TOXICITY OF ACIDS TO CILIATE INFUSORIA 



451 



A further indication of specific differences is the fact that at 

 any one concentration the relative toxic order of the series is 

 different for each organism. Thus: 



Toxic order at 0.0002 N 



With all three organisms the most toxic acids are salicylic and 

 hydrochloric, while valeric and butyric are among the least 

 toxic. But here the similarity ends. The order for Stylonichia 

 disagrees with the order for Paramoecium in the position of 

 tartaric, formic, malonic, and oxalic. The order for Euplotes 

 is still more divergent, for citric and phthalic are more toxic, 

 lactic is less so, and tartaric and malonic instead of being nearly 

 as toxic as formic are here as little toxic as valeric. A few 

 observations were made on some other forms which gave the 

 following order of susceptibility : Paramoecium aurelia > Para- 

 moecium caudatum > Euplotes charon > vStylonichia pustu- 

 lata > Urostyla grandis > Euplotes patella > Vorticella. 

 Additional evidence of specific differences is presented in the 

 sections following. 



Although several experiments upon the cilia of other organ- 

 isms have been reported previously, it is almost impossible to 

 compare them, for they were made by different observers under 

 widely varying conditions. Thus in Barratt's experiments ('04, 



