28 
These solutions were prepared as follows: 0.032 gram of phenol- 
phthalin was dissolved in 21 c. c. of N/10 sodium hydroxide solution 
and diluted with redistilled water to nearly 100 c. c. 0.1 c. c. of 
M/1 hydrogen peroxide was then added and the solution made up 
to exactly 100 c. c. with redistilled water. Or, phenolphthalin was 
mixed in slight excess with 1 c. c. of N/10 sodium hydroxide solution 
and a small quantity of redistilled water, and after shaking thor- 
oughly was filtered and to the filtrate 20 c. c. of N/10 sodium h}Mrox- 
ide were then added, the solution made up to nearly 100 c. c. with 
redistilled water, 0.1 c. c. of M/1 hydrogen peroxide added, and the 
solution made up to exactly 100 c. c. with redistilled water. By this 
latter method weighings are obviated. It has been found further 
that for most blood work with this reagent it is sufficiently accurate 
to employ 0.1 c. c. of the 3 per cent commercial hydrogen peroxide 
solutions. It is scarcely necessary to state in this connection that 
only the purest forms of sodium hydroxide should be employed in a 
preparation of the N/10 sodium hydroxide used in making up the 
reagent, and also that redistilled water be used in the preparation 
of such solutions of sodium hydroxide. 
By closely following the above directions it has been found possible 
to prepare solutions of phenolphthalin in alkali containing the quan- 
tity of hydrogen peroxide required for the oxidation of the phenol- 
phthalin, which were without the slightest trace of pink color at the 
time of their preparation, and which, when preserved in glass-stop- 
pered bottles in a dark closet at ordinary temperature, showed only a 
faint trace of color, not measurable colorimetrically in the quantities 
of the solution employed in our observations, after forty-eight hours. 
In this way I have been able to overcome the difficulty encountered by 
Czyhlarz and Von Fiirth (43) in their attempt to measure the perox- 
idase activity of the blood by means of phenolphthalin. 
THE CONDUCT OF BLOOD TOWARD ALKALINE PHENOLPHTHALIN 
ALONE AND IN THE PRESENCE OF HYDROGEN PEROXIDE. 
It has been observed by Meyer (114) and Utz (191) and independ- 
ently by Kastle (80) that phenolphthalin in alkaline solution is 
oxidized by blood to phenolphthalein, and that the oxidation is 
greatly accelerated by hydrogen peroxide. Kastle and Amoss (80) 
found, further, that within certain limits the quantity of phenolph- 
thalm oxidized by a given amount of blood and hydrogen peroxide is 
nearly proportional to the concentration of the sodium hydroxide. 
As to the precise function of the alkali in such oxidations nothing 
definite can be said at present. It should be borne in mind, how- 
ever, that phenolphthalin contains two phenolic groups in its mole- 
cule, and that therefore, as is the case with other phenols, its oxida- 
tion is greatly facilitated by an excess of alkali. The fact that it is 
