262 MEASUREMENT OF THE CATALYTIC POWER OF CATALASE 
a marked degree and are therefore to be avoided as much as possible. 
All authors, however, agree that, although the influence of accompanying 
salts may not be very great, damage by acid is considerable (G. Senter^). 
Therefore the physiologist must take care to neutralize the juice. A neu- 
tralization with Na2C03 worked in our experiments very satisfactorily. 
In experiments in which the same juice is used for several days, a few drops 
of toluol must be added as a preservative. 
The impurity of commercial peroxide should not be overlooked. It 
contains acid (even the perhydrol of Merck) which must first be neutralized. 
Also, most of these peroxides contain a certain amount of acetanilide 
(±1/15 percent). G. Senter has proved that aniline is poisonous to catalase. 
Therefore it is better to work with purified peroxide (methods by G. Bredig^). 
However, we shall try to show that, working with our method, the results 
are not greatly influenced by the impurities of the enzym or of the peroxide. 
We worked in these preliminary experiments with commercial lO-volume 
peroxide and freshly prepared, mostly undiluted, plant juice, neutralized 
during the grinding. We shall try the same method later on with purified 
chemicals and enzym. 
The third factor, that of the method of determining the quantity of 
oxygen liberated or of peroxide decomposed, is the most important one. 
There are three methods for the quantitative measurement of catalase. 
1. The method of Palladin (cited by A. Kasanski^) consists in measuring 
the height of the foam developed during the reaction. There is, however, 
no sufficient ratio between the intensity of the phenomenon and catalase 
activity. The purer the enzym, the smaller the volume of foam, etc. 
2. Titration with potassium permanganate. This is the method used 
by nearly all authors, but we have considerable doubt that it will serve its 
purpose. In the first place, organic compounds of different kinds oxidize 
permanganate. Therefore the press juice of itself, has a certain oxidizing 
power. This power is difficult to measure, not only because the end 
point of the reaction (a permanent red color) is difficult to observe, but 
also because the fluid is often so much colored that color reactions cannot 
be measured. These facts are stated by P. Waentig and A. Steche^ and by 
W. Issajew.^^ The latter does not mention his method, so that the value of 
his results could not be judged. Permanganate shows this uncertain end 
point also with all kinds of organic salts (citrates, malates, tartrates) as we 
were able to prove. Therefore it is not surprising that even excellent scien- 
tists like Bach sometimes made considerable errors with the titration 
method (A. M. Clover^^). Notwithstanding our working with the usual 
6 Zeitschr. Physik. Chem. 51. 1905. 
^ Zeitschr. Physik. Chem. 31. 1899. 
^ Biochem. Zeitschr. 39. 1912. 
9 Zeitschr. Physik. Chem. 72, 76, 79, 83. 1911-1915. 
10 Zeitschr. Physik. Chem. 42. 1905. 
11 Amer. Chem. Journ. 29. 1904. 
