TOXICITY OF ACIDS TO CILIATE INFUSORIA 



465 



when in molecular form are not more toxic than HCl of the same 

 Ph, it seems provable that their molecules do not exert a toxic 

 action. 



The curves for Euplotes present a slightly different picture. 

 Certain acids (oxalic, malonic, tartaric) become more toxic as 

 ionization is depressed. It will be noted that these are all 

 dibasic acids. They are, however, so nearly like HCl that it is 

 difficult to draw any definite conclusions from the results. With 



TABLE 4 

 Effect of depressing ionization 



the first addition of HCl the toxicity of many of the other acids 

 is decreased (lactic, formic, acetic, propionic, butyric, valeric, 

 citric, benzoic), proving that their anions must be toxic. Indeed 

 the decrease proceeds so far that the mixtures of these 

 acids with HCl become much less toxic than HCl of the same 

 Ph alone. Phthalic does something of the same sort, viz., first 

 becomes equal to HCl and then falls far below it in toxicity. 

 When the second lot of HCl is added to some of the acids (ben- 

 zoic, citric, acetic-valeric) a curious result is obtained. The 

 toxicity, instead of being decreased as by the first addition, is 



