2^1 BOTANICAL GAZETTE [april 



total inhibition four times greater equimolecular concentration of 

 silver is required than of mercury. (See also Pond, I. c. 268.) 



A critical examination of my own results and those of others fails 

 to reveal any general relation without exceptions, or any property 

 or factor that can be regarded as exclusively fundamental and as 

 solely determining the relative toxicity of a wide series of salts. 



Each of the salts I have tested is a nitrate except one, the chlorid 

 of mercury. The members of the series fall into two groups, the 

 neutral salts which do not hydrolytically dissociate in aqueous solu- 

 tion, and the hydrolytes which do so dissociate and whose soiution is 

 therefore acid or alkaline according to whether the H or OH ion is 

 predominant. All of the hydrolytes of my series are acid, but as the 

 dilution increases the acidity decreases to zero as here tested. 



This difference between the neutral salts and the hydrolytes shows 

 very clearly in the acidity of the controls. The controls of the neutral 

 salts have practically the same acidity as the enzyme solution itself, 

 that is, there is no evidence of any alteration of the acidity of the boiled 

 enzyme solution as a consequence of the mixture with the neutral salt 

 solution. Thus in Tables I-VII inclusive the acidity of the control 

 is about the same for each concentration of the salt. This acidity is 

 close to if not identical with the acidity of the plain boiled enzyme 

 solution as indicated by the figures corresponding to "Water." 



In the other tables, however, where the salts have an acid reaction 

 in consequence of their hydrolytic dissociation, the acidity of the con- 

 trol and of the reagent varies considerably (Pond, /. c. 283) . Thus 

 in Table VIII the acidity of the plain control without salt present is 

 o . 10. The acidity of m/1024 cadmium is o . 02, but when the control 

 for w/1024 is observed, the figure is o. 20 or considerably more than the 

 sum of reagent and enzyme. In regard to this behavior there is much 

 variation among the hydrolytes. Thus at the point of total inhibition 

 the reagent acidity and control acidity may be identical, as with copper 

 and zinc in Table IX, or considerably different, as in Table VIII 

 with cadmium. It is difficult to interpret this with assurance. 



It is notable that the neutral salts are not of equal toxicity either 

 in the saponification of the acetate or of the butyrate (Pond, /. c. 

 265, 266). Thus in Table VII barium is more toxic than hthium, 

 so that we cannot correlate the degree of toxicity with the degree of 



