotonus ; for the movement in anelectrotonus is only that which hap- 

 pens when free positive electricity is passed through the coil, and the move- 

 ment in cathelectrotonus is only that which happens when free negative 

 electricity is so passed. 



Instead of the activity of nerve being paralyzed in anelectrotonus and 

 exalted in cathelectrotonus, a very different conclusion appears to be ne- 

 cessary. Taking the prepared limbs of a frog, and placing the middle 

 portion of the connecting band of nerve belonging to them across the poles 

 of a voltaic battery of which the circuit is open, a drop of salt water is ap- 



