182 



S. R. DETWILER 



When a constant current is passed through the tortoise eye 

 much more definite and pronounced effects are obtained than 

 with an induced current. The eyes, after being removed, were 

 placed in a long trough containing tap-water to which a little 

 salt solution had been added. The current (15-20 M. A.) was 

 then passed from one end to the other and for from 15 to 30 

 minutes. Both light and dark eyes were again used and the 

 current in some was passed from the posterior to the anterior 

 of the eye (centrifugal), and in others, in the opposie direction 

 (centripetal) . 



The examination of sections of eyes treated in this way show 

 that in all cases a migration of the pigment takes place (fig. 5). 

 This represents a typical case and in table 4 are given the aver- 

 age of a series of measurements. 



^ Based on 10 measurements. 



A current which has been passed through the eye for 15 min- 

 utes is as effective as one which was allowed to pass for 30 

 minutes and presumably weaker currents of shorter duration 

 would give the same results. In a few cases the retinae through 

 which the currents had been passed for thirty minutes showed 

 a partial breaking and tearing apart, particularly of the inner 

 and outer nuclear layers. 



The effects of a constant current on the cones is also very 

 striking. Again the cones are much broader than normally, 

 but instead of being contracted as after stimulation with the 

 induced current they are much elongated (fig. 11, and table 4). 

 The cone nuclei are not usually affected in any constant way 



