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1. A brief review is given of the various types of living material and of toxic substances employed by different workers in the study of antagonism. 2. Survival curves are described for the heavy metal salts nickel nitrate, copper nitrate and cadmium nitrate, and the alkaline-earth metal salts magnesium, calcium, strontium and barium nitrate, for the tadpole of the toad, Bufo bufo bufo (L.). 3. A description is given of Osterhout's method for the detection and measurement of antagonism by observing the effect of mixing, in varying proportions, equally toxic solutions of the two substances in question. 4. Survival curves for tadpoles in mixtures of equally toxic solutions of nickel nitrate and strontium nitrate indicate marked antagonistic action between these salts, the effect increasing with dilution. 5. The survival curve for mixtures of the equally toxic solutions 0.03 N copper nitrate and 0.04N strontium nitrate apparently indicate antagonism over a part of the concentration range and synergism over the remainder. This is because a 0.03 N solution of copper nitrate increases in toxicity upon dilution, its toxicity reaching a maximum at approximately 0.0015 N. If the normality of the copper solution is below this critical value its mixture with an equally toxic strontium solution gives a normal antagonism curve. 6. It is shown that the other alkaline-earth metals, calcium, magnesium and barium also reduce the toxicity of copper solutions. The strontium concentration--copper concentration--survival time relationship is studied in detail and the way in which the survival time locus is represented by a curved surface is described. The survival surfaces for copper and calcium, copper and magnesium and copper and barium are of similar type. 7. Problems for further investigation arising out of the results are briefly discussed.

Antagonism between Salts of the Heavy and Alkaline-Earth Metals in their Toxic Action on the Tadpole of the Toad, Bufo Bufo Bufo (L.)