PHYSIOLOGY OF CHROMATOPHORES OF FISHES 549 



NH4CI. In such cases the malanophores were completely con- 

 tracted at the beginning of the experiment. These gave essen- 

 tially the same results as when the scales were first immersed in 

 sea-water. Whereas the scales in NaCl and NaBr showed ap- 

 proximately the same degree of darkness at first, the melanophores 

 invariably remained expanded longer in the chloride. Hence, as 

 regards the maintainance of the expansion, the sodium salts 

 clearly show the order 



Cl>Br>N03>SCN 



In NaSCN the melanophores never showed a very great ex- 

 pansion and the secondary contraction always occurred first in 

 solutions of this salt. Thus in striking contrast to the con- 

 ditions found in the corresponding series of potassium salts 

 in which the initial effect (a contraction) was identical through- 

 out the series, these salts of sodium vary in their initial effect, 

 the melanophores expanding most widely in NaCl and least in 

 NaSCN. Degeneration always occurs first in NaSCN. As in 

 the case of KSCN the epithelium becomes freed at the posterior 

 edge of the scale and eventually the xanthophores entirely dis- 

 appear. The melanophores lose their irritability completely 

 after about twelve hours in NaSCN whereas in NaCl, NaBr, and 

 NaNOs they may react to atropine sulphate more than five and 

 a half days (136 hrs.) after removal from the fish. After one 

 hundred and sixty hours in these salt solutions the melanophores 

 and xanthophores were still intact, but no longer irritable. In 

 these experiments no precautions were taken to prevent bacterial 

 infection. 



WTien these results are compared with those obtained with the 

 corresponding series of neutral potassium salts the following 

 differences appear : 



1. Potassium causes a contraction of the melanophores. The 

 time of this contraction is independent of the nature of the anion. 



2. Sodium causes an expansion of the melanophores. The 

 duration (and in part the degree) of this expansion varies with 

 the nature of the anion. 



