time than when hydrogen peroxide is present, and yet the other con- 
ditions of the experiments are essentially the same, except that slightly 
larger amounts of blood are employed in effecting the oxidation and 
slightly more phenolphthalein is formed as the result of the oxidation, 
and hydrogen peroxide is absent, or if present, only as a minute 
impurity in the reagents employed. Otherwise the general conditions 
of the experiments are the same in the two cases, and the same amount 
of sodium hydroxide is present at the same concentration. 
It is more than likelv. therefore, that the gradual fading out of the 
phenolphthalein color is not due entirely to any one of the three factors 
enumerated in the foregoing, but rather to a combination of causes, 
the complete effect of which it is impossible to picture at the present 
stage of this investigation. 
Suffice it to say in this connection, however, that this phenomenon 
in nowise invalidates either our results or the deductions therefrom. 
THE DIRECT OXIDATION OF PHENOLPHTHALIN BY BLOOD IN 
ALKALINE SOLUTION. 
Reference has already been made to the fact that in alkaline solution 
phenolphthalin is directly oxidized by blood without the intervention 
of hydrogen peroxide. It therefore occurred to us to make a few meas- 
urements of the direct oxidizing power of a number of specimens of 
blood from different individuals with the view of noting any possible 
variations that might exist among the several specimens in health and 
disease. 
Somewhat larger amounts of blood are required to effect the oxida- 
tion than when hydrogen peroxide is present. Accordingly in this 
series of experiments 1 cubic millimeter of blood was diluted to 100 c. c. 
with distilled water. Two cubic centimeters of this solution were then 
brought together with 5 c. c. of a reagent containing 0.032 gram of 
phenolphthalin and 21 c. c. A 10 sodium hydroxid at a total dilution 
of 100 c. c. 
These mixtures were allowed to stand in glass-stoppered bottles for 
the several intervals of time recorded in Table Xo. 2 , at the end of 
which the amount of phenolphthalein formed as the result of the oxida- 
tion was determined eolorimetrically by comparison in the colorimeter 
with standard solution of phenolphthalein Xo. 1. The results of these 
measurements are given in Table Xo. 2 . 
