VARIOUS TYPES OF RESPONSE 



99 



In connection with this subject of phasic alternation I 

 may describe a certain curious phenomenon, which 1 have 

 often noticed ; I refer to the periodic waxing and waning of 

 both mechanical and electrical responses. The simplest 

 example of this will be a case in which the responses are 

 alternately large and small. But others are to be found in 

 which the groupings are more complex. In fig. 68 a is seen 

 such a simple alternation, in the electrical response of the 

 petiole of cauliflower, under successive uniform stimuli. In 



$, c, and d are shown similar alter- 

 nations in multiple and autonomous 

 responses. I give also a photographic 

 record (fig. 69) of a similar alterna- 

 tion in the automatic pulsations of 

 the leaflet of Desmodium gyrans. 



FIG. 69. Photographic 

 Record of Periodic 

 Fatigue in the Auto- 

 matic Pulsation of Des- 

 modiuin gyrans 



FIG. 70. Periodic Fatigue in 

 Pulsation of Frog's Heart 

 (Pembrey and Phillips) 



Similar alternations are sometimes observed in the beating 

 of frog's heart (fig. 70). 



In the following record of mechanical response (fig. 71), 

 taken from the style of Datura alba, we find that fatigue, as 

 already understood, would not explain the phenomenon 

 observed. For here, under the continuous action of stimulus, 

 without any intervening period of rest for the so-called 

 ' assimilatory ' recuperation, we see that a second response 

 occurs. I shall later give other instances in which pulsating 

 responses, with their alternating negative and positive phases, 

 are given, under the action of continuous stimulation. We 

 pass here imperceptibly from the ordinary phenomenon of 



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