276 Raymond H. Pond. 
RELATIVE TOXICITY WITH THE CONCENTRATIONS 
OF ENZYME DIFFERENT. 
One of the conclusions reached by Caldwell is that the metals 
maintain their ve/ative toxicity regardless of the concentration of the 
enzyme or of protein impurities. A relatively small increase of pro- 
tein impurity was found by him to very much increase the concen- 
tration of the toxic agent necessary for inhibition. The relative tox- 
icity of the metals remained the same, although the concentrations 
of inhibition were different. My own experience does not agree with 
this, as the following tests show. In the preceding tests I found 
Cobalt and cadmium to be equal, while zinc was four times more toxic 
under the conditions tried than either. From the following tables it 
will be seen that when the concentration of the enzyme is increased 
the three metals are about equal in toxicity. 
Zinc. — In this and in subsequent tests the controls were not boiled, 
because in the higher concentrations of the enzyme solution there is 
a flocculation on boiling, and in pipetting from such a boiled solution 
the coagulum cannot be as evenly distributed to the members of a given 
series as in the method used. This was simply to pipette the unboiled 
enzyme solution to each vial containing the toxic salt solution, and 
then to place the vials in cold water and bring the water to boiling. 
The controls, therefore, were not actually boiled, but the heat and 
the toxic salt combined were certainly adequate to destroy all activity 
of the enzyme. The tables show that this treatment insured a re- 
liable control. The concentration of the enzyme, as recorded in the 
table, was 0.125 per cent. It was, however, actually less. The paste 
formed by the trituration of 0.5 gm. in a few drops of water was 
diluted to 200 c.c. and filtered. Of that filtrate 2 c.c. were used 
in each vial, thus reducing the concentration of the enzyme by one 
half. Since so much residue remained upon the filter, the actual 
concentration of the enzyme must have been less than the percentage 
figures given. The coagulum on heating shows that the concentra- 
tion was at least greater than that used in the earlier tests, where 
Coagulation did not occur: 
TABLE XIII. 
ZINC. 
M. Reagent. Control. Enzyme. Increase. 
16384 0.00 0.15 1.10 0.95 
8192 0.00 0.15 1.05 0.90 
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