70 LON A. HAWKINS 



the copper Salt, has the same effect as diluting the Cu(NO 3 ) 2 solution to 

 ten times its original volume. 



A third series of combinations of the same two salts, but with higher 

 concentrations, was carried out in a manner somewhat different from that 

 employed in the preceding series. Here the concentration of Ca(NO s ) 8 

 was the same (o.o5m) in all of the cultures, while that of the copper salt 

 varied. The concentrations of Cu(NO 3 ) 2 ranged from 0.00025111 to o.oim, 

 and the spores germinated in all the concentrations used except the highest. 

 With a concentration of o.ooSm Cu(NO 3 ) 2 germination was similar to 

 that found with 0.00004111 of the copper salt without the addition of 

 Ca(NO 3 ) 2 . From this series it appears that addition to the Cu(NO 3 ) 2 solu- 

 tion here used (o.ooSm), of about six molecules of Ca(NO 3 ) 2 for each mole- 

 cule of the copper salt present in the solution, reduces the toxicity of the 

 latter compound in the same way as though the solution had been diluted 

 to two hundred times its original volume. It appears as though the presence 

 of Ca(NO 3 ) 2 , in this molecular proportion of about 6 to i, altered the 

 relations between spores and solution so that only a two-hundredth part 

 of the copper nitrate actually present was effective to modify or retard 

 the germination processes. 



A series of combinations of Cu(NO 3 ) 2 with KNO 3 was carried out, 

 in which 'a constant concentration of the potassium salt, 0.05111, was used 

 in combination with Cu(NO 3 ) 2 in concentrations ranging from 0.0002111 to 

 o.oim. The spores germinated in concentrations up to and including 0.002111 

 of the copper salt. In the last mentioned concentration, the form of 

 germination was quite similar to that found in a 0.00004111 solution of the 

 copper salt alone. Thus in a solution containing KXO 3 at a 0.05111 con- 

 centration and Cu(NO 3 ), at a 0.002111 concentration (a molecular ratio 

 of 25 of the potassium salt to i of the other), the toxicity of the copper 

 salt is decreased to a magnitude only one fiftieth as great as is that shown 

 by this concentration of the copper salt alone. 



The results of the three series of combinations of copper nitrate with 

 calcium nitrate which have been described, are summarized in table I, 

 together with certain other data which require consideration. 



From the data just given 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 [97], in considering an effect 

 similar to this, in which the toxicity of HgCl 2 upon Bacillus anthracis 

 was decreased by the addition of NaCl, concluded that the change thus 

 brought about is due to depression of the ionization of the salt of the 

 heavy metal. Such a supposition cannot apply in the present case, how- 

 ever; that alteration in the ionization of Cu(NO 3 ) 2 cannot be the cause 



