9 6 



COMPARATIVE ELECTRO-PHYSIOLOGY 



under continuous stimulation in the petiole of celery. The 

 fatigue in the mechanical response of muscle under similar 

 conditions is given in a for the purpose of comparison. The 

 effect of rest in inducing molecular recovery, and hence in 

 the removal of fatigue, is illustrated in the following set of 

 photographic records (fig. 66). The first of these shows the 

 curve of electrical response, obtained with a fresh plant. It 

 will be seen that under a continuous stimulation of two minutes 

 the response first attains 

 a large amplitude, after 

 which it declines, in a 

 fatigue-reversal. Another 

 two minutes were now 



FIG. 64. Rapid Fatigue under Con- 

 tinuous Stimulation in (a) Muscle ; 

 (b] Leaf-stalk of Celery (Electrical 

 Response) 



FlG. 65. Photographic Records of 

 Normal Mechanical Response of 

 Mimosa to Single Stimulus (upper 

 figure), and to Continuous Stimu- 

 lation (lower figure) 



In the latter case the leaf is erected in 

 spite of continuous stimulation. 



allowed for recovery, and we observe that a partial recovery 

 takes place. Stimulation was now repeated throughout 

 the succeeding two. minutes, to be followed once more by 

 two minutes' rest. The response in this case is seen to be 

 decidedly smaller than at first. The same effects are seen 

 in the third response. A period of rest of five minutes was 

 next given, and the curve subsequently obtained under the 



