EFFECT OF LIGHT ON THE RETINA 183 



and are either round or oval as is ordinarily the case. In a few 

 cases however they seem to be broken down and drawn out 

 and up into the myoid (fig. 5). 



It has been known for some time that the melanophores of 

 the skin in many animals are caused to contract when stimu- 

 lated with an induced current and to expand when stimulated 

 with a constant current (Laurens '15, p. 609). It would seem 

 that the same is true of the pigment cells of the retinal epithelium. 





Fig. 5 A portion of the retina of Chelopus insculptus showing the effects of 

 passing a constant current of 18 M. A. for a period of 15 minutes through the 

 eye. (Current passing from the cornea towards the optic nerve). 



In all four cases in which the current was passed from the 

 cornea to the optic nerve the pigment cell nuclei were changed 

 in shape and position (fig. 5). Instead of being roundly oval 

 with the long axis parallel to the choroidal limit of the cell, they 

 are narrowed and lengthened and with the long axis at right 

 angles to the usual position. This condition of affairs was never 

 found when the current was passed in the opposite direction 

 and would seem to indicate a polar effect of the current. 



