Solution Tension and Toxicity in Lipolysts. 273 
Even when the fact that silver is univalent is allowed for, it is very 
evident that in these tests mercury is much more toxic than silver. 
Of course the chlorid of mercury is compared with the nitrate of silver, 
but this was also the case when Mathews found silver more toxic than 
mercury toward Fundulus eggs. Here is also the interesting obser- 
vation that total inhibition may occur in neutral solutions at least 
neutral to the indicator under the conditions tried. 
Zinc with ethylbutyrate absent. — That no question may arise as to 
the validity of my controls in the foregoing experiments, the following 
test is given here. The figures show that in the concentration used 
boiling does not change the acidity of the enzyme solution or introduce 
a disturbing factor. The filtered enzyme solution (0.025 per cent) 
was divided into two portions. One of them was boiled a moment 
over the free flame. There was no flocculation and the merest trace 
of opalescence. The initial acidity of the boiled and of the unboiled 
portions was zero. Preparations were madc of the various concentra- 
tions of zinc nitrate, as indicated in the table, and after five hours’ 
incubation the acidity again determined. The concentration of the 
enzyme was reduced one half in making the preparations as usual. 
‘TABLE -XH: 
ZINC. 
» Reagent. Boiled. Unboiled. 
32768 s 0.00 0.00 0.00 
F638 0.00 0.00 0.00 
8192 0.09 0.00 0.00 
art 0.05 0.05 005 
2048 0.10 0.10 0.10 
1024 0.20 0.25 . 0.25 
512 0.45 e 0.45 0.45 
ati 0.90 0.80 0.80 
128 1.70. $40 iée 
64 3-49 3-40 3-40 
Enzyme, 0.0125 percent. Incubation period, 4 hours. 40° C- 
Ethylbutyrate absent. 
It is to be observed that the boiled and the unboiled solutions of the 
enzyme are identical in acidity in all the concentrations of the reagent. 
The control is therefore perfectly reliable, since, when the butyrate 
__ is added, any trace of acidity it carries is equally distributed. Also 
noticeable is the almost uniform agreement of the enzyme solutions 
