BLOOD. 193 



able to produce the blue color upon the addition of the guaiaconic 

 acid to milk only when the sample of milk tested was brought from 

 the country in sterile bottles^ and further, that no sample of London 

 milk which he examined responded to the test. In the application 

 of the guaiac test to the detection of blood, he states that he was 

 able to detect laked blood when present in the ratio 1:5,000,000 

 and unlakcd blood when present in the ratio I : 1,000,000. This 

 author considers the guaiac test to be far more trustworthy than 

 is generally believed. 



Up to within very recent times it has been impossible to make an 

 absolute differentiation of human blood. Recently, however, the 

 so-called " biological " blood test has made such a differentiation 

 possible. This test, known as the Bordet reaction, is founded upon 

 the fact that the blood serum of an animal into which has been 

 injected the blood of another animal of different species develops 

 the property of agglutinating and dissolving erythrocytes similar 

 to those injected, but exerts this influence upon the blood from no 

 other species. The antiserum used in this test is prepared by inject- 

 ing rabbits with 5-10 c.c. of human defibrinated blood, at intervals 

 of about four days until a total of between 50 and 80 c.c. has been 

 injected. After a lapse of one or two weeks the animal is bled, 

 the serum collected, placed in sterile tubes and preserved for use 

 as needed. In examining any specific solution for human blood 

 it is simply necessary to combine the antiserum and the solution 

 under examination in the proportion of I : 100 and place the mix- 

 ture at 37 C. If human blood is present in the solution a turbidity 

 will be noted and this will change within three hours to a dis- 

 tinctly flocculent precipitate. This antiserum will react thus with 

 no other known substance. 



EXPERIMENTS ON BLOOD. 

 I. Defibrinated Ox-blood. 



1. Reaction. Moisten red and blue litmus papers with 10 per 

 cent sodium chloride solution and test the reaction of the defibri- 

 nated blood. 



2. Microscopical Examination. Examine a drop of defibri^ 

 nated blood under the microscope. Compare the objects you ob- 

 serve with Plate IV, opposite page 184. Repeat the test with a 

 drop of your own blood. 



3. Specific Gravity. Determine the specific gravity of defibri- 

 nated blood by means of an ordinary specific gravity spindle. Com- 



