LOCAL PHOTIC STIMULATION 



159 



My investigations relate to the effects not only of photic 

 but also of other modes of stimulation, the results being 

 essentially similar in all cases. I shall first deal with the 

 effect of photic stimulation, for which special means have 

 to be devised for the local application of stimulus of feeble 

 and of strong intensity. 



Local Application of Photic Stimulus 



Feeble or moderate stimulation. — -This is secured by a 

 device consisting of an 'incandescent 4-5-volt pea-lamp 

 placed at one end of a tube, the other end of which is pro- 

 vided with a focusing lens L. The incandescent filament 

 is adjusted horizontally, so that a sharp line of light can be 



Fig. 87. The incandescent electric lamp-holder. A line of light 

 can be directed vertically downwards on to the upper half, or 

 vertically upwards on to the lower half, of the pulvinus. 



thrown across the middle of either the upper or lower half 

 of the pulvinus. The lamp-holder can be raised or lowered ; 

 it can be inclined vertically downwards or upwards for the 

 specific purpose of the experiment (fig. d)y). 



Strong stimulation. — The source of light is a self-feeding 

 small arc-lamp which maintains approximately constant 

 light. The focusing lens gives a horizontal and slightly 

 convergent beam of light ; this is thrown vertically either 



