Aug. 15, 1914 
Oxidases in Potatoes 
375 
resorcin, guaiacol, orthocresol, metacresol, paracresol, orthotoluidin, 
metatoluidin, and paratoluidin. 
In the case of each of the solid substances 0.05 gram was weighed out 
for each determination In the experiments with guaiacol 4 drops 
(0.15 gram) were used; by separate experiments it was shown that this 
quantity gave the highest result under the conditions of the experiments. 
The cresols and toluidins were found to be very poisonous, inhibiting the 
action of the potato oxidases when used in too great quantities. By a 
series of experiments it was found that 2 drops of each gave the 
optimum result. As in previous experiments, 1 c. c. of normal sodium 
hydrate was used in the glass basket in all experiments with pyrogallol, 
to absorb the carbon dioxid produced during the oxidation. 
All of the experiments described herein were carried out at 41 0 C. 
The apparatus used were all of the small type, in which a change in pres¬ 
sure of 1 cm. of mercury corresponds to the absorption of 1 c. c. of 
oxygen. The rate of shaking was 5 complete excursions in 3 seconds. 
All of the results were expressed in terms of the oxidase unit previously 
used by the writer. The unit is an oxidase solution of such strength that 
1 liter of it can bring about the oxidation of the equivalent of 1 gram of 
hydrogen (1912, p. 40). Blank determinations with the reagents here 
used showed that no measurable oxidase absorption took place under the 
conditions of the experiments in the absence of plant juice. 
The thermostat box was provided with a false bottom about 6 inches 
above the floor of the box and a free space of 4 inches at each end for 
the sake of free circulation. The heating lamps were all arranged below 
this false bottom. In this way very uniform heating throughout was 
attained. The stopcocks were closed through an opening just large 
enough to admit the arm, instead of opening a window, as was done 
formerly. To reduce still more the disturbances of temperature within 
the box, the opening for the arm was protected by means of a sleeve 
into which the arm was slipped. 
Although the results obtained with the method here used are more 
accurate and reliable than those obtained with any other existing method, 
yet this method is not entirely free from sources of error. It is probable 
that a part of the oxidases are destroyed by the shaking at the compara¬ 
tively high temperature (4i°C.). It is also probable that the reagents 
used for the oxidation act as poisons even in the small concentrations 
in which they are present. Probably, however, it will be only a matter 
of time before these possible sources of errors will be eliminated. For 
the present it may be said that the results were obtained in experiments 
carried out under identical conditions and are therefore comparable. 
In all the experiments the juice was pressed out of the ground pulp by 
hand and by the same operator. While it may seem that juices of more 
uniform composition might be obtained by pressing them out with a 
