• 1
     A brief review is given of previous work on antagonism.
  • 2
     Lead nitrate and copper nitrate are highly toxic to Polycelis nigra (Müller). Lead nitrate is the more toxic salt at high concentrations, copper nitrate is the more toxic at low concentrations.
  • 3
     The addition of lead nitrate to a solution of copper nitrate reduces its toxicity to Polycelis. At any particular copper concentration the addition of increasing quantities of lead nitrate at first prolongs the survival time, which attains a maximum at 0–005 N Pb; with addition of further lead nitrate the survival time shortens, and at high lead concentrations the mixture solutions become more toxic than the pure copper solution. With decrease in the copper nitrate concentration the relative prolongation of the survival time at 0–005 N Pb increases.
  • 4
     Generally similar results are observed with Oammarus pulex (L.).
  • 5
     Lead nitrate also reduces the toxicity of copper nitrate to Tubifex tubifex Müller, and the tadpole of the frog, Rana temporaria temporaria L.
  • 6
     No case has been observed in which copper nitrate reduces the toxicity of a lead nitrate solution, and the antagonistic action of these salts thus appears to be of the non-reciprocal type.
  • 7
     The results are discussed in relation to the theories of other workers on the mechanism of antagonistic salt action.