CHEMICAL AGENTS ON CHROMATOPHORES 153 



The above opinions tend to show that the part played by ions 

 in stimulation is by no means a settled question. In an attempt 

 to gain further insight into the subject brook trout embryos were 

 subjected to solutions of pure potassium and sodium salts. The 

 results have been so promising that the work is being extended to 

 numerous other salts. 



The salts used were of the purest of Merck's, Kahlbaum's and 

 Baker's manufacture. The solutions were made up in a 0.2 

 molecular concentration with oxygenated distilled water. The 

 solutions of the iodides which readily undergo decomposition 

 were never older than thirty-six hours when used. 



The experiments were carried on in Syracuse watch glasses in 

 about 10 cc. of the solution. At times small dishes of 25 to 50 

 cc. capacity were used. 



1. Effects of potassium salts. When the trout embryos are 

 immersed in a 0.2 M. KI solution a rapid contraction of the nor- 

 mally expanded chromatophores results within two or three 

 minutes. They then appear as minute dots with no peripheral 

 processes. In placing a similar lot into a 0.2 M K2SO4 equiva- 

 lent solution the change does not occur as rapidly, being com- 

 pleted in fifteen to twenty minutes. This at once suggested that 

 there is a specific difference in the rate of contraction for potas- 

 sium, varying with the anion. The experiments were extended 

 to include the following neutral salts of potassium, viz., K2SO4, 

 KCl, KBr, KNO3 and KI. Practically the first experiment 

 showed that there was a distinct difference in the rate of con- 

 traction varying with the anion. The rate and intensity of the 

 contraction was most rapid in the order given (figs. 1, 2, 3, 4 

 and 5). 



I> N03> Br> Cl> S04> 



In KI the contraction was complete before it had even begun in 

 KCl or K0SO4. The experiments were repeated many times and 

 as a check several of my colleagues were asked to come in and 

 arrange the sets showing the greatest change. In all cases their 

 arrangement was in the above order. This clearly indicates that 

 if contraction in the melanophore is specifically induced by the 



