Concentration-Survival Time Relationship for Roaches Injected with Arsenicals

Abstract

Injected into Periplaneta americana, Na monohydrogen orthoarsenate, like Na metarsenite, gave hyperbolic conc.-survival time curves having a region of inflection and a critical zone. Pb arsenate gave a curve that had a critical zone but no inflection. Na arsenate and Na metarsenite were equally toxic except in the higher cones., where the arsenite was the more toxic. The Pb arsenate was less toxic than either. On the basis of a dissociation hypothesis (discussed in a previous paper) the arsenical ions formed by Na arsenate and Na metarsenite (and probably by Pb arsenate) are equally toxic and their differences in toxicity are due largely to differences in their degree of dissociation. Survival times were calculated by equations based on this hypothesis. Curves of the "percentage dissociation" of poison in the blood of the insect were calculated. Methods for estimating the insect blood volume and for comparing toxicity symptoms caused by different poisons are suggested. Evidence is presented that the mealworm, Tenebrio molitor, is more resistant than P. americana to Na metarsenite.