CHEMICAL AGENTS ON CHROMATOPHORES 173 



and twenty-six hours. There is no convulsive period. In a 

 weak solution of 0.025 per cent of pictoroxin the contraction is 

 slightly less rapid, and lasts indefinitely (fig. 11). 



When the tail is cut away the pigment cells in the tail portion, 

 expand (fig. 12). They remain expanded for six hours and then 

 degeneration sets in. The melanophores in the anterior or head 

 end remain contracted. The contraction continues for eight to 

 twelve hours and then disintegration of the pigment cells occurs. 

 This justifies the conclusion that the reactions of the pigment 

 cells of trout embryos are in some way controlled by the higher 

 nerve centers. 



If the pigment cells that are contracted in picrotoxin are ex- 

 panded in 0.2 M. NaCl and are now placed in picrotoxin the 

 contraction is much slower than the first time. The sodium 

 chloride seems to counteract the action of the picrotoxin, 



3. Morphine. In embryos exposed to 0.5 per cent solution of 

 morphine hydrochloride the pigment cells remain expanded. 

 In a 0.12 per cent most of the pigment cells were expanded but 

 there were a few isolated areas that showed a contraction. After 

 an exposure of three hours these isolated areas of contracted 

 pigment cells had increased. In a 0.06 per cent solution of 

 morphine the result was the same. In a 0.012 per cent solution 

 no change occurred, all the pigment cells remained expanded. 

 There was no contraction of the pigment cells in a 0.005 per 

 cent solution. Pigment cells contracted by picrotoxin, potas- 

 sium iodide or strychnine were expanded by morphine.- Ac- 

 cording to Pouchet ('76), morphine did not cause any change 

 in the pigment cells of Gobius niger. Romanes ('77) has found 

 that in Aurelia aurita morphine had a highly depressing action. 

 Pickering ('93) found that morphine acetate depressed the 

 action of the heart muscle of embryo chicks. Cushny ('10) says 

 that the action of morphine on the central nervous system is a 

 mixture of stimulation and depression which are not equally 

 marked throughout the system; also, "there is a selective action 

 on the medulla oblongata in which certain centers are entirely 

 paralyzed before neighboring ones undergo any distinct modifi- 

 cation," Waller ('96) found that morphine applied directly to 

 the nerve had but little effect on its irritability. 



THE JOITRNAL OF EXPERIMENTAL ZOOLOGY, VOL. 23, NO 1 



