THE TOXICITY OF COPPER NITRATE SOLUTIONS TO POLYCELIS NIGRA II. Tim DUPLEX TOXIC MECIIANIS~ AND THE SYNERGIC EFFECt OF ADDED SOLUTES BY THEODORE WHITE

A very large number of investigations have been made of the relationship between the concentration of toxic substances in solution, and the extent of the toxicity produced at different concentrations. The problem has been studied from many viewpoints and the resultant mass of data has been well reviewed by Stiles (1924) and by Clark (1933). The latter, in particular, pays much attention to the variety of mathematical formulae which have been developed to express the toxicity/concentration relationship of toxic solutes--e.g, those of Ostwald (1907), Chick (1908), Reichel (1909), Powers (1917, 1920), Porodko (1926), Ponder (1932),--formulae developed as a result of work on plants and animals, living and dead. He comments particularly with regard to these expressions, that there has been virtually no attempt to explain their practical significance. I t ~eems to the writer that since the same fundamental phenomenon is involved in all this work, i.e. the reaction of a toxic substance with a protoplasmic substrate, it would be advisable, where possible, to arrive at some systematic basis whereby the mathematical expressions involved could be used to obtain an understanding of the basic processes at work in any case of toxicity. If this aspect is neglected, the derivation of mathematical formulae can serve no useful purpose. In the present contribution, it seems best to limit consideration of this aspect to the relationship Survival time/Concentration which has perhaps provided the most reliable previous data. Many cases of toxicity, involving study of this relationship, can be grouped according to the apparent (not necessarily the actual) number of variable factors controlling the dependence of the survival time t of an organism (or the toxicity as expressed by the reciprocal l/t) upon the concentration c of the toxic substance. In general, uni-univalent electrolytes, non-toxic organic compounds which kill only inhypertonic solution, and many drugs, give simple survival time/concentration curves expressed by t = KcP where K and p are constants and the plot log t/log c gives a straight line. Where such a simple relation holds, the toxicity may be termed "simplex," since the survival time appears to depend 31