156 JOHN N. LOWE 



duced by the sodium salts after a potassium salt contraction is 

 followed by a contraction of the melanophores in the usual 

 order. The position or order of the contraction was the same 

 as for the expansion of the melanophores; but with one excep- 

 tion where the NaNOs changed places with the NaBr. 



S04> Cl> N03> Br> I 



The extent to which the life of the fish and the irritability of the 

 melanophores are preserved is possibly the function of the 

 cation which is modified by the anion or the residual undisso- 

 ciated molecule. 



3. Discussion. All these results seem to lend themselves to 

 the interpretation that salt solution having a common cation 

 are modified by their anions or the residual undissociated mole- 

 cule. This is clearly shown by the rate and degree of the con- 

 traction of the melanophores by the potassium salts, where the 

 contraction may be specific for the cation of potassium. Speath 

 ('13) p. 547 says in speaking of the action of potassium salts: 

 ''The time of this contraction (K) is the same for the five salts 

 within the Hmits of the variation of the individual scales. Since 

 there is this common cation K+ in all five salts it seems prob- 

 able that the initial effect (contraction) is specific for the K+ 

 ions." My own results in the case of pigment cells of trout 

 embryos are contrary to this conclusion. If contraction is spe- 

 cific for the positive cation of potassium (K"*"), it should be the 

 same in rate and degree in all the salts of potassium. Since the 

 rate and degree of the contraction are not the same for the five 

 potassium salts (figs. 1, 2, 3, 4, and 5) it must depend on some 

 other or some modifying factor which is responsible for this 

 difference. 



A dissolved electrolyte conducts a current in proportion to the 

 extent that it is dissociated or ionized. Its maximum conduc- 

 tion will be at complete ionization which occurs at infinite dilu- 

 tion. Therefore the degree of the dissociation or the coefficient 

 of dissociations can be obtained from the conductivity of solu- 

 tion. The conductivity of an electrolyte divided by its num- 



