PHYSIOLOGY OF CHROMATOPHORES OF FISHES 573 



is between cation and anion of the same salt (Na and K salts); 

 in the second, between different cations of two salts in which the 

 anion may be common. Other experiments with mixtures of 

 Na and K salts have shown that in a solution of a K salt in 

 which the Na salt is present in such quantities as not appreciably 

 to effect the initial K contraction, the presence of the Na may 

 nevertheless appear in its protective action against the cytolytic 

 effect of the K anion, there is thus a third type of antagonism 

 between the cation of one salt and the anion of another (p. 558). 



At the extremes of the alkaline cation series, the initial effects 

 of the chlorides of K and Na upon the two types of chromato- 

 phores are reciprocal. LiCl, which lies between K and Na, com- 

 bines the contracting effect upon the melanophores (a specific 

 K effect) with the contraction of the xanthophores (a specific 

 Na effect). It is thus physiologically intermediate between K 

 and Na, showing the effect of K on one type of chromatophore 

 and that of Na on the other. The time required for the contrac- 

 tion in a LiCl (p. 550) solution recalls the retarding effect seen 

 upon adding certain amounts of NaCl solutions of K salts. In 

 such solutions both types of chromatophores were contracted 

 also (p. 557). 



The reciprocal specific action of Na and K salts and their 

 mutual antagonism, has frequently appeared in experiments upon 

 other tissues (cf. Zoethout '02; '08). The recent work of Ishi- 

 kawa ('12) shows conclusively that the effects of Na and K salts 

 upon the chromatophores are not to be compared with the re- 

 actions of amoebae to these stimuli. In the later case isotonic 

 solutions produced identical and not reciprocal effects. 



Steinach ('92), Franz ('06), Hoffmann ('07) and others have 

 called attention to striking analogies between the responses of 

 the melanophores of fishes and certain types of smooth muscle 

 (sphincter pupillae and the radial muscles of the chromatophores 

 in cephalopods) . A series of experiments upon the reactions of 

 the sphincter pupillae and the stomach muscle of Fundulus to 

 salt solutions (K and Na) have shown that this analogy fails 

 when carried too far. 



