CONDUCTIVITY AND EXCITAHILITV 223 



later (p. 245), which shows that in that case, under moderate 

 fatigue, conductivity was diminished by 18 per cent, of its 

 normal value. 



The following experiments give us a further and striking 

 demonstration of the diminution or abolition of conductivity 

 under fatigue. If we take a leaf of Mimosa, and excite it, by 

 snipping off a terminal leaflet, borne on one of the four sub- 

 petioles, the stimulus, transmitted along the narrow con- 

 ducting channel of that sub-petiole, and passing through the 

 large channel of the petiole, will, on reaching the pulvinus, 

 cause the fall of the leaf After a suitable period of rest, 

 the leaf will re-erect itself If now the operation be several 

 times repeated, by stimulating the same sub-petiole, it will 

 be found eventually that the leaf no longer responds. That 

 this is due to the fatigue in conductivity of the sub-petiole 

 may be proved, by snipping a leaflet off a second sub- 

 petiole, which will be found to conduct the stimulus, and 

 produce depression of the leaf, as did the first sub-petiole 

 when fresh. It will be noticed here that the excitation which 

 abolished the conductivity of the first sub-peciole, did not 

 abolish that of the main petiole. This is due to the fact that 

 the somewhat enfeebled stimulus on reaching the petiole is 

 spread over a larger channel, and therefore the strain-effect 

 which it produces there is relatively much less. 



id) By effect of ancEsthetics. — We shall now study the effect 

 of anaesthetics on conductivity. This may be shown by the 

 local application of ether to the petiole, in the intermediate 

 portion of a BiopJiytmii leaf, beyond, say, the first three pairs 

 of leaflets. Stimulus applied below this area will be con- 

 ducted to it, as seen by the fall of intervening leaflets, but its 

 further passage will be blocked, and neither the leaflets of 

 the etherised area, nor those beyond, will show response. 

 That this abolition of conductivity, however, is only tempo- 

 rary, is seen when the stimulus is repeated after blowing off 

 the ether vapour. All the leaflets, from first to last, will now 

 be found to respond. If etherisation, however, be carried 

 too far, the abolition of conductivity persists for a long time. 



