398 TRuE AND Gigs: Heavy METALs 
periment it appears that it is immaterial here, as before, whether 
the lighter metals enter the solution in compounds containing an 
anion common to that of the heavy metal, or whether the anions 
be different. 
DISCUSSION OF RESULTS 
From the evidence at hand in these experiments it appears that, 
in solutions of salts, the conspicuously effective component of the 
molecule is the cation or the metal. This presumption, raised by 
the similar physiological effects produced by the cation of various 
salts of the heavy metals in equimolecular quantities, is strength- 
ened by the action of mixtures containing a salt of the heavy metal 
with salts of lighter metals. 
In case several salts having the same cation are mixed in solu- 
tion the same lack of conspicuous influence on growth on the part 
of the anion is to be seen.* It is clear that the effect exerted upon 
the lupine roots by the salts of the heavy metals tested, differed ac- 
cording to the concentration of the salts. When sufficiently di- 
luted, solutions containing copper, silver, mercury or zinc ions ex- 
erted a more or less clearly marked stimulating effect on growth. 
Ata greater concentration, perhaps double that causing stimulation, 
a retarding influence was usually seen, and in a concentration ap- 
proximately doubling this, growth was much interfered with ; and 
on again doubling the concentration, little or no growth took place. 
The effect of adding solutions containing Ca, Mg or Na ions 
was seen to vary with the character of the cation introduced. In 
mixtures containing but two salts (Tables III and VI) sodium 
seemed to show an increased poisonous action as though that of the 
sodium were added to that of the cation of the heavy metal. When 
to a solution of copper, a salt of magnesium was added, the mix- 
ture seemed to act with nearly the same intensity as the simple solu- 
tion containing the copper in like quantity, exerting, therefore, 
little influence on the poisonous activity of the copper. When 
calcium was added, a marked reduction of the poisonous activity 
of copper ions was observed, a result seen even more strikingly in 
* The physiological action of every dissociated salt in solution is doubtless an expres 
sion of the resultant biological effect of its component cations and anions. In these 
experiments the influence of the cations was predominant. 
