II.J 



RETINAL DELAY 



27 



relating to the above described typical positive response to light 

 that demand consideration. I will deal with them as briefly as 

 possible. In the first place, it is of no moment as regards the 

 response, whether the accidental current described in paragraph 

 13 happens to be positive or negative. Kiihne and Steiner, 

 who paid particular attention to the point, refer to the fact 

 under the heading, Law of Constant Alteration of Tension, and 

 describe it thus : 



" Reversed direction of the current of darkness (our accidental 

 current) is without influence upon the magnitude and character 

 of the photo-electrical variations, which reverse their signs." That 

 is to say, according to the German designation, that the response 

 of a positive current of darkness is in the same direction as that 



FlG. II. Frog's eyeball. Galvunometric record of the normal 

 response at beginning (a) and end (w) of illumination. '1 he delay in 

 each case is about i sec. ; that of the galvanometer is ^ sec. ; the net 

 retinal delay is therefore about ^ sec. 



current, or "positive," while the response of a negative current of 

 darkness is in the opposite direction to that current, or " negative." 

 I have preferred to this correct, but rather confusing mode of 

 description, to say that the response is normally from fundus to 

 cornea or positive^ whether it starts above or below the line of 



