L.— THE AFTER-EFFECT OF LIGHT 



By 



Sir J. C. BosE, 



Assisted by 



SuRENDRA Chandra Das. 



We have considered two types of diurnal movement, 

 one due to the predominant action of variation of light, 

 and the other, to that of changing temperature. There 

 are, however, other organs which are sensitive to variations 

 both of light and of temperature. The effect of light is, 

 generally speaking, antagonistic to that of rise of tempera- 

 ture ; hence the resultant of the two becomes highly 

 complex. 



Still greater complexity is introduced by the different 

 factors of immediate and after-effect of light. This latter 

 phenomenon is very obscure, and I attempted to determine 

 its characteristics by electrical method of investigation. A 

 fuller account of after-effect of light on the response of 

 various plant-organs and of animal retinae will be found 

 elsewhere.* I shall here refer only to one or two 

 characteristic results which have immediate bearing on 

 the present subject. 



Direct stimulation under light induces excitatory reac- 

 tion, which is mechanically exhibited by contraction, and 

 electrically by induced galvanometric negativity. Under 

 continuous stimulation, the excitatory effect, either of posi- 

 tive curvature or of induced galvanometric negativity, is 

 found to attain a maximum. This is often found to 

 undergo a decline and reversal ; for under continuous 



* " Comparative Electro-Physiology " — p. 392. 



41 A 



