CHEMICAL AGENTS ON CHROMATOPHORES 161 



different potassium salts. In sodium salts the expansion of 

 contracted melanophores varied with the anion, and the con- 

 traction following this expansion was correlated with the anions. 

 In neutral salts of potassium there are two constant results 

 produced on the pigment cells of trout; (1) a contraction of the 

 pigment cells, (2) a cytolytic expansion. The times for each 

 varied with the anion. If the antagonism existed between the 

 potassium cations K +, and the negative anions SO4 — , Br — , 

 CI — , N03 — , I — , it was the least effective in KI and most potent 

 in K2SO4. The order of contraction and expansion was 



I> N03> Br> Cl> SO4 



In sodium salts there were two characteristic reactions, (1) an 

 expansion, (2) a contraction. The rate and degree of the ex- 

 pansion of the melanophores was greatest in Na2S04 and least 

 in Nal. The rate of contraction was rapid in Nal and least in 

 Na2S04. The order of the expansion was 



S04> Cl> Br> N03> I 



The contraction rate of the pigment cells was inverse to the 

 above. 



I> Br> N03> Cl> SO 



The cationic action was modified by the nature of the anion. 

 This anionic order was observed by Paul and Kronig ('96) on 

 the disinfecting power of mercuric salts of chloride bromide and 

 cyanide. Mathews ('06) has shown for the eggs of Fundulus 

 heteroclitus that the fatal dose varied with the anion. Loeb and 

 Cattell ('15) have shown that the hearts of Fundulus embryos, 

 previously poisoned by KCl, and recovered by sodium salts 

 was an anion effect inasmuch as it increased with the anion, 

 apparently in agreement with Hardy's rule (ion effect = ex- 

 ponential function of the valency) for the acetate was much 

 more efficient than the chloride. 



2. That it is the cation of potassium or of sodium that causes 

 the reaction of the pigment cells of trout embryos. 



Loeb ('10, '12) and Loeb and Wasteneys ('11a and 'lib) 

 maintain that there is an antagonism between the sodium cation 



