U. S. Bureau of Fisheries, 1 937 
Bulletin No. 22 
Figure 21. — Top, normal goldfish; bottom, goldfish killed in copper sulphate. Note thick deposit of opaque copper-mucoid 
precipitate covering body, fins, and eyes. This type of precipitate is produced by many wastes containing compounds of 
heavy metals. 
Figure 22. — Constant-temperature apparatus in which Daphnia magna were used as test reagents for toxicity of various 
stream pollutants. Assistant at the right is operating a concentrator preparatory to counting Daphnia. 
