REVIEW OF RESPONSE OF ISOTROPIC ORGANS 691 



by fatigue was shown in tungsten under electric radiation, 

 while in the contractile response of indiarubber under thermal 

 stimulation it took place with intermediate diphasic (fig. 

 397). The characteristic curve has been shown to exhibit 

 the history of molecular transformation under continuous 

 stimulation. In the first part of this curve a progressive 

 change is shown to be manifested outwardly by increasing 

 contraction or galvanometric negativity. In the second part 

 a reversal of this process is seen to occur. This is illustrated 

 in records of response under continuous stimulation. Thus 

 muscle shows increasing contraction, to be followed by 

 fatigue-relaxation (fig. 64). The same thing is observed in 

 Mimosa, as a fall of the leaf, followed by its re-erection 

 .(fig. 65). Electrically, this is observed as increasing galvano- 

 metric negativity, followed by reversal to positivity. These 

 phasic alternations may in some cases be exhibited only 

 once, and in others repeatedly. Thus, in a certain style of 

 Datura such phasic alternation is seen to occur twice (fig. 

 76) ; and again, in leaflets of Desmodium gyrans, at first 

 quiescent, continuous stimulus of light gives rise to those 

 repeated alternations of negative and positive which consti- 

 tute multiple response (fig. 141). The distinction between 

 the tissue which gives only one such alternation, and others 

 which display it in repeated succession, is not, it should be 

 borne in mind, rigid. Even skeletal muscle, under certain 

 circumstances, is found to give rise to rhythmic excitations. 

 The fact that multiple response is a phenomenon of wide- 

 spread occurrence, and not specifically characteristic of any 

 particular kind of tissue, has been fully demonstrated in the 

 course of the present work. 



It would appear that there is a tendency of the incident 

 stimulus, when applied continuously, to find an expression 

 whose predominant characteristics are alternating. We may 

 first have the exhibition of excitatory molecular distortion. 

 But when this has reached a maximum, no further excitatory 

 expression being possible, the incident energy becomes 

 relatively effective in increasing the internal factor, with 



Y Y 2 



