Effect of Organic Substances on Copper Sulphate 289 



cannot be neutralized up to the concentration recjuired for the com- 

 plete elimination of the organisms. It would appear, therefore, that 

 the apparent inhibition of the toxic efTect of the copper is due to the 

 formation of some non-toxic compound; that the formation of this 

 compound is due to a reversible reaction which is complete only at 

 the highest concentration of copper used; and that Ix-low this point 

 the addition of increasing amounts of copper sim{)ly brings aljout a 

 further reaction toward this non-toxic compound, producing a new 

 condition of equilibrium according to the law of mass action. 



Dextrose. — The effect of dextrose upon the coi)per sulphate seems 

 to be of a quite different nature. The following figures are calcu- 

 lated from the results of Experiment 4 : 



In the lower concentration dextrose neutralizes completely the 

 toxicity of the copper, so that the effect is about equal to that in the 

 control (Bottle 8). In the higher concentration the effect of the 

 dextrose is almost nil. This result, taken in connection with the fact 

 that the concentration of the dextrose is about -jV molar, and that 

 there are accordingly over 10,000 C^H.jOo molecules to each copper 

 ion in the one case and over 5,000 in the other, leads to the con- 

 clusion that the results obtained are not due to the formation of a 

 non-toxic compound. A careful study of the electric conductivity of 

 these solutions did not reveal any decrease in the normal conductivity 

 of the copper due to the presence of dextrose. It may be presumed, 

 however, that what has been called a "physiological compouml" 

 might be readily broken down under the inlluence of the electric 

 current. 



The following assumption seems to be in agreement with all the 

 facts: The bacteria doubtless attract to themselves by a process of 

 adsorption a certain amount of dextrose, and are thus surrounded 

 by a solution of this sugar more concentrated than that existing in 



