11 
the oxidizing power of blood. 5 c. c. of solutions (1) and (2) were taken 
and 2 e. e. of a normal blood solution. 1 cu. mm. to 250 c. c., added to 
each. The mixtures were then allowed to stand for the several inter- 
vals indicated below at the end of each of which the depth of color of 
each solution was determined by comparison with a standard solution 
of phenolphthalein in alkali by means of the colorimeter, the standard 
being set at 5 divisions on the colorimetric scale: 
READINGS OX COLORIMETER. 
Time. (1) (2) 
1 hour 17.1 1.9 
24 hours 17.25 5.6 
48 hours 18 4.1 
It is evident, therefore, that the amounts of phenolphthalin oxidized 
under these conditions are, for a short interval of time, nearly pro- 
portional to the concentration of the sodium hydroxide. 
It should also be borne in mind that in alkaline solution, blood alone 
has the power of effecting the oxidation of phenolphthalin. and that 
this oxidizing power is not completely destroyed by boiling, although 
it is considerably weakened. Were this direct oxidizing power of the 
bjood completely destroyed by heat, we should be inclined to refer 
its oxidizing power to the presence of an oxidase. If the oxidizing 
substance is really an oxidase, we must look upon it as possessing 
far greater stability than the plant and animal oxidases generally. 
Whether the oxidation of phenolphthalin by blood in alkaline solution 
in the presence or absence of hydrogen peroxide is referable to the 
same cause will be the subject of further investigation. It is sufficient 
for present purposes to bear in mind that at the dilution of blood 
employed in making these measurements of peroxidase activity — viz, 
1 cu. mm. of blood to 250 c. c. — the direct oxidizing power of the 
blood in alkaline solution is extremely feeble, whereas, in the pres- 
ence of hydrogen peroxide the oxidation of the phenolphthalin pro- 
ceeds with considerable velocity. 
MODE OF PROCEDURE. 
It was found, as the result of a few preliminary observations, that 
in determining the peroxidase activity of the blood by this method, 
the greatest care would have to be exercised in order to obtain reliable 
and comparable results. Such being the case, the following mode of 
procedure was agreed upon: In the tirst place, the work was so 
arranged that the collection of samples of blood, together with the 
determination of the amount of hemoglobin in the several samples, 
was left to Amoss, whereas the chemical measurements and also the 
