CHEMICAL AGENTS ON CHROMATOPHORES 165 



tion it has a stimulating action, ^nd (3) in very weak solution it 

 has no effect on the melanophores of trout embryos. Methyl 

 alcohol has a less pronounced stimulation action than ethyl 

 alcohol on pigment cells of trout It was necessary to double 

 to concentration so as to bring about reactions in any way com- 

 parable to those produced by ethyl alcohol. The action of 

 methyl alcohol was less striking and the stages of stimulation 

 and relaxation were slower in appearing than in ethyl alcohol. 



2. Ethyl alcohol. — When trout embryos were exposed to weak 

 solutions (0.01 per cent to 0.8 per cent) of ethyl alcohol, no change 

 took place in the pigment cells. Thie embryos did not show any 

 signs of depression and appeared perfectly normal. In solutions 

 of 1 per cent to 1.5 per cent the embryos became more restless 

 and the pigment cells exhibited a partial contraction. In con- 

 centrations of 1.6 per cent to 2.5 per cent of ethyl alcohol the 

 fish became more active, the pigment cells showed a complete 

 contraction; while in solutions of 3.0 per cent to 4.5 per cent 

 they showed a transitory contraction, followed by an expansion. 

 This result could be very easily overlooked. In 6 per cent to 

 10 per cent solutions the trout embryos died rapidly in from fif- 

 teen to twenty-five minutes, and there was no contraction of the 

 pigment cells. If embryos that had their pigment cells con- 

 tracted in the 2 per cent solution were transferred to a 7 per cent 

 the pigment cells expanded rapidly. 



If the embryos in which the pigment cells were contracted were 

 transferred to a 4.5 per cent to 6 per cent solution an imme- 

 diate expansion resulted. This expansion was due to the de- 

 pression caused by the high concentration of the alcohol, which 

 was far beyond the maximum threshold of stimulation. When 

 the fish which had their melanophores contracted in a 2 per cent 

 solution were placed in a 0.5 per cent solution they expanded. 

 Here the dilution of the alcohol was below the threshold stimu- 

 lus. If embryos that were exposed to 7^ per cent solution for 

 an interval of four to six minutes, were placed in water or very 

 weak alcohol, there was observed a contraction of the pigment 

 cells which was of a very short duration. This result was no 

 doubt due to the washing out or the dilution of the alcohol within 



