394 . 



was run into either end (standing water). In the controls (Chart I) 

 the fishes usually swam from end to end in a rather symmetrical 

 fashion, and thus comparing these movements with those occurring 

 when the fishes encountered differences in water, we are able to de- 

 termine the reactions of the fishes to the differences. 



When the differences between the solutes at the two ends of the 

 tank were not great we found by chemical tests that the central portion 

 of the tank was a gradient between the characteristic waters intro- 

 duced at the two ends. Usually the end thirds were essentially like 

 the inflowing water. When the difference in concentration was great 

 the region of the gradient was proportionally longer and the ends with 

 the inflowing concentrations correspondingly shorter. When the dif- 

 ference in concentration was very great the entire tank was gradient. 

 For an experiment a fish was placed in a dish containing enough 

 water to barely cover it and set above the tank. When all was in 

 readiness the fish was liberated in the center of the tank. Marks on 

 the sides divided the tank into thirds. The fish nearly always swims 

 back and forth, apparently exploring the tank. The movements of 

 the fish were recorded graphically as shown in Chart I. 



For this purpose sheets of ruled paper were used. Four vertical 

 double rulings corresponded to the thirds and two ends of the tank. 

 Distance from right to left was taken to represent the length of the 

 tank, vertical distance to represent time and the graphs drawn to scale. 

 The width of the tank was ignored. The graphs on the following 

 pages are copies of the originals. The experiments were conducted 

 with water at about I7°C. 



Before or after the experiment, the headings of the sheets were 

 filled with data regarding the kind, size, and previous history of the 

 fish, the conditions in the tank, concentration of the solutes and other 

 significant data. The fish was observed continuously for twenty or 

 more minutes. Fishes are positive to waste in all concentrations tried. 



Fishes are positive or indefinite to illuminating gas, and to com- 

 binations of the most important illuminating gas constituents in both 

 acid water with 2-3 cc. of oxygen per liter and in alkaline water at 

 oxygen saturation (Chart II, graphs 11 and 12; Chart V, graphs 53 

 and 54). 



VI. The Toxicity of Illuminating Gas Waste Constituents. 



The following table shows the relative toxicity of the chief con- 

 stituents of gas-waste arranged according to the outline on p. 389. 

 On the pages following it are given occurrence of the substance, the 

 method of work, physiological effect, and the reactions of fishes. The 



