102 



LABORATORY COURSE IN SERUM STUDY 



(bacterial and others) in the presence of their specific antisera 

 will fix complement so that the subsequently added red cells 

 sensitized by their appropriate hsemolytic immune-body will fail 

 to be laked, because no free complement is available. Neither the 

 antigen alone nor the antibody alone will fix complement in this 

 manner. 



Unfortunately bacterial cell bodies (like many other sub- 

 stances) if in sufficiently large amounts will of their own accord, 

 probably for purely physical reasons, absorb complement, in a 

 non-specific way, i.e., without the presence of a specific antibody. 



The immune sera likewise have often the power of absorbing 

 complement in a non-specific way in the absence of antigen and 

 this power must be determined by preliminary titration in order 

 that allowance may be made for it in the main test. 



For this reason before doing a Bordet-Gengou reaction (and, 

 as will be seen later, in all complement fixation work) it is neces- 

 sary to determine the degree to which such non-specific comple- 

 ment fixation will take place with the given antigen and to use 

 in the actual test an amount too small to give such a false reaction. 



Experiment 1 



PRELIMINARY DETERMINATION OF THE NON-SPECIFIC BINDING POWER 

 OF THE BACTERIAL ANTIGEN 



Emulsify a 24 hour slant of typhoid bacilli in 10 c.c. of saline solu- 

 tion. Heat at 56 C for 30 minutes. 



1 Determined by preliminary titration 



Add sufficient saline solution to each tube so that the final volume 

 after adding red cells and amboceptor shall equal 2.5 c.c. Incubate one 

 hour in water bath. Add 0.5 c.c. of 5% reel cell suspension plus two 

 units of amboceptor to each tube. Incubate for one half hour in water 

 bath. 



