CHEMICAL AGENTS ON CHROMATOPHORES 155 



in five to forty-five minutes. It was confirmed by repeated ob- 

 servation, that these contractions, slow as they may be for 

 certain solutions (Na2S04 and NaCl), were in the following 

 order : 



I> N03> Br> Cl> SO4 



A number of experiments were tried to determine if the sodium 

 salts produced an expansion of the melanophores after the po- 

 tassium salt contraction. The embryos were exposed to KCl 

 from fifteen to twenty minutes when they were removed and 

 rinsed in water to free them of the excess of KCl. They were 

 now placed into the five neutral salts of sodium. The rate and 

 degree of expansion was in the following order: 



S04> Cl> Br> N03> I 



The expansion was most rapid and complete in Na2S04 and NaCl. 

 In Nal there was no expansion. 



The experiments were repeated with embryos that were not 

 rinsed with water. The result was the same as in those that 

 were washed in water. If the melanophores are contracted with 

 KI instead of KCl the results are the same. 



S04> Cl> Br> N03> I 



It is interesting to note here that no expansion of the mel- 

 anophores occurred in the Nal solution. Is this because the 

 sodium cations are inhibited in permeating the cell membrane 

 due to the presence of the dissociated iodine anions or some other 

 factor? Are the cells permeable only to the iodine anions and 

 not to the cations of sodium? Hamburger and von Lier ('02) 

 claim that the blood corpuscles are permeable only for anions 

 and are not permeable to the cations. If the expansion of the 

 melanophore is specific for the sodium cation, it is overcome by 

 the antagonistic action of the iodine anion, which produces a 

 contraction. Nevertheless we must consider another factor, 

 that is, the action exerted by the residual undissociated molecule 

 which is present at all times in the solution. The expansion in- 



