74 M. E. COLLETT 



2. The fact that the toxicity of the mixture is unchanged by a 

 small addition of HCl, although the pH is slightly increased, may 

 be due either to the disappearance of the toxic organic anion or 

 to the partial antagonism of the molecule by HCl. 



3. Of the acids studied, only saUcylic, benzoic, and citric 

 have anions which are toxic in concentrations of 0.01 M or less, 

 as judged by the behavior of their sodium salts. 



4. The relative toxicity of the sodium salts 0.01 M is: 

 Paramecium: salicylate > benzoate > tartrate = succinate > 



citrate > formate = valerianate = chloride = lactate. 



Euplotes: citrate > salicylate > benzoate = tartrate > 

 succinate > formate = valerianate = lactate. 



5. Mixtures of certain acids (formic, acetic, butyric, valeric) 

 with non-toxic concentrations of their salts are more toxic than 

 can be accounted for by the pH of the mixtures. Benzoic and 

 salicylic (with both organisms) and citric (with Euplotes) when 

 mixed with a dilute solution of their Na-salts are also more toxic 

 than can be accounted for by the pH or by the toxicity of the 

 salts. This evidence seems to indicate that the molecules of such 

 acids are in themselves toxic. 



6. There is no evidence of toxicity on the part of anion or mole- 

 cule of lactic, succinic or tartaric acids at the concentrations used. 



It is a pleasure to record my indebtedness to Dr. R. S. Lillie, 

 in whose laboratory at Clark University this work was done, 

 for his help and interest in the problem. 



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