VASODILATATION DUE TO A COLOR STIMULUS. 2Og 



were maximally expanded. An intra-peritoneal injection of 0.50 

 to 0.75 cc: of adrenalin chloride dilution I to 1000 was then 

 given. In about 30 seconds a contraction of the melanophores 

 was noticeable and this contraction, as judged by the unaided 

 eye, was completed in about two minutes, when the fish assumed 

 a pale grayish hue. In two to three minutes it began to assume 

 a yellowish color, due to the partially contracted xanthophores 

 in which a dense orange concentration of pigment might be seen 

 on microscopic examination. In three to four minutes, a dilata- 

 tion of blood vessels was noticeable at the base of the fins, 

 especially the dorsal fin and about the head. The dilatation 

 extended over the body generally within five or six minutes. 

 In about twelve to fifteen minutes the coloration was similar to 

 that obtained under the influence of a red environment, except 

 that the adrenalin caused a more pronounced dilatation in 

 specific regions as for example in the fins. The yellow color 

 gradually diminished, but the vasodilatation persisted for hours. 

 In one specimen the maximum degree of dilatation was observed 

 five hours after the injection of adrenalin. The time periods for 

 the different phases of the reaction varied slightly according to 

 size and vigor of the fishes and the amount of adrenalin chloride 

 injected. But those given above are typical of a dozen experi- 

 ments on specimens 7 to 8 cm. in length. 



If the caudal fin be examined under the microscope when the 

 injection is made, it will be seen that there is an immediate 

 constriction of the blood vessels causing a stoppage of circulation. 

 This is soon followed by a renewal of the circulation which 

 gradually extends over the fin. Adrenalin causes an immediate 

 constriction and a post-dilatation of the blood vessels in Fundulns 

 as in human beings. Apart from giving a convenient control 

 for experimentation this post-dilatation effect of adrenalin is 

 itself an interesting phenomenon in the light of a similar effect 

 produced by a red environment. 



