REACTIONS OF FISHES TO ATMOSPHERIC GASES 249 



to be more active and probably more stimulated by the experi- 

 mental conditions. In the long experiments Ameiurus showed 

 a preference for the boiled water end but the high oxygen stock 

 showed the same in two out of three trials. 



b. Boiled water with oxygen added 



These experiments were essentially like the preceding ones but 

 oxj^gen was added to the boiled water end so that the amount 

 in solution was equal to that in the tap water. Thus the fish 

 encountered changes in water as described for the boiled water 

 gradient experiment with the exception of oxygen. The con- 

 trols were different from- the controls of other experiments, in 

 that boiled water was introduced into one end of the control 

 tanks and tap water into the other. The control was then an 

 experiment and the amount of reactions to factors other than 

 oxygen was determined by comparing the experiment and con- 

 trol. The general results are shown in table 15. Lepomis (ex- 

 periment 80) Hybopsis (experiment 78) Catostomus (experiment 

 82) and Notropis (experiment 77x) showed a time preference for 

 the boiled water with oxygen added, but the average time prefer- 

 ence was for the tap water, these being exceptions. The turn- 

 ings back in the gradient were not accompanied by any of the 

 characteristic reactions described for carbon dioxide. As a rule 

 the fishes turned back from the boiled water with oxygen added, 

 oftener than from the tap water, but Notropis, experiment 77 A, 

 furnishes an exception. 



In the controls (really experiments with boiled against tap 

 water) the fish gave practically the same reactions that have 

 already been discussed in treating of the reactions to the boiled 

 water gradient (p. 241). In general, the time preference was 

 much greater for the tap water while the number of turnings 

 was about the same for each end. The sharper reaction as 

 shown in the matter of time, shows the effect of oxygen upon 

 the reactions of fishes. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 14, NO. 2 



