33O MORRIS M. WELLS. 



character of surrounding soil and incoming water, depth of 

 the water, season of year, daily temperature, animals present, 

 decaying organic matter, rainfall, exposure of the surface of the 

 water to winds. \Yith so many factors affecting the gas con- 

 centrations, they will vary greatly even within the same body of 

 water, at any given time. Birge and Juday (/. c.) have found 

 this to be especially true in small deep lakes, for different depths. 

 In my ow T n analyses of the waters of the Chicago region, I have 

 found horizontal differences that are also somewhat striking. 

 For instance the lower end of a fifty-foot pool in a small creek 

 may contain 5 c.c. per liter of oxygen less than the w^ater of the 

 upper end. Such variations are common and their influence 

 upon fish distribution must be marked. 



In describing the reactions of the different fish species, it will 

 be possible to give a general account which will stand in the 

 main for all the types of experiments. Given in chronological 

 order, the reactions were as follows: Upon introduction into the 

 treated water, the activity of the fishes was usually increased 

 for a short time. This increase was due in part to the handling, 

 but also in part to the stimulation of the water, since fishes 

 introduced in the same manner into normal water were not so 

 active. The greatest increase in activity came with introduction 

 into the low oxygen (0.1-0.15 c.c. per 1.) water. The period of 

 activity usually lasted for only 5 to 10 seconds at which time 

 some of the fish occasionally lost their equilibrium (e. g., small- 

 mouth bass), or they sank to the bottom or floated in the water 

 in an upright position. In all of the experiments, and especially 

 in the low oxygen, the opercular movements at once became 

 much more vigorous and continued so up till near the death 

 point. The time period between introduction and the appear- 

 ance of signs of loss of equilibrium varied with the combination 

 and concentration of the gases present. In general this period 

 varied directly as the lowness of the oxygen concentration or the 

 highness of the carbon dioxide. 



The fishes, upon sinking to the bottom, or upon becoming 

 quieter in the water above, rested for a longer or shorter period 

 and then began to "nose" more or less actively about the bottle. 

 Gulping occurred almost from the beginning. This is a normal 



