1902] TOXIC PROPERTIES OF COPPER COMPOUNDS 33 
ascertained that fungi vary greatly in their resistance to deleteri- 
ous agents, according to variations in the medium in which they 
are cultivated when submitted to the influence of the agent. His 
results have not yet been published, but the importance of this 
matter in any toxicological studies necessitates considerable 
reference to the subject in this study of the toxicology of 
copper. 
The differences in resistance due to variations in the culture 
media may be due to two distinct causes: (1) All media 
influence the toxicology of electrolytes, and possibly other 
agents, by causing certain physical and chemical changes in the 
condition of the dissolved agent; (2) other things being equal, 
the more favorable the medium for germination and early 
mycelial development of a fungus, the more resistant that 
fungus will be to deleterious agents. 
The simplest case of changed physical or chemical condi- 
tions would be the diluting of the solution of the copper salt 
with pure water. Here, with each decrease in concentration, we 
get less and less of the whole molecule, e. g., CuSO,, and more 
and more of its component ions, tCu* and ~SOj, and the amount 
of change may be readily determined for any particular dilution. 
When the dilution is accomplished by adding an infusion or 
decoction of a vegetable or animal substance, however, a series 
of unknown reactions occurs, and even the amount of copper in 
the ionic form cannot be known. That these transformations 
have a very great influence on the toxic properties of the mix- 
ture is abundantly shown by the results represented graphically 
in fig. 2. A number of media tested caused precipitation of the 
copper, thereby rendering it harmless.? All such media were 
discarded and are not represented in the figure. 
When spores are placed in a medium which does not admit 
of growth (é. g., pure water) it is merely a question of time when 
these spores will be killed, if there be present a sufficient quan- 
tity of copper to precipitate the living proteids. It takes some 
°COPELAND and KAHLENBERG: The influence of the presence of pure metals 
upon plants. Trans, Wis. Acad. 12 : 454-474. 1900. 
