32 



From these data the question arises, whether the 

 influence of calcium nitrate in reducing the toxicity of 

 the copper salt may be due to a direct effect produced in 

 the solution or to some change brought about in the spore 

 itself. Kronig and Paul ( 1. c), in considering an effect 

 similar to this , in which the toxicity of HgCl2 upon 

 Bacillus anthracis was decreased by the addition of NaCl, 

 concluded that the change thus brought about is due to de- 

 pression of the ionization of the salt of the heavy metal. 

 That alteration in the ionization of Cu{NC2)2 cannot be the 

 cause of the diminution of its toxicity as here observed is 

 clearly shown by simple calculation from what is known as 



the isohydric principle. The percentage of dissociation 



used 

 of Cu(NC3)r. in the mixtures here /should be determined by 



the concentration of the NC3 radical. Following this gen- 

 eralization, the data given in Table I as" concentration of 

 dissociated CuCKCg )£ ,etc . ," have been obtained. Seventy 

 six per cent, of the copper salt of the first combination is 

 seen to be dissociated. Now if only one per cent, of the cop- 

 per salt here actually present in the mixture were ionized, 

 the concentration of the Cu ions would correspond to that in 

 a O.CCCOSra solution of Cu(N03)2 alone, which, as has been 

 shown, is stronger than is necessary to inhibit spore ger- 

 mination. It is therefore apparent that the decrease in the 

 toxicity of the copper salt shown in these combinations with 

 Ca(N02)2 are not to bo related to a decreased ionization of 

 Cu(NC3)2. 



