TOXICITY OF HEAVY METALS 69 



ferent concentrations of the calcium salt, ranging from 0.00003 12 5 m to 

 o.ooo625m, the spores germinated readily in those cultures where the con- 

 centration of Ca(NO 3 ) 2 was 0.0000625111 or higher. With the last named 

 concentration many local swellings were found, and also short swollen 

 tubes (see fig. 2), much as in the 0.00004111 concentration of Cu(NO 3 ) 2 

 alone. With the next lower concentration of the calcium salt, 0.00003 125m, 

 no germination occurred. 



From these facts it appears that the toxicity of o.oooim Cu(NO 3 ) 2 solu- 

 tion is so reduced as to be physiologically equivalent to a 0.00004111 solution 

 of the same salt, by the addition to the former solution of five molecules 

 of Ca(NO 3 ) 2 for every eight molecules of Cu(NO 3 ) 2 present. The addi- 

 tion of the lighter metal in this proportion pro- 

 duces the same effect as though the o.oooim cop- 

 per solution had been diluted to two and a half 

 times its original volume. 



Copper sulphate exhibits about the same tox- 

 icity toward these Gloeosporium spores as does 

 the nitrate. A series of combinations of this salt 

 with Ca(NO 3 ) 2 , quite similar to the series with Fig. 2. Germinating 

 Cu(NO 3 ) 2 just described, gave no germination spores from combination 

 in solutions containing 0.00003125111 concen- solution containing 



trations of the calcium salt, while germina- - 000 6m Ca(NO 3 ) 2 and 

 . . ' o.oooim Cu(N0 3 ) 2 , X6 5 o. 



tion occurred in some of the cultures con- 

 taining 0.0000625111 Ca(NO 3 ) 2 . In general, the effect of CuSO 4 , either 

 alone or in combination with Ca(NO 3 ) 2 , was practically the same as was 

 that of Cu(NO 3 ) 2 . This furnishes some additional evidence toward the 

 already rather firmly established conclusion, that the toxicity of copper 

 salts is due to the cations, and it also indicates the probability that con- 

 siderations bearing upon this toxicity need deal only with the cations. 



A series of experiments was carried out using o.ooo/mi Cu(NO 3 ) 2 in 

 combination with concentrations of Ca(NO 3 ) 2 ranging from 0.00025111 to 

 o.O25m. The spores in these combinations germinated readily in the pres- 

 ence of Ca(NO 3 ) 2 in concentrations ranging from o.ooim to 0.025111, but 

 no germination was found in combinations with 0.0005111 or 0.00025111 of 

 the calcium salt. The form and abundance of germination with o.ooim 

 Ca(NO 3 ) 2 was here much the same as that found in 0.00004111 of the copper 

 salt alone. Here a ratio of five molecules of the calcium salt to two of 

 the copper salt, the latter occurring in the solution at a concentration of 

 0.0004111, reduces the toxicity of the Cu(NO 3 ) 2 so as to produce an effect 

 on spore germination equivalent to that exercised by a 0.00004111 solution 

 of the copper salt alone. In other words, addition to a 0.0004111 Cu(NO 3 ) 2 

 solution, of Ca(NO 8 ) a in the molecular ratio of five of the latter to two of 



