158 RESEARCHES ON IRRITABILITY OF PLANTS 



oil, 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.' l 



In this experiment we have an instance of transmission 

 of excitation through heat-rigored animal tissue parallel to 

 Haberlandt's experiment on transmission through scalded 

 plant-tissue. In both these cases it is evident that the 

 scalded tissues, though under heat rigor, were not really 

 killed ; and that the induced block or abolition of con- 

 ductivity (caused by heat rigor, electrotonus, and so on) 

 is after all relative. There may thus be an effective physio- 

 logical block for normal intensities of stimulation, which 

 would, however, fail under abnormal intensities of stimulus 

 such as that of a burn or of a cut. In Kiihne's experiment 

 the intense excitation of scissors-cut failed to be arrested, 

 though the conductivity of the nerve had been depressed 

 under heat-rigor. Similar considerations will explain how 

 the intense excitation caused by a burn or a cut may be 

 transmitted through the narcotised or scalded areas in 

 Mimosa. 



The experiment of Kiihne shows further that the conduc- 

 tivity may persist even after the abolition of the motile 

 excitability. The rigored muscle is seen to have lost its 

 motility, though the embedded nerve retained a certain 

 amount of conductivity for excessively strong stimulus of 

 a cut. 



In turning our attention to Kiihne's experiment we realise 

 the error involved in ignoring the factor of intensity of 

 stimulus in the matter of the effectiveness of a given block to 

 the transmission of excitation. The necessity of discarding 

 crude and drastic methods of excitation in researches on 

 variation of conductivity will now have become obvious. 

 The object of our inquiry is not to find whether a violent 



1 Biedermann : Electro-physiology, vol. ii. p. 57 (Macmillan). 



