110 ASYMMETRIC ANALYSIS 



toxic action are different in the racemate and in the laevo- 

 rotatory isomer. At temperatures from 16° to 26° C the 

 racemate is more toxic than the laevorotatory isomer, 

 whereas at the temperature of 31° C the latter is rela- 

 tively more toxic than the racemate. The temperature 

 characteristics of toxic action are also quite different. In 

 the laevorotatory isomer n = 12,300, and in the racemic 

 form |Li = 9,340. 



In similar experiments with the fry of Platypoecilus 

 maculatus results of the same kind as those obtained with 

 Lebistes were recorded (cf. Fig. 18). The temperature 

 characteristic of toxic action of the left isomer of malic 

 acid is 16,930 and that of the racemic form 12,880. 



The results obtained with fish were duplicated in a 

 study of the action of optically isomeric malic acids on 

 tadpoles of Rana temporaiia (Gause and Smaragdova, 

 1939). 



Some experiments on the action of l(-) and of d( + ) 

 leucine on the yeast Torula utilis (Gause and Smarag- 

 dova, 1938) also bring confirmatory evidence that the 

 unnatural form d(-|-) exerts a stronger action than the 

 natural and that their effect is of different nature. 



Concerning the experiments in which racemic malic 

 acid was used, it should be mentioned that, in dilute 

 aqueous solutions, the racemic acid is completely disso- 

 ciated into dextrorotatory and laevorotatory constituents 

 (Ostwald, 1889). Therefore the greater biological activ- 

 ity of the racemate must probably be attributed to a 

 higher toxicity of the unnatural dextrorotatory compo- 

 nent.^ 



If our last assumptions are correct there would be a 

 series of cases in which, contrary to what has been de- 

 scribed above, the unnatural optic isomers are physio- 

 logically more effective and in which the mechanism of 



lit is to be remembered that the natural dextrorotatory tartaric acid 

 and the natural laevorotatory malic acid belong to the same steric 

 series. 



