236 LESLIE R. AUEY 



fisli, it would seem reasonable to expect that the same would 

 occur in darkness, provided efferent impulses in the optic nerve 

 directly stimidate the i-etijial elements to undergo positional 

 changes. 



CJertz ('11) tested the effect of electrical stimulation for one to 

 two minutes in dai'kness and in light upon the eyes of Abramis 

 brama, both excised and in vivo, but only negative results were 

 obtained. Englemann ('85) had previously asserted that the 

 cones and retinal pigment of the excised or normal eyes of dark- 

 adapted frogs responded to induction shocks in a similar way 

 as to light, and Arcoleo ('90) also claimed to have observed 

 pigment migration under these conditions in a pithed toad and 

 frog, as well as upon dark adapted excised eyes. The more 

 recent work of Lederer ('08) and of Fujita ('11) upon normal 

 frogs nevertheless, has not supported this view. 



When the cut stump of the optic nerve of a dark-adapted 

 Ameiurus was stimulated with a faradic current in total dark- 

 ness, no distinct changes occurred in the retinal pigment or rod 

 cells, even though the stimulation continued for 45 minutes. Sim- 

 ilar treatment of excised eyes also gave negative results. These 

 observations indicate that a satisfactory explanation of the action 

 of the efferent nerve fibers must be sought by viewing the situa- 

 tion in a different way. 



It is instructive to adopt the point of view suggested by a 

 study of the vasomotor nerves. In this case a tonic condition 

 is presupposed either through the action of vasoconstrictor nerve 

 fibers or possibly by the intrinsic properties of the muscles 

 themselves. Dilation is believed to be accomplished by the 

 action of dilator nerve fibers, whose impulses inhibit the tonic 

 contraction of the musculature, thus indirectly causing relaxa- 

 tion. To work out a detailed application for the condition found 

 in Ameiurus would be both unprofitable and unwarranted. The 

 simplest conception is that impulses^ from the efferent compo- 



* This view of tonicity differs greatly from that which Herzog ('05) believed 

 to exist in the frog. His statement that after destruction of the central nervous 

 system the pigment and cones gave abnormally vigorous responses in the dark, 

 as if released from an inhibition, does not agree with the observations of Ham- 

 burger ('89), Arcoleo ('90), Dittler ('07) and Garten ('07). 



