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COMPARATIVE ELECTRO-PHYSIOLOGY 



excitability. It will thus be seen that even when the funda- 

 mental excitatory reaction is instantaneous, its outward 

 expression, whether mechanical or electrical, may nevertheless 

 appear to be subject to delay in consequence of the inertia 

 of the particular indicator concerned. 



As regards these two forms of response, it should further 

 be remembered that the mechanical and electrical responses 

 are independent indications of the fundamental excitatory 



reaction, and that neither is 

 dependent for its occurrence 

 on the other. Thus, when 

 the mechanical response is 

 physically restrained, the 

 electrical response takes 

 place unimpeded. I shall 

 here relate an experiment 

 in illustration of this point 



A leaf of Mimosa re- 

 sponds to strong stimulus 

 by complete collapse, and 

 the recovery from this state 

 is somewhat prolonged, 

 taking from five to eighteen 

 minutes, according to the 

 season. In order to obtain 

 a series of responses with 

 these recoveries, within a 

 reasonable time, I find that 

 it is necessary to apply 



moderate stimulus. There is then a moderate fall, without 

 complete collapse, and recovery under such circumstances is 

 found to take place within a minute or so. In order to show 

 that electrical response takes place, even when the leaf is 

 prevented from giving mechanical expression, I held the 

 petiole in a clamp, and obtained the set of electrical responses 

 seen in fig. 14. The first series of this record were taken 

 in answer to uniform stimuli of a given intensity, and the 



FIG. 14. Photographic record of Elec- 

 trical Response by Galvanometric 

 Negativity of Pulvinus of Mimosa, 

 when leaf is physically restrained from 

 falling. The first series in response to 

 given uniform stimuli ; the second 

 series to stimuli twice as strong. 



