7 
in this connection he cites the fact that neither putrefaction nor boil- 
ing destroy the activity of solutions of blood corpuscles, which would 
indicate that their power to activate oxygen depends less on their 
organization than on their iron content. He is careful to point out, 
however, that certain iron-free organic substances, among them ben- 
zaldehyde, also possess the power of converting inactive oxygen into 
the active form and thereby accomplish oxidations which can not be 
brought about by ordinary oxygen. 
In a still later communication (151) he considers these phenomena 
in their relation to oxidation processes in the animal organism, and 
points out the importance, to the respiratory process, of the oxygen- 
carrying power of the blood corpuscles and their correlated property 
of actively decomposing hydrogen peroxide, as a means whereby 
the inactive oxygen of the atmosphere is rendered available for the 
requirements of the organism. He also calls attention to the delicacy 
of the guaiacum-hydrogen peroxide test for blood and to its value in 
forensic investigations, and later he observed that dried blood cor- 
puscles are more active than the fresh material, so far as their power 
of inducing oxidation is concerned. 
Our knowledge of the guaiacum test for blood has been considerably ■ 
extended by the investigations of van Deen, Day, Taylor, Liman, and 
others ; and in medical writings, despite the earlier work of Schoen- 
bein, the test has generally come to be known as the van Deen test, or 
among certain English authors, as the Day test. 
According to van Deen (193) the smallest quantity of blood, no 
matter how old it may be or how mixed with other substances, is col- 
ored blue by tincture of guaiacum and an ozone-carrier, such as oil of 
turpentine. That such is the case is indicated by the following: 
First, a very small quantity of old, stinking blood, which had stood 
eight or nine months, was greatly diluted with distilled water so that 
the liquid was nearly colorless. Oil of turpentine and then tincture of 
guaiacum were added to this, and an intense blue color soon devel- 
oped. This blue color also develops on allowing the blood to stand 
for twenty-four hours with oil of turpentine and then adding the 
guaiacum. On the other hand, if the mixture is filtered, the guaiacum 
is then without action on the filtrate, for the reason that the turpen- 
tine does not pass through the filter and the blood does not take 
up the ozone contained therein, which it is necesssary to add to 
the guaiacum. Second, blood which had stood for two years with 
glacial acetic acid was diluted with distilled water until the solution 
was nearly colorless. To this there were then added 2 drops of 
oil of turpentine and tincture of guaiacum; the mixture took on a 
blue color. Third, still more glacial acetic acid was added to the 
blood used in Experiment No. 2, and the solution filtered. A small 
amount of the filtrate still gave a blue color with oil of turpentine 
