A^O'MMirr/nc AXALYSf,^ 101 



but tlu' relation ot* tlie increase in toxicity with the con- 

 centration was the same in the two isomers and a com- 

 plete identity of the temperature characteristics of toxic 

 action of the dextro and laevo forms was also observed 

 (in cold-blooded animals: fishes and tadpoles). The 

 identity of the relation of toxicity to concentration and 

 the identity of temperature characteristics are taken as 

 an indication of the identity of the mechanism of toxic 

 action of the two isomers. Both of them seem to act on 

 the same link in the system of physiological processes, 

 though with diiferent speed. 



To illustrate these conclusions, let us consider in some 

 detail the results of recent experiments made with a brood 

 of the fish, Leuciscus idus var. orfiis (Gause and Smar- 

 agdova, 1939). The animals were placed in neutralized 

 solutions of nicotine of different concentrations, pre- 

 pared with redistilled water, and the killing time in sec- 

 onds was recorded. Figure 11 (upper part) represents 

 the relation of killing time to the concentration of nico- 

 tine. 



It is to be pointed out that in the calculation of the 

 relative toxicity of 1- and d- nicotine one cannot use indis- 

 criminately results taken at various arbitrarily chosen 

 concentrations. The relative efficacy of the isomers 

 changes with change in absolute concentration. For com- 

 parison of the physiological effect of the optical isomers 

 one has to employ such characteristics of corresponding 

 curves of toxicity which are determined not by any 

 values of the absolute concentration of the poison but 

 by some physiological action. The most convenient is to 

 take the minimal lethal concentration of the poison (the 

 constant n, cf. formula below). In 1-nicotine fh = 0.0022% ; 

 in d-nicotine >/,i = 0.0064%. The coefficient of relative toxic 

 action (a) = y?d/>^i, which indicates how nuicli the 1-isomer 

 is more powerful than the d-isomer, is 2.91. (This co- 

 efficient will be called, hereafter, the "stereo-coeffi- 

 cient.") 



