PHYSIOLOGY OF CHROMATOPHOEES OF FISHES 547 



In these five neutral salts of potassium the initial effect is a 

 contraction. The time of this contraction is the same for the 

 five salts within the limits of the variations of individual scales. 

 Since there is this common time of contraction and the common 

 cation K+ in all five salts, it seems highly probable that the initial 

 effect (a contraction) is specific for the K+ ion. The time of the 

 secondary degeneration effect (expansion) varies with the nature 

 of the anion in the well-known lyotropic order 



Cl>Br>No3>I>KSCN. 



A little study of the plates (2 and 3) will show that what really 

 occurs is a gradual centripedal diffusion beneath the epidermis. 

 The melanophores play the part of indicators marking the advance 

 of the degenerating area. This is strikingly illustrated in such 

 scales as the KI after one hour and the KNO3 after two hours in 

 which there is a sharp line separating contracted and expanded 

 melanophores. Whereas in the case of the initial contraction 

 the centripedal diffusion is approximately equal on all sides, the 

 cytolytic effect always appears at the posterior torn edge of the 

 epidermis. As the degeneration proceeds, the epidermis becomes 

 freed from the underlying derma and when all the melanophores 

 are expanded (degenerated) the epidermis is completely detached. 

 It therefore seems quite certain that the diffusion occurs between 

 the epidermis and derma as was first suggested by the experiments 

 with sea- and distilled- water (p. 533). 



The experimental evidence thus indicates an independent 

 specific action of cation and anion, the cation effect always ap- 

 pearing first. These effects are furthermore exactly reciprocal. 



The question now arose whether the degeneration (cytolytic- 

 expansion) was due tothe specific nature of the anions or whether 

 it might not also be dependent upon the cation or some combined 

 interactivity of the two. In order to test this point, further 

 experiments were carried out with the corresponding series of 

 neutral salts of sodium. 



b. Sodium salts. A 0.1 M solution of NaCl brings about a 

 lasting expansion of the melanophores. A similar expansion oc- 

 curs in all concentrations of NaCl between 0.02 and 0.83 M. 



