176 TECHNIQUE OF THE COMPLEMENT FIXATION METHOD 



b. Same with Diminishing Amounts oj Serum. 



With 0.25 c.cm. of antigen the titer of this meningococcus serum is 0.0005 c.cm. of 

 serum. One could with this constant quantity of serum, and varying quantities of 

 antigen, titrate the minimum amount of antigen necessary for complement fixation. 

 It would even be preferable for such a test to employ 0.005 c - cm - of tne serum, as this 

 amount surely binds no complement. If such a titration is undertaken it will be found 

 that 0.005 c - cm - of serum with 0.05 c.cm. of extract can bind o.i c.cm. of complement. 



Similarly the antibodies contained in the blood serum or spinal fluid of a 

 patient can be determined by means of complement fixation. 



If it is desired to demonstrate the antigen instead of antibody, one pro- 

 ceeds as follows: 



