VIII 



CONDUCTIVITY AND EXCITABILITY OF NERVE 



57 



glossal nerve, we may refer to the recent repetition by Kochs (1 0) of 

 Paul Bert's experiment, in which the exposed tip of a rat's tail was 

 grafted on to the skin of the back, and then cut off at its original 

 attachment after the wound had healed up. After a short time 

 sensibility is restored in the transplanted tail, apparently indicat- 

 ing that the not yet degenerated nerves were able to conduct 

 excitation in a direction opposed to the normal. These experi- 

 ments were, however, shown by Kochs to be quite inconclusive. 



On the other hand (apart from certain observations of du Bois- 

 Eeymond on the transmission of the negative variation in both 

 directions), we must reckon as 

 genuine experimental evidence 

 for the double conductivity of 

 nerve, the experiments on 

 branching nerve -fibres, under- 

 . taken by Kiihne (11) in the 

 in tra- muscular nerve -branches 

 of different frog's muscles, e.g. 

 sartorius and gracilis ; by Ba- 

 buchin in the still more suitable 

 organ of Malapterurus. The 

 delicate nerve, which enters the 

 middle of the sartorius by one 

 side, divides within the muscle, 

 so that the single fibres that 

 constitute the bifurcations branch many times dichotomously. 

 When Kiihne threw the broad upper end of the muscle 

 into heat-rigor by dipping it into warm oil (Fig. 160 ), the 

 half which remained normal twitched on cutting the rigored 

 portion with scissors, showing that excitable nerve-fibres could 

 still be mechanically excited between the rigored and dead 

 muscle - fibres, and thus carry the excitation centripetally 

 into branches which divide above the rigored portion of the 

 muscle. Still more convincing is the so-called " bifurcate experi- 

 ment," in which the broad end of the sartorius is split up length- 

 ways, when excitation of one fork nearly always produces an 

 accompanying twitch in the other (Fig. 160 6). Since any propa- 

 gation by secondary excitation from fibre to fibre seems to be 

 excluded in normal muscles, the only possible interpretation is 

 that one twig of the branched nerve which supplies both forks 



FIG. 160. 



