558 • R. A. SPAETH 



bromide) and since the anions of the two salts may be identical 

 it seems highly probable that the Na+ cation antagonizes the 

 anion of the potassium salt. 



These experiments with mixtures of potassium and sodium 

 salts have thus shown that: 



1. The specific effect of potassium is approximately 7 times 

 as great as that of sodium (KCl vs. NaCl at 0.1 M concentration.) 



2. The nearest approach to a balanced solution is one that will 

 both expand contracted and contract expanded, melanophores, 

 depending upon their previous treatment. This expansion and 

 contraction is never so great as in the corresponding pure 

 solutions of NaCl and KCl. 



3. The melanophores retain their irritability longer in such 

 mixtures than in pure solutions of either constituent. 



4. The chromatophores may react to two salts of a mixture 

 simultaneously — the melanophores being contracted by the po- 

 tassium and the xanthophores by the sodium salt. 



5. The addition of an amount of sodium salt which does not 

 appreciably affect the initial contraction of a potassium salt so- 

 lution may effectively protect the melanophores against the sec- 

 ondary degeneration which is normally brought about by the 

 cytolytic action of the potassium anion. This result suggests 

 an antagonism between cation and anion of different salts. 



3. PRESSURE EFFECTS 



Upon purely theoretical grounds v. Frisch ('11 a) claimed that, 

 since the stimulated phase of the vertebrate melanophores is 

 certainly the contracted one, it would be very surprising to find 

 that the pressure stimulus caused an expansion as several of the 

 older investigators have thought to be the case. He drew a dis- 

 secting needle lightly across the surface of both living and dead 

 minnows (Phoxinus laevis, L.). The effect was exactly com- 

 parable to marking with a pencil upon a sheet of white paper. 

 Examination under the microscope showed the melanophores to 

 have been destroyed along the path of the needle and the black 

 effect to be due to melanin granules which had diffused from the 



