270 | Raymond H. Pond. 
TABLE VI (continued). 
ZINC. 
2048 0.10 0.15 0.25 0.10 
102 0.20 0.30 0.33 0.03 
§12 0.45 0.45 0.45 0.00 
256 0.90 0.90 0.90 0.00 
Enzyme, 0.0125 per cent. Incubation period, 4 hours. 40° C. 
In this case 1024 of copper totally inhibits, while the corresponding 
concentration of zinc allows slight acidity. The difference is too 
small, however, to establish a positive difference in toxicity between 
the two salts. 
Copper and lead in contemporaneous test. — A long time test is 
given here to show that the relative toxicity of these two salts is not 
modified, although the point of total inhibition is different. 
TABLE VII. 
COPPER. 
M. Reagent. Control. Enzyme. Increase. 
4096 0.05 0.07 0.20 0.13 
2048 0.10 0.12 0.25 0.13 
1024 0.20 0.20 0.30 0.10 
512 0.40 0.40 0.45 0.05 
256 0.70 C.75 0.78 0.03 
128 1.40 1.50 1.50 0.00 
LEAD 
4096 0.00 0.10 0.25 0.15 
2048 0.05 0.20 0.35 0.15 
1024 0.10 0.30 0.40 0.10 
512 0.20 0.40 0.45 0.05 
256 0.45 0.60 0.65 0.05 
128 0.90 1.20 1.20 0.00 
Enzyme, 0.0125 percent. Incubation period, 17 hours. 40° C. 
The difference in acidity between the control and the plain reagent 
tends to be greater in the case of the lead than of the copper. This 
is also noticeable in other tables, so that it would seem as agape ebb 
action of lead on the enzyme is such as to generate acid products, 
More than in the case of copper. 
ercury, copper, and lead in contemporaneous test. —This test is to 
show that mercury exceeds copper and lead in toxicity. 
