24 
Curtman (42) states that the guaiacum test is not sure for the presence 
of blood if positive, but that it is a favorite test with many authors. 
Gallaher (59) says that the guaiacum test is the best and surest, and 
that when the test is applied as directed and a blue color instantly 
obtained, the existence of blood in the liquid is demonstrated beyond 
a doubt. Ascarelli (7) finds the benzidin test to be more useful and 
sensitive than the guaiacum test. A negative test certainly means 
the absence of blood and even a positive test can be looked upon as 
undoubted evidence of the presence of blood. Einhorn (49) says 
finally : 
I do not hesitate to recommend benzidin paper as a useful method for the detection 
of blood in stomach contents, urine, and feces. 
Delearde and A. Benoit (16) regard phenolphthalin as a very delicate 
reagent for blood; on the other hand, Pozzi-Escot (128) regards it as 
altogether untrustworthy for the reason that similar reactions are 
obtained with a large number of substances. 
The general consensus of opinion among those who have given this 
subject their attention would seem to be, therefore, that the guaiacum 
test for blood and similar color reactions are valuable especially if 
they lead to negative results, as proving beyond the peradventure of 
a doubt that blood is absent. On the other hand, if a positive test 
is obtained, care should be taken to exclude oxidases or peroxidases 
by boiling, and the salts of the heavy metals and other oxidizing 
agents b}^ chemical methods, and, if possible, to subject the material 
under investigation to confirmative tests for blood before finally 
concluding that blood is present. 
PHENOLPHTHALIN AS A REAGENT FOR BLOOD. 
Phenolphthalin, or dioxy-triphenylmethane carbonic acid, is the 
leuco-compound of phenolphthalein, and on oxidation it is converted 
into the latter compound in the sense of the equation, C 2 oHi 604 + 0 = 
C 20 H 14 O 4 + H 2 O. Pure phenolphthalin itself is colorless in alkaline 
solutions, but on adding alkali to the substance after oxidation, or 
if it be oxidized in the presence of alkali, there results the deep pur- 
ple-red coloration characteristic of phenolphthalein in alkali. 
Several years ago Kastle and Shedd (83) showed that a neutral 
solution of the sodium salt of phenolphthalin can be employed as a 
reagent for the oxidases. In 1903, Meyer (114) employed phenol- 
phthalin as a reagent for the leucocytes. By means of this reagent 
he was able to determine not only the extent of the leucocytosis in 
certain pathological conditions, but also the character of the leu- 
cemia, and he proposed to employ it, instead of the leucocyte count, 
in arriving at the number of leucocytes in the blood. In the same 
yearUtz (191) recommended a solution of phenolphthalin in sodium 
carbonate as a reagent for blood in forensic investigations, and 
