576 R. A. SPAETH 



RbCl and CsCl, is uncertain. They lie very near KCl and 

 NH4CI, respectively. LiCl presents physiological properties in- 

 termediate between K and NaCl and combines the specific effects 

 of these two salts (p. 550). 



6. MgCl and MgS04 contract expanded melanophores but the 

 time of this contraction is clearly not a function of the number 

 of Mg++ ions in solution (p. 552). A comparison of these salts 

 shows that the nature of the anion has a distinct effect upon the 

 time of the first contraction. The dift'erence in the effects of 

 these two salts may be correlated with the greater association 

 of the MgS04. 



7. Mixtures of K and Na salts show two different types of 

 ionic antagonism: 



a. Between the cations, in which at 0.1 M concentrations K+ 

 appears to be about seven times as potent (specifically) as Na. + 

 (p. 558). 



b. Between the cation (Na+) of one salt and the anion of the 

 other salt (KSCN). 



8. Pressure causes a contraction of the melanophores and an 

 expansion of the xanthophores when applied to scales immersed 

 in a 0.1 NaCl solution. This reaction is reversible. 



9. Increase of temperature produces an acceleration of the 

 contracting effects of distilled water and KCl solutions. At 

 about 30°C. heat acts as a specific contracting stimulus which is 

 independent (1) of the amount of dissolved oxygen in solution 

 and (2) of the counter-acting stimulus of a 0.1 M NaCl solution. 



10. Oxygen is essential for the maintainance of the Na ex- 

 pansion. In its absence the melanophores contract even in a 

 0.1 M NaCl solution. The action of the oxygen in this case 

 seems to be a passive one since an expansion of contracted mel- 

 anophores was never induced even after a prolonged exposure 

 to an atmosphere of pure oxygen. 



11. Wliereas these experiments have thus far shown no evi- 

 dence of a response of the chromatophores to visible light of 

 varying intensity, an exposure to ultra-violet light (185-290 /xfj.) 

 of inverted scales immersed in a 0.1 M NaCl solution produces 



