Chart I. 



The graphs ou this chart show the movemeuts of fishes in the gradient tank 

 ^vhen no contaminating substance has been added at the end, and the water is there- 

 fore of equal purity throughout. Graphs 1-5 have been previously published. 



The gradient tank is shown in Figure 1, X, on preceding page. This is a diagram 

 of a longitudinal section of the lank. The left hand end was used for the introduction 

 of water such as the fishes were taken from and the right hand end was used for 

 the introduction of water to which the substance being tested had been added. The 

 water was introduced through a number of small openings in pipes which extended 

 crosswise at each end of the tank, midway between top and bottom. The water 

 flowed out at the center from both top and bottom. This gave pure water at the 

 left hand end and usually in the case of dissolved solids and liquids, throughout 

 about one third of the tank while the approximate full concentration of the polluting 

 substance extended throughout the right hand third. The central third contained 

 a mixture in which the concentration of the substance added at the right decreased 

 from right to left. The central portion of the tank was accordingly a gradient 

 between the two kinds of water introduced into the ends. The fishes introduced into 

 the tank usually swim from end to end. The record of the movements of the fish 

 was made by tracing their longitudinal movements in the tank on paper with reference 

 to a time scale. Thus in Graph 1 the fish passed from the center to the left end and 

 l)ack to the right end during the first minute. 



Graph 1 shows the longitudinal movements of a river chub made up as a com- 

 posite of a number of such graphs to show that on the whole no more time was 

 spent in one end of the tank than in the other. 



Graph 2 shows the movements of two individuals of the green sunfish. Where 

 the broken line appears, the t\^■o were moving separately. It will be noted that 

 fishes made long stays in the ends but usually moved back and forth nearly always 

 without turning back at the center. 



Graph 3 shows the movements of a golden shiner in a uniform tank. It will 

 be noted that the fish rarely turns around except at the end. 



Graph 4 shows the movements of a specimen of Notropis. There was little 

 activity and the fish turned back at the center once. 



Graph 5 shows the movements of a specimen of rock bass. 



Graph 6 shows the movements of a specimen of the orange-spotted sunfish. 

 This species often turned before reaching the end of the tank but the number of 

 turnings in the central third were the same from each direction. 



Graph 7 shows the movements of a long-eared sunfish. It sometimes turned 

 near the center, but about the same number of times from each end. 



