PHYSIOLOGY OF CHROMATOPHORES OF FISHES 557 



This last experiment illustrates a peculiarity of certain mix- 

 tures of Na and K solutions which appeared repeatedly. Whereas 

 the melanophores are contracted in such solutions the xantho- 

 phores contract also. The former is a typical potassium reac- 

 tion and the latter a typical sodium reaction. This suggests 

 that these two salts may act selectively upon the two types of 

 chromatophores, the melanophores responding more readily to 

 the potassium stimulus and the xanthophores to the sodium. 



Experiments of the following type are of interest in their bear- 

 ing upon the question of a deferred antagonism between rela- 

 tively large quantities of potassium salts and small amounts of 

 sodium salts. 



June 12, 1912 



8.33 A.M. Scales from a 7.5 cm. female were immersed in a 0.1 M 

 NaCl solution. 



8.48 A.M. 3 scales were changed to A, 10 cc. 0.2 M KSCN + 1 cc. 

 M NaCl and B 10 cc. 0.2 M KSCN + 1 cc. water re- 

 spectively. The melanophores of both sets were con- 

 tracted in one minute and fifty seconds. 



9.14 A.M. All the melanophores were contracted in A but expanding 



inB. 

 10.25 A.M. Conditions in A unchanged; in B degeneration had begun. 

 10.55 A.M. Degeneration was very far advanced in KSCN B but in 

 A the melanophores were contracted. 



This and numerous other similar experiments with different 

 neutral salts of potassium have shown clearly that the addition 

 of NaCl to a solution of a potassium salt in such quantity as not 

 perceptibly to effect the initial contracting stimulus of the potas- 

 sium salt, may nevertheless protect the melanophores against 

 what has been clearly shown to be the deleterious (cytolytic) 

 action of its anion (a deferred antagonism) . This protective 

 action appears even though the sodium and potassium salt have 

 the same anion. The experiments with the neutral salts of 

 potassium have demonstrated quite clearly that the rapidity of 

 the degeneration varies with the anion. The conclusion there- 

 fore follows that in this case the melanophores are protected 

 against the cytolytic action of the anions of potassium salts by 

 the addition of small quantities of a sodium salt (chloride or 



