21 
ALOm. 
According to Buckmaster (29) aloin is less sensitive thanguaiacum, 
but more stable. Schaer (141) has also found that the color pro- 
duced with alom is more stable than that obtained with guaiacum. 
BENZIDIN. 
According to Utz (192) benzidin is sharper than guaiacum, and 
Schumm (163, 164) describes benzidin as a delicate reagent. Adler 
(2) ’Sicas able to detect blood at a dilution of 1 to 100,000 by means of 
benzidm, and Schumm (159) at a dilution of 1 to 200,000. I have 
also found benzidin to have nearly the same delicacy as phenol- 
phthalin, especially as practically applied to the examination of ani- 
mal fluids for blood, the difference between the two reagents being 
that phenolphthalin 3 flelds a more stable and permanent color 
(phenolphthalein) than benzidin. This has certain advantages. 
Ascarelli (7) gives the delicac}^ of benzidin as a reagent for blood 
as 1 to 300,000, or in practice 1 to 250,000, and with benzidin paper, 
1 part to 80,000; at a dilution of 1 to 120,000 the paper failed to give 
the test. 
According to Schumm (163) the delicac}^ of the benzidin test for 
blood depends on the purity of the reagent. With 14 of Merck’s 
preparations the limit of the reaction was about 1 part of blood to 
200,000, and with two others about 1 part to 50,000. Mhth two of 
Kahlbaum’s preparations the limit of the reaction was about 1 part 
to 2,000,000 and with others about 1 part to 50,000. 
THE LEUCO-BASE OF MALACHITE GKEEN. 
Adler (2) found this chromogenic substance to have about the 
same delicacy" as benzidin, viz, 1 part of blood to 100,000. Cz^dilarz 
and Von Fiirth (43) also speak of it in the highest terms as a reagent 
for measuring the ox^^gen-carrAflng power of blood. 
PHEXOLPHTHALIX. 
Utz (191) regards phenolphthalin as a more delicate and useful 
reagent than either guaiacum or aloin, and found that blood spots 
2 square millimeters in area gave the reaction rapidU and with cer- 
tainty. Delearde and A. Benoit (16) found phenolphthalin to be 
more sensitive than guaiacum, and by means of it were able to detect 
blood at a dilution of 1 to 1,000,000. I have found it possible to 
recognize blood at a dilution of 1 part to 80,000,000 hj means of 
phenolphthalin. (See page 30.) 
