PHYSIOLOGY OF CHROMATOPHOREg OF FISHES 541 



tion, becomes unbalanced in that the NaCl exerts its individual 

 influence upon the melanophores. 



Sea-water preserves the irritability of the melanophores for 

 some hours. Thus the conbination of concentration (a hyper- 

 tonic solution) and the specific sodium chloride effect is only an 

 inhibiting and not a toxic one. 



The gradual loss of irritability s brought out in the following 

 experiment in which scales were transferred at regular intervals 

 from sea-water to a KCl solution to see how long the melano- 

 phores would continue to respond to this contracting stimulus. 



September- 4, 1912 



3.30 P.M. Scales from an 8 cm. female were placed in 10 cc. of sea- 

 water. This fish had previously been over a dark bottom 

 for about six hours. All the scales appeared very dark 

 with widely expanded melanophores. Individual scales 

 were now removed from the sea-water to a 0.1 M KCl 

 solution at half-hour intervals beginning at 4 p.m. The 

 first eight trials (until 7.30 p.m.) showed a complete con- 

 traction in KCl with an average contracting time of fif- 

 teen minutes. 

 9.30 P.M. A slight contraction lasting only three minutes." 



10 and 10.30 p.m. A very slight contraction was observed in a few 

 melanophores. 



11.00 P.M. No reaction followed immersion in the KCl solution. All 

 the melanophores remained widely expanded. T. = ca 

 23°C. 



At a somewhat lower temperature and differing with the indi- 

 vidual, the irritability of the melanophores may be preserved 

 even longer than six hours. In one case the melanophores re- 

 sponded to the contracting stimulus of KNO.3 more than eighteen 

 hours after removal from the fish. Further experiments showed 

 that the reactions of the melanophores in artificial sea-water 

 (van't Hoff's solution) were essentially like those in normal sea- 

 water. 



In distilled water, on the other hand, the irritability of the 

 melanophores rapidly disappears. Here again the time of the 

 reaction depends in part upon the temperature of the water. 



In order to detect the last traces of irritability after exposure 

 to distilled water scales were brought into a 1 per cent solution 



