PHYSIOLOGY OF CHROMATOPHORES OF FISHES 543 



of the small proportion of sea-water appears in its protective 

 action against the characteristic distilled-water degeneration, 



4. The specific effect of NaCl accounts for the lasting expan- 

 sion of the melanophores and the contraction of the xanthophores 

 in dilute sea-water (p. 540). 



5. Although upon dilution the relative proportion of the salts- 

 remains the same as in normal sea-water (a 'balanced solution' of 

 Loeb), nevertheless the specific effect of the NaCl appears per- 

 fectly definitely in the responses of the chromatophores to such 

 dilute solutions. 



6. All movements of the melanin granules cease shortly after 

 immersion in sea-water but this is not due to its toxic action for 

 the melanophores may retain their irritability in sea-water more 

 than eighteen hours, at room temperature. 



7. In distilled water the melanophores lose their irritability in 

 about an hour, at room temperature. 



2. Effects of single electrolytes 



a. Potassium salts. A 0.2 M NaCl solution causes a lasting 

 expansion of the melanophores but an isotonic solution of KCl 

 produces a rapid contraction. It is therefore clear that these 

 characteristic reciprocal responses of the melanophores are not 

 dependent upon osmotic differences in the two solutions. 



If scales which have been in a 0.1 M NaCl solution until all 

 the melanophores show complete expansion, are immersed in a 

 molecular solution of KCl, a rapid contraction of all the melano- 

 phores follows immediately. This contraction is usually not 

 complete however in all the cells of a single scale. 



In less concentrated solutions, 0.5 to 0.01 M KCl the contrac- 

 tion is a complete one. Some time after the melanophores have 

 contracted the xanthophores invariably expand. This is quite 

 as characteristic a reaction as the contraction of the melano- 

 phores. At so great a dilution as 0.01 M the specific effect of 

 the salt is nearly obscured. Control scales in distilled water 

 show a contraction time which is only slightly greater than that 

 of the scales in 0.01 M KCl. Beyond this concentration the 

 specific KCl effect can no longer be detected with certainty. 



THE JOUKNAL OF EXPERIMENTAL ZOOLOGT, VOL. 15, NO. 4 



