252 MORRIS M. WELLS 



d. Calcium nitrate. At Chicago 20 (40-min.) experiments were 

 run with this salt. The reactions of the fishes were so decidedly 

 negative that further work seemed unnecessary. At the Uni- 

 versity of Illinois, it was decided to repeat the experiments with 

 calcium nitrate as a check upon the reactions of the fishes in the 

 two waters. To this end a series of experiments with O.OIN 

 Ca(N03)2 in neutral water, was run. The results were very 

 different from those obtained at Chicago. There the fishes had 

 shown a 90 per cent negative reaction to this salt in O.OIN con- 

 centration, while at Illinois in the neutral water, the reaction 

 was 50 per cent negative and 50 per cent positive. In other 

 words they seemed to be indifferent to the salt. It was thought 

 that the explanation of the Illinois reaction might lie in the fact 

 that, since calcium nitrate hydrolizes to give a faintly acid solu- 

 tion, the fishes, which (Wells '15 a) had already been shown to 

 be negative to the neutral water, were reacting to this acidity. 

 This proved to be the case, for when the experiments were re- 

 peated in moderately acid water, the fishes gave an 80 per cent 

 negative reaction. 



To make doubly sure of the results with the calcium nitrate, 

 a final series of experiments was run in distilled water, which 

 it will be remembered is slightly acid with COo (2-3 cc. per 

 liter). Five 15-minute graphing experiments were run with 

 results that show a 75 per cent negative reaction. An experi- 

 ment with 4 bull-heads (3-5 in. long) was read 50 times at 30- 

 second intervals. Computation showed that the fishes had spent 

 74 per cent of the time in the negative half of the tank. Thus 

 the reactions at Chicago and at Illinois, when slightly acid water 

 is used, are in close agreement in showing the negative reaction 

 of fishes to O.OIN concentration of calcium nitrate. 



e. Magnesium nitrate. Twelve experiments were performed 

 with this salt at Chicago; they showed a 100 per cent preference 

 for the tap water half of the tank. The negativeness was more 

 marked in some experiments than in others but in none did the 

 fishes swim into the salt end. The experiments have not been 

 repeated at Illinois. 



