TOXICITY OF HEAVY METALS 81 



Zinc. 



Zinc nitrate, alone and in combination with the nitrates of calcium and 

 magnesium, was studied in much the same way as were the nitrates of 

 copper and lead. Zinc nitrate alone inhibited germination in o.25m concen- 

 tration. Many local swellings of the spore walls were found in concen- 

 trations of o.oSm and 0.04111, while local swellings and short tubes were 

 present in concentrations of 0.008111 and 0.004111. Normal germination 

 occurred with the concentration of o.oo2m. Combinations of Zn(NO 3 ) 2 

 with Ca(NO 3 ) 2 and Mg(NO 3 ) 2 were tested, using a concentration of 

 0.04111 Zn(NO 3 ) 2 . In these combinations the calcium salt was employed 

 in concentrations ranging from 0.000125111 to o.O2m. Some normal germ- 

 ination occurred with all concentrations of Ca(NO 3 ) 2 below and including 

 that of 0.0005111, but none was observed in the mixture containing a 

 o.oooi25m concentration of this salt. It thus appears that, normal germ- 

 ination of these spores may be brought about in a 0.04111 Zn(NO 3 ) 2 solu- 

 tion, by the addition of Ca(NO 3 ) 2 in the proportion of one molecule of this 

 to every 80 molecules of Zn(NO 3 ) 2 present. 



The concentrations of Mg(NO 3 ) 2 which were employed in these com- 

 binations with the 0.04111 solution of Zn(NO 3 ) 2 ranged from 0.00025111 to 

 0.025111. Here it was found that no normal germination occurred until the 

 magnesium salt reached a concentration in the mixture of 0.0025111. This 

 means that to produce any normal germination in the Zn(NO 3 ), solution 

 here used, by addition thereto of Mg(NO 3 ),, it is necessary to add one 

 molecule of the latter salt for every 16 molecules of Zn(NO 3 ) 2 already 

 present. It therefore requires five times as much of the magnesium salt 

 to counteract the toxic influence of Zn(NO 3 ) 2 in the concentration here 

 used (0.04111) as is required of the calcium salt to produce the same effect. 



The relatively small amounts of the calcium and magnesium salts, which 

 are required to inhibit the toxic effects of Zn(NO 3 ) 2 in 0.04111 concentra- 

 tion, preclude any possibility that the antagonistic influence of either of the 

 former salts might be related to decreased dissociation of the zinc salt, 

 brought about by their addition, so that this consideration needs no atten- 

 tion in this case. 



It is interesting to recall here that the effectiveness of Mg(NO 3 ) 2 in 

 counteracting the toxicity of Pb(NO 3 ) 2 , in the two concentrations studied, 

 so as to allow some normal germination of the spores, was also found to 

 be only about one fifth as great as that of Ca(NO 3 ) 2 . The relative effec- 

 tiveness of the nitrates of calcium and magnesium thus seems to be the 

 same whether they are employed to counteract the toxicity of Pb(NO 3 ) 2 

 or that of Zn(NO 3 ) 2 . 



Zinc nitrate did not seem to stimulate the spores to form appressoria, 

 though hyaline swellings were common in the more concentrated solutions. 



