496 THE TECHNIC OF COMPLEMENT-FIXATION REACTIONS 



0.3 c.c. of this dilution ( = 0.03 c.c. undiluted serum). In performing 

 the main test double this quantity, or 0.6 c.c., would be used. 



TABLE 19. TITRATION OF AN IMMUNE SERUM 



Each antiserum is tested in a similar manner. In forensic blood 

 tests an antihuman serum is, of course, employed first; if this is negative 

 and it is desirable to determine the source of the blood, other antiserums, 

 so that the ox, horse, dog, etc., are prepared, titrated, and tested with a 

 solution of the blood-stain. 



The Blood-stain. It is first necessary to ascertain that the stain is a 

 blood-stain; this is done by performing the hemin crystal test (p. 303). 

 The stain is then extracted in normal saline solution, as described on 

 p. 304. A 1 : 1000 dilution is made approximately by so diluting the 

 extract that it just gives a slight opalescence when boiled with a few 

 drops of acetic acid, and a slight foam persists after shaking. Unless 

 it is perfectly clear, it should be filtered. 



