20 
upon the nature of the oxidizing substance employed, and certainly 
to a great extent on the general technique of the operation and the 
skill and experience of the operator. In the following paragraphs I 
have summed up the principal facts concerning the delicacy of the 
chemical tests for blood with each of the several chromogenic sub-* 
stances which have been most extensively employed for this purpose. 
GUAIACUM. 
Aschern (8) was able to recognize 1 part of blood to 2,000; Adler 
(2), 1 part to 5,000; Bullard (31), 1 drop of blood in 6 ounces of water; 
Fahrner (52), 1 c. c. of blood to 20 c. c. of water; Huhnefeld (73), 1 
part of blood to 6,000. According to this last-named author, the 
blood of even a flea spot which is very old can be recognized, and he 
was also able to prove the presence of hemoglobin in the 3-day-old 
embryo of the chick by means of his method of carrying out the guaia- 
cum test. Breteau (25) observed that a solution of hemoglobin in 
tartaric acid so dilute as to be entirely colorless gave a blue color with 
guaiacum and old oil of turpentine, even after boiling; and Liman 
(105) was able to detect blood at a dilution of 1 to 40,000 by means of 
guaiacum. Schaer (140) describes the guaiacum test as remarkably 
delicate, and according to Siefert (170) a few milligrams of blood are 
sufficient for the test. Bertolet (18) has adapted the guaiacum test 
to the microscopic examination for blood, and Schuster (165) cites 
Vitali to the effect that blood gives the guaiacum test at the extraor- 
dinary dilution of 1 part to 100,000 million; this, if true, refers prob- 
ably to a microscopic modification of the test. Schumm (161) was 
able to recognize blood by means of the guaiacum test at a dilution of 
1 to 40,000 to 100,000, and in urine, 1 part of blood in 20,000 to 40,000 
parts of urine. 
Clement (37) was able to detect 1 drop of blood in 100 grams of 
water by means of guaiacum. Babcock (10) found the sensitiveness of 
the guaiacum reaction to be about 1 part of blood to 4,000. Jaworski 
and Korolewicz (75) detected 1 part of blood in 25,000 in feces, but 
failed to find it at a dilution of 1 to 100,000. Friedmann (58) de- 
tected 1 drop of blood in 100 c. c. of urine and 1 drop of blood in 500 
c. c. of gastric contents ; he detected 2 drops of blood in 50 grams of 
feces and 100 c. c. of water by filtering and testing the filtrate. In 
uncooked milk he detected 1 drop of blood in 430 c. c., and in cooked 
milk 2 drops in 100 c. c. ; in pleuritic exudates, 3 drops of blood in 
100 c. c. According to Fraenkel (57) 2.5 to 3 percent of blood in 
feces can be recognized by Weber’s test. He also obtained distinct 
reactions with blood at a dilution of 1 to 100,000. 
