49 
of phenolplithalin, but fails to oxidize it when hydrogen peroxide is 
present. Lead and mercuric chlorides oxidize it slowly when hydro- 
gen peroxide is present, hut fail to oxidize an alkaline solution of 
phenolphthalin alone. Potassium ferricyanide rather rapidly oxi- 
dizes an alkaline solution of phenolphthalin in the absence of hydrogen 
peroxide, but oxidizes it more slowly when hydrogen peroxide is 
present. In other words, despite the fact that a few of the salts of 
the heaA^ metals exhibit certain resemblances to blood in their 
conduct toward one or the other phenolphthalin reagents, it would 
seem that when tested with both reagents they all display certain 
well-marked differences from blood, whereby we coidd readily tell 
the difference between blood and any one of these substances. It 
might be possible to prepare a solution or a stain which could not be 
told from a solution of blood or a blood stain b}^ means of the phenol- 
phthalin reagents, but up to this time such a solution or stain lias 
not been encountered. 
To attempt, therefore, to convey the impression that phenol- 
phthalin is without utility as a reagent for blood and the oxidases, 
as has been done by Pozzi-Escot, appears to me to be entirely unwar- 
ranted and unjustifiable in the light of the facts. As a matter of 
fact, all really delicate tests have to be controlled and used Vvuth 
considerable circumspection and discrimination in order to arrive 
at the proper conclusion from the findings, and it not infrequently 
happens that the less one knows of analytical methods the more 
certain he is of the results of the analysis. 
THE EXAMINATION OF A NUMBER OF UNKNOWN STAINS BY 
MEANS OF THE PHENOLPHTHALIN REAGENTS. 
In order to form a better idea of the practical utility of the alkaline 
phenolphthalin reagents (2) and (4), in the actual examination of 
blood spots, 25 spots or stains upon filter paper, not exceeding 4 
square millimeters in area, were prepared by Mr. Elvove, one of the 
workers in the Chemical Division of the Hygienic Laboratory, and 
submitted to the writer for examination. At the time of the examina- 
tion the nature and composition of the stains were known only to 
Mr. Elvove. Within two hours after these unknown stains had been 
submitted to the writer three of them, viz. Nos. 3, 12 and 17, had 
been found to contain blood, and Nos. 1, 2, 5, 11, 22, and 25 had been 
found to contain artificial coloring matters, whereas the remaining 
specimens were found to contain neither blood nor a soluble dye, the 
solubility in water, color of the aqueous solution, and conduct 
towards alkaline phenolphthalin, with and without hydrogen peroxide, 
being the only means employed in arriving at these conclusions. In 
