238 



VICTOR E. SHELFORD AND W. C. ALLEE 



shows the graph of the reaction of Notropis, which was the most 

 decided response given. It will be noted that Notropis turned 

 back from the low concentration several times during the first 

 fifteen minutes of the experiment but became very indefinite 

 during the last five minutes. A typical reaction of Lepomis is 

 shown in chart 2, experiment 75, of Hybopsis in chart 4, experi- 

 ment 73. The former was plainly indefinite in its reactions 

 throughout, but turned back more often from the higher concen- 

 tration. Ambloplites and Abramis did not turn back in the 

 gradient and gave no definite reaction. For the other fishes, 

 the number of turnings in the gradient indicates some reaction 

 to the absence of oxygen. 



TABLE 10 



Showing the reactions of fishes to a nitrogen gradient. The gradient was estabished 

 by running boiled water into both ends of the experimental tank and adding the high 

 nitrogen atmosphere at one end and enough oxygen to balance the oxygen added with 

 the nitrogen, at the other. Control in tap water. The difference in nitrogen secured 

 was only 3 cc. per liter. 



c. Reactions to nitrogen 



We were unable to secure pure nitrogen and did not succeed 

 in putting enough of this inert gas into solution under one atmos- 

 phere pressure to duplicate the high nitrogen content which is 

 sometimes found in the deeper waters of lakes. Two preliminary 



Chart 3 Showing the reactions of low oxygen Abramis to boiled water and of 

 Ameiurus to boiled water with acetic acid or ammonia added. Ammonia was 

 used in experiment 39; acetic acid in experiment 42. For detailed discussion, 

 see pp. 247, 252 and tables 13, 17 and 18. For a description of the method of 

 charting, see chart 1, p. 233. 



