Chemical constitution and toxicity

Abstract

IN many of the previous attempts to ascertain whether any definite relation- ship exists between chemical constitution and toxicity the principal difficulty has lain in the selection of a suitable biological standard.In the following investigation protozoa have been used for the measurement of toxicity.This choice was based upon two considerations: firstly, the uniformity (of bio- logical material) obtainable with protozoa cultivated in a synthetic medium was regarded as valuable; secondly, it was felt that the killing-power towards such a primitive organism afforded a measure of general protoplasmic toxicity and avoided specialised toxic effects.Some preliminary work by McCleland and Peters [1919] on the toxicity of certain arsenic compounds to Paramecium afforded an introduction to this investigation.Flury [1921] has, in a similar manner, utilised unicellular organisms as a means of comparing the toxicities of arsenic and other irritant compounds.Apart from these instanices, however, there appears to be a general recognition of the usefulness of protozoa in the measure- ment of pharmacological action. METHOD OF EXPERIMENTATION.Principle.The principle of the method adopted has lain in the determina- tion of the concentration of substance to be tested which killed all the organisms in a. given amount of culture in a fixed time.The unicellular organism used was Colpidium colpoda, a culture (derived from a single or- ganism) of which was in the first place supplied by Prof. R. A. Peters.This organism was cultured in the manner described by Peters [1921], in a simple synthetic medium, consisting of one organic and five inorganic salts; the ammonium glycerophosphate (0.06 %) of Peters's medium was replaced by sodium glycerophosphate (0.05 %) and ammonium chloride (0.01 %) owing to the greater degree of purity obtainable by recrystallisation of the sodium glycerophosphate.The culture was originally believed to be a pure one, but during the whole course of this work there has been present an apparently symbiotic bacterium.The possible influence of the presence of this foreign organism upon the toxicity results will be considered later.The cultures