a0, Occult Blood in Stools 
Determination of the Sensitiveness of the Above Procedure. 
To this end a series of standard blood solutions was prepared 
as follows: 
Solution A.—1 cc. of freshly drawn human blood was diluted 
to 100 ce. in a volumetric flask with distilled water. A few drops 
of toluene were added as a preservative. 1 cc. of this solution 
contained 0.01 cc. of blood. 
Solution B.—1 cc. of Solution A was made up accurately to - 
10 ce. giving a solution of strength 1 ec. = 0.001 cc. of blood. 
Solution C.—1 ec. of Solution A was diluted to 20 ec., yield- 
ing a solution of strength 1 cc. = 0.0005 ce. of blood. 
Solution D.—1 cc. of Solution A was diluted to 30 ecc., giving 
a solution the strength of which was 1 ce. = 0. 0008 ce. of blood. 
Stools Employed in the Tests. 
The stools used in the following tests were obtained from patients 
kept on a meat-free and soup-free diet. They were all formed 
stools and when tested by the procedure already mentioned gave 
negative results. 10 gm. of a negative stool were weighed in a 
beaker, about 50 cc. of water added, and thoroughly mixed; the 
mixture was then made up with water to 100 cc. and again uni- 
formly mixed. Separate 10 ce. portions of this mixture were re- 
spectively treated with definite volumes of the above standard 
blood solutions, thoroughly mixed, and heated to boiling for 10 
minutes with occasional stirring on a hot plate. After cooling, 
the mixtures were stirred for 5 minutes with 3 cc. of glacial acetic 
acid and 12 ec. of ether. 2 cc. portions of the clear extracts were 
transferred to test-tubes, and treated with 0.5 cc. of guaiaconic 
acid solution and five drops of perhydrol. The following results 
were obtained. 
The experiments in Table I were repeated three times, using dif- 
ferent negative stools for each series, with the same results. It ap- 
pears therefore that when 1 gm. is taken for the test our technique 
is capable of detecting 0.0001 ce. of blood or one part in 10,000. 
It may be of interest to note that when 1 cc. of 3 per cent 
medicinal hydrogen peroxide was used in place of the five drops 
of 30 per cent perhydrol, very faint and in some cases negative 
