TECHNIC OF PRECIPITIN REACTIONS 



307 



hind the tubes aids greatly in the detection of the finer degrees of opal- 

 escence or precipitation. 



Preliminary Titrations. The precipitin content of an immune serum 

 is titrated frequently during the process of immunization and after the 

 animal has been bled. For medicolegal purposes, Uhlenhuth advises 

 the use of only highly valent serums. He considers an antiserum ef- 





FlG. 90. TlTRATION OF A PRECIPITIN (SERUM). 



Not all tubes of the series are here shown. Note the well-marked precipitate in 

 the bottom of the first two tubes (1 : 100 and 1 : 500); the third tube (1 : 1000) 

 shows less precipitate; the fourth tube (1 : 2000) is negative (clear and no precipi- 

 tate). The titer of this serum was recorded as 1 : 1000. 



ficient if 0.1 c.c. of it, when added to its respective serum-antigen 

 diluted 1 : 1000, produces a distinct turbidity, either at once or in from 

 one to five minutes at the latest. 



Into a series of six test-tubes place 2.0 c.c. of the following dilutions 

 of serum-antigen, prepared with normal salt solution: 1:100, 1:500, 

 1:1000, 1:2000, 1:5000, and 1:10,000. To each tube add 0.1 c.c. of 



