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40

and Procedure. There were three replications of the same experiment, and the results of these were compiled and diagramed in figures 34 and 39. Maximum effects were recorded in each case after 220 hours of observation. Figures 34, 35, 36, 37, 38 and 39 give the results ten, 15, 30 and 60 second exposures, respectively.

Heptachlor exceeded all other chemicals, both with respect to rapidity and and magnitude of kill, in all but the 6o-second exposure where it was surpassed by aldrin. Furthermore, it showed a 77 per cent kill in the one second exposure and then diminished to 67 per cent with five seconds. The highest effectiveness of 9? per cent was achieved with 30 seconds exposure. It showed a decreased effectiveness again with 60 seconds where it gave only an 83 per cent kill.

Aldrin made a consistent increase in effectiveness from the start, except for a slight duration between the five and 15-eecond exposure periods. It started out with a 40 per cent kill at the one-second exposure and concluded with an 83 per cent kill at 30 and 60 seconds.

Dieldrin was similar in that it maintained a steady increase in effectiveness throughout the experiment, varying only slightly between the ten and 3O-second exposures. Its effectiveness at the onset was 19 per cent kill with one second exposure and culminated with a 72 per cent mortality in the 60-second exposure.

Even though the effectiveness of chlordane was improved with the longer exposures, it showed a rather inconsistent improved kill with increased exposures. There was no difference in its potency after the 30-second exposure, where it killed 55 per cent after 220 hours.