COLOR CHANGES IN ANIMALS 



remarkable occurrence will be noticed. The band prox- 

 imal to the region of the application of the cold tube 

 will remain unchanged, but that distal to it will in the 

 course of half an hour or less gradually fade out (Fig. 

 21). This is what would be expected if the band was 

 maintained by a continuous flow 

 of impulses from the cut toward 

 the free edge of the tail. 



A cold block may be used in 

 still another way to test this 

 question. If the cold tube is 

 applied to a spot near the center 

 of the tail of Fundulus and a 

 denervating cut is made some 

 distance proximal to the region 

 of application, a dark band will 

 begin to form and will extend 

 from the cut to the region of 

 the cold block but, as might 

 be expected, will not pass be- 

 yond this block. If now a cut 

 is made immediately distal to 

 the block and in line with 

 the first one, an additional 

 band will form from the new 

 cut to the edge of the fin (Fig. 

 2.2). From this experiment two 

 important conclusions may be 

 drawn: first, that cold in the neighborhood of o° C. 

 serves as a real block to nervous impulses over chro- 

 matophoral fibers; and, second, that what is transmitted 

 from the central organs over these fibers is not an inhibi- 

 tory influence that is checked when the fibers are cut, 

 but a true activating influence that may be excited 

 locally by severing the nerve. 



Fig. 22. Diagram of 

 a caudal fin of a killifish 

 across a part of which a 

 capillary tube {A) carry- 

 ing a chilling mixture 

 was placed. The cut (B) 

 was followed by the for- 

 mation of a dark band 

 which reached from the 

 cut to the chilled area 

 but did not enter it. The 

 cut (C) gave rise to a 

 dark band which reached 

 to the edge of the tail. 

 Parker, Pro. Nat. Acad. 

 Set., 1934, 20, 307, fig. 2. 



