A micro burette, micro pipette, and methods for their use in quantitative toxicological investigations on mandibulate insects are described.

It is suggested that the form of curves relating speed of toxic action to dosage may be explained by postulating suitable changes in rate of distribution, excretion, and cell penetration of poison as dosage varies.

The speed of toxic action of pentavalent arsenic in the silkworm is proportional to an integral power of the dosage at lower concentrations, and to a fractional power of the dosage at higher concentrations.

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