incomplete data were available. For the sake of uniformity, all formulated compounds were tested at the 

 routine concentrations used without regard for the proportion of active ingredient (s) present in each. 



The acetone or alcohol used frequently as a solvent exposed many test animals to concentra- 

 tions as high as 5 parts per 1000 of these substances. Repeated experiments were performed in which larvae, 

 trout, and biuegills were exposed to the maximum concentration of each solvent that could occur in any 

 screening test. No adverse effect on any species was observed at any time. 



Observations of each test were made approximately six times, at various intervals, during 

 the 24-hour test period. At each observation, the condition of every test specimen was determined and 

 recorded. Chronological histories were thus obtained of any symptoms of illness and the occurrence of 

 death. 



Any chemical killing the larval lampreys in eight hours or less at a concentration of 5. p. p. m. 

 (regardless of the effects on other fishes) was tested further at levels of 1.0 and 0.1 p. p.m. Water temper- 

 ature, test period, and procedures were identical with those described for the initial test at 5. p. p. m. 



FIGURE 1. Constant temperature troughs utilized in the screening program. 

 Concurrent tests of 48 different substances are shown in progress. 

 Routine observations are being noted on the individual test record 

 cards. 



