CHEMICAL AGENTS ON CHROMATOPHORES 149 



contraction. Large doses produced an expansion of all the cells 

 which had contracted in the weak solution. Inasmuch as it has 

 been shown by various investigators that large doses of pharma- 

 cologically active agents produce a depression, and small doses 

 incite a stimulation in other tissues, it is inferred that the 

 condition is essentially the same with the melanophores. 



All the chemicals used in these experiments were of Merck's, 

 Kahlbaum's and Baker's manufacture. The solutions were 

 made up with oxygenated distilled water. Chemically pure 

 oxygen was bubbled through the water before it was used. This 

 precaution was taken because the distilled water was very low in 

 oxygen content and in it the pigment cells contracted. When 

 oxygen was added no such contraction occurred. The details 

 of the way in which the solutions were prepared are given under 

 the respective heads. 



The experiments with the salts and the alkaloids were carried 

 on in Syracuse watch glasses, which were kept covered to prevent 

 excessive evaporation. They were uncovered only when actual 

 observations were made. The amount of the solution used was 

 about 10 cc. Experiments were performed in stender dishes 

 of 50 cc. capacity as a check on the Syracuse watch glasses. 

 There was no difference in the results. The experiments with 

 volatile substances were carried on in wide-mouthed, glass 

 stoppered bottles, with a capacity of 50 cc. All precautions 

 were taken to prevent evaporation. 



Most of the experiments were carried on at room temperatures 

 which varied between 69° and 72° F., although some were per- 

 formed at the fish hatchery where the temperatures were from 

 46° to 50° F. 



The experiments with the alkaloids and alcohols were started 

 in solutions of 0.0001 per cent. The concentrations were in- 

 creased in multiples of ten. 



The experiments were repeated ten to fifteen times for each 

 solution tested. In many cases the experiments were repeated 

 double the number, in order to eliminate all possible individual 

 variation and errors. 



