EFFERENT FIBERS OF THE OPTIC XERVE 229 



optic nerve of one eye was exposed and stimulated for 1\ hours, in the 

 light, with a weak current from an induct orium. Inspection of the 

 two retinas showed that the pigment in the eye that had licen elec- 

 trically stimulated was uniformly expanded (fig. 2), while in the control 

 eye the pigment still remained contracted as is characteristic of dark 

 adaption (fig. 3). 



Since repeated trials confinned these results, the conclusion 

 follows that there must be nen'ous elements of an efferent nature 

 in the optic nerve of this fish which nonnally receive unpulses 

 from the central nervous system, and can be made to function 

 experimentally by electrical stimulation. The result in either 

 case is a release from an inhibition exerted upon the pigment cells 

 by a mechanism possibly involving the autonomic fibers from the 

 ciliar\' ganglion. 



Previous oxperijuentation (Arey, '16) has sliown tlial botli in 

 light and in darkness the retinal pigment of fishes is more highly 

 expanded at low temperature (0°(\ +) than at high temperatures 

 (25°C. ±), hence a series of experiments was next made to discover 

 whether after the optic nerve was cut temperature woiUd still 

 be efficient in producing the characteristic temjierature res]K)nses. 

 In detenninations jnade l)oth in light and in darkness, the results 

 were identical with those found in normal animals, for at r>°Q\, 

 the expansion of ])igiiK'iit was greater tlian at 2')"(\ (figs. 1 and 

 2; 3 and 4). 



In order to ])r()du{'e slunp contrasts (in the light at least), 

 before the optic nerA'e was cut, a preUminaiy treatment at a 

 tem])eratiu'e of o°C. was necessaiy. If the i:)relijninan' treat- 

 ment was at 25°C. the pigment remained in the ])osition charac- 

 teristic of that temperature, regardless of the temperature that 

 followed. From this result additional evidence is obtained, over 

 that already advanced (Arey, '16), to show that a high tempera- 

 ture is more efficient in causing positional changes of the retinal 

 pigment than is a low temi^eratiu'e, and that temperatiu'e is 

 more efficient than either light or darkness." 



* It shoulil be reinLMnl:)ercHl, however, that temperature merely produces a 

 quantitative redistribution of the already expanded or contracted pigment, the 

 extent of its influence always being limited in this way. 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 26, NO. 3 



