CHARACTER OF TRANSMITTED IMPULSE 157 



It is also extremely doubtful whether in the particular 

 experiment with Mimosa the conducting-tissue in the in- 

 terior could have been effectively narcotised by the external 

 application of the anaesthetic. The task would almost 

 be as difficult as narcotising a nerve-trunk lying between 

 muscles, by the application of chloroform on the skin out- 

 side ! In the case of the plant it is conceivable that after a 

 very long application a small quantity of narcotic may, by 

 absorption, get access to the internal conducting-tissue ; 

 but narcotisation in these circumstances can only be partial. 

 In such a case the transmitted effect of a feeble or a moderate 

 stimulus will alone be arrested ; but the block will fail to 

 arrest the transmitted effect of intense stimulation. These 

 considerations will probably explain Pfeffer's observation 

 that, while the effect of strong injury stimulus was always 

 transmitted across the narcotised area, a moderate mecha- 

 nical stimulus was but occasionally transmitted. 



In Haberlandt's experiment the conducting-tissue was 

 supposed to have been killed by scalding. If this had really 

 been the case, then it may be supposed that under an 

 exceptionally strong stimulus a hydrostatic disturbance had 

 been transmitted through the dead tissue and caused 

 stimulation of the distant leaf, as a mechanical blow de 

 novo. But excitatory transmission in a plant is usually 

 accomplished by a stimulus which is feeble. Strong doubt 

 may also be entertained as to whether the tissue had really 

 been killed. In my own experience I find it extremely 

 difficult to be sure of killing the interior of a tissue by 

 scalding the outside. This derives additional support from 

 certain experiments of Kuhne on conduction of excitation 

 in a nerve, the specimen employed being the sartorius of 

 a frog. 



' 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 bifurcation branch many 

 times dichotomously. When Kuhne threw the broad upper 

 end of the muscle into heat rigor by dipping it into warm 



