THE KILLIFISH 



27 



as a temporary reactivation of the original fibers with 

 a corresponding response of the melanophores. When 

 these fibers were originally cut they were not paralyzed 

 by this operation, but were profoundly stimulated, and 

 this stimulation continued, though with diminishing 

 energy, for one or more days as indicated by the state 

 of their effector organs, the melanophores. This at least 

 is the interpretation that I 

 have been led to put on this 

 phenomenon. I am fully aware 

 that it is quite contrary to the 

 teachings of conventional neuro- 

 physiology. But this type of 

 physiology has been developed 

 on the basis of the nerve- 

 muscle preparation, and there 

 may be important differences 

 between such preparations 

 and those based on melano- 

 phores. 



If cut melanophoral nerve- 

 fibers remain active for a long 

 time after severance, there must 

 be a continuous flow of activa- 

 ting impulses from the region of 

 the cut to the melanophores 

 that constitute the dark band. 



One test of the correctness of this view would be to 

 attempt to block such a flow. This cannot well be done 

 with drugs because of the readiness with which they 

 diffuse, but it can be accomplished by the application of 

 cold. If a sharply bent, capillary glass-tube carrying 

 a chilled mixture of water and alcohol several degrees 

 below zero centigrade is applied to a region on a fully 

 formed caudal band about midway its length, a very 



Fig. 21. Diagram of 

 a fully formed band in 

 the tail of a killiflsh to 

 which a cold block {A) 

 had been applied with 

 the result that the distal 

 half of the band faded 

 in about a quarter to 

 half an hour after the 

 application of the block. 

 Parker, Pro. Nat. J cad. 

 Set., 1934,20, 309, fig. 5. 



