226 VICTOR E. SHELFORD AND W. C. ALLEE 



contained less than 1 cc, per liter but was increased by exposure 

 to the atmosphere in the box. Samples taken from the boiled 

 water end of the experimental tank contained more oxygen than 

 was normally present at this end, due to the unavoidable dis- . 

 turbance of the gradient while the sample was collected. The 

 experimental box was divided into three parts. Each end third 

 was filled with water flowing in at that end, while the middle 

 was a gradient between the two. 



The complete apparatus used in the experiment is shown in 

 figure 3. Two tanks as described above and shown in the figure 

 were placed side by side in the bottom of an aquarium (in the 

 absence of a suitable water table). The aquarium was enclosed 

 beneath a black hood with side curtains as shown in figure 3. 

 These side curtains hung loosely so that the observer could see 

 into the hood and into the experimental tanks from either side. 



Fishes were placed in each of two dishes which were set above 

 the experimental and control tanks respectively. Sheets of trial 

 balance paper were prepared by recording kind, size, number and 

 previous history of the fishes used, together with temperature, 

 gas content of the water, et cetera. Certain vertical rulings on the 

 trial balance paper were taken to represent the ends, center and 

 thirds of the tanks. Usually the right-hand side of the paper 

 was used for the main record. Vertical distance was used 

 roughly to represent time. 



Fig. 2 Shows the arrangement of the experimental tank in optical section, with 

 distances and dimensions. WS, tap water supply; C, hose end cock; Rt, rubber 

 tubing for tap water; Re, rubber tubing leading to the apparatus; Spc, screw pinch 

 cock over the tapped end of the hose; EE, level of the observer's eye, 45 cm. above 

 the surface of the water; L, the 4-candle-power lights, 30 cm. above the surface of 

 the water and above the center of the respective halves of the tank (the two lights 

 being the only source of illumination) and between the observer and the fish; Ta, 

 top of aquarium wall; T, is the tee introducer; Sc, the screen partition; D, drains 

 Rg, region of gradient; d, division points marked on the tank and corresponding 

 to the red rulings of the trial balance paper. The series of figures, 3.1 to 9.4 cc, 

 show the amount of oxygen present in collections taken from the gradient immedi- 

 ately above the location of the figures. 



Fig. 3 Sketch of the experimental tanks and hood in position, with the arrows 

 indicating the direction of the flow of water. The position of the lamps (L) and 

 of the observer (E) is indicated. The tank lettered (A) at the right hand is the 

 one usually used as the experiment in which case conditions are identical in the 

 ends marked {B). Other lettering as in figure 2. 



