466 M. E. COLLETT 



sharply increased, until the mixture again becomes equal to 

 pure HCl. This is indicated though much less clearly in the 

 Paramoecium curves for citric and acetic, propionic, etc., but 

 not for benzoic. Until further work is done I cannot with assur- 

 ance offer a definite explanation of this condition, but the results 

 so far suggest that the molecule is to some extent capable of 

 antagonizing the action of the H ion. Thus as dissociation is 

 depressed and the anion is removed from the sphere of action, 

 antagonism between molecule and H ion may cause the mixture 

 to become less toxic than HCl of the same Ph, and this antag- 

 onism may cease to be important only when the H ions largely 

 out-number the molecules present. 



From this series of experiments we find that the following 

 anions are toxic. To Paramoecium: formic, acetic, propionic, 

 butyric, valeric, benzoic, phthalic, lactic, oxalic, malonic, tar- 

 taric, citric. To Euplotes, all of these except oxalic, tartaric, 

 lactic, and possibly malonic. These findings agree with the 

 conclusions suggested by the previous experiments, viz., that the 

 anions as well as the H ions are sometimes toxic, and that the 

 same acid need not act upon different organisms in exactly the 

 same way. 



F. Nature of the toxic action 



At higher concentrations (0.0005 N) Paramoecium discharges 

 trichocysts, and as it coagulates turns rapidly opaque without 

 great swelling, but at 0.0002 N the swelling is pronounced and 

 no trichocysts are discharged. At death the protoplasm be- 

 comes granular and the nucleus stands out sharply. Vorticella 

 and Euplotes, too, become granular and in all the vacuoles 

 grow large and rigid before death. The cilia themselves swell 

 and become sticky, the beat grows irregular and slows until 

 finally the cilia dissolve (see also Koltzoff on Carchesium). 

 Stylonichia swells and some of its vacuoles increase in size, then 

 anteriorly, at a point near the edge, the protoplasm dissolves 

 and releases large apparently insoluble droplets. The cilia stop 

 only when the body is completely disintegrated and must there- 

 fore be more resistant than the rest of the cell. Careful obser- 



