EEACTIONS OF FISHES TO SALTS 267 



fish did become acclimated to the CaCl2 solution by the end of 

 a week and selected the higher concentration in the gradient. 

 Then after 2 days in the tap water it was negative to the salt 

 again. 



A like set of experiments was performed with a small bull- 

 head (6 in. long) with similar results; the acclimatization, how- 

 ever, came sooner. Neither of the fishes was fed while in the 

 CaCl2 and this would have an effect upon their reaction. The 

 fact that the rock bass became negative again after being returned 

 to the tap water indicates that the starvation did not account 

 for its positive reaction while being kept in the CaClo solution. 

 Starvation would tend to increase the negativeness of bull- 

 heads to the salt so the positive reaction upon being kept in the 

 CaCl2 can be due to nothing but acclimatization. The difference 

 in the effect of starvation upon the reactions of the two species 

 of fishes to salts is probably due to a difference in the metabolism 

 of the fishes and will be discussed in another paper. 



E. KESISTANCE OF FISHES TO SALTS 



The toxic effect of certain salts upon organisms has been the 

 subject for considerable investigation upon the part of other 

 workers (Ringer, Loeb, R. Lillie, and others) and therefore con- 

 siderable is known concerning the relative toxicity of the various 

 salt ions. In the present paper are presented data which indi- 

 cate that much of the work upon the toxicity of salts must be 

 reconsidered and correlated with the chemical reaction of the 

 water. The data show that the poisonous properties of a given 

 salt may vary within wide limits depending upon the amounts 

 of hydrogen or hydroxyl ions present in the solution. 



1. Resistance to ammonium salts 



According to Mathews ('07) the pharmacological action of 

 most salts is due to the ions of the salt. The kind of action 

 depends upon the character of the charge of the ion, i.e., whether 

 positive or negative; the degree of action is proportional to the 

 available energy in the ion. Ammonia salts are peculiar, how- 



