BLOOD AND LYMPH 261 



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 atitiserum used in this test is 

 prepared by injecting 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 examina- 

 tion in the proportion of 1:100 and place the mixture at 37C. 

 If human blood is present in the solution a turbidity will be noted 

 and this will change within three hours to a distinctly flocculent 

 precipitate. This antiserum will react thus* with no other known 

 substance. 



Of the other five blood tests mentioned the last two named are 

 generally considered to be the most satisfactory. They give equally 

 reliable results with fresh blood and with blood from clots or stains 

 of long standing, provided the latter have not been exposed to a high 

 temperature or to the rays of the sun for a long period. The technic 

 of the tests is simple and the formation of the dark brown or chocolate- 

 colored crystals of hemin or the production of the green or 

 blue color with benzidine is indisputable proof of the presence of blood 

 in the fluid, clot or stain examined. The weak point of the tests, 

 medico-legally, lies in the fact that they do not differentiate between 

 human blood and that of certain other species of animal. 



The guaiac test (see page 265), although generally considered less 

 accurate than the hemin test, is held by some to be a more delicate test 

 than the hemin test, if properly performed. One of the most common 

 mistakes in the manipulation of this test is the use of a guaiac solution 

 which is too concentrated and which, when brought into contact with 

 the aqueous blood solution, causes the separation of a voluminous 

 precipitate of a resinous material which may obscure the blue colora- 

 tion; this is particulary true of the test when used for the examination 

 of blood stains. A solution of guaiac made by dissolving i gram of the 

 resin in 60 c.c. of 95 per cent alcohol is very satisfactory for general use. 

 The test is frequently objected to upon the ground that various other 

 substances, e.g., milk, pus, saliva, etc., respond to the test and that it 

 cannot therefore be considered a specific test for blood and is of value 

 only in a negative sense. We have demonstrated to our own satisfac- 

 tion, however, that many samples of milk give the blue color upon the 

 addition of an alcoholic solution of guaiac resin without the addition of 



