TOXICITY OF ACIDS TO CILIATE INFUSORIA 



461 



These experiments with solutions of equal Ph also give evi- 

 dence of specific differences in resistance. The order of resist- 

 ance to every acid is Paramoecium > Stylonichia > Euplotes > 

 Vorticella. There is considerable evidence of specific difference 

 in resistance to H+ among other organisms, such as bacteria 

 (Michealis, '14, '15; Kemper, '16) it is noteworthy, however, 

 that here the limit of tolerance of a particular species is not the 

 same in all acids (Wyeth, '18). This is true also of Paramoe- 

 cium; thus, a concentration of Ph 3.5 kills Paramoecium in four 

 minutes in HCl, five minutes in tartaric, less than one minute 

 in valeric, etc., and so with the other organisms. The order of 



Graph 5, C Relative resistance of Paramoecium, Stylonichia, Euplotes, and 

 Vorticella to equal Ph of hydrochloric acid. Temperature 20°C.; time in 

 minutes. 



toxicity of the different acids at the same Ph also is slightly dif- 

 ferent for each organism (table 3) as is the case with equinormal 

 solutions. It will be remembered that Kopacweski ('14) found 

 the same condition in enzymes. 



E. Importance of anio7i and 'molecule 



Although there is ample proof from many sources that the 

 effect of an acid is not determined solely by its H ion concentra- 

 tion, there is very little evidence indicating exactly the part 

 played by anion and molecule. One way of approaching the 

 matter is to compare the relative toxicity of a series of acids 



