THE COMPLEMENT FIXATION TEST 325 



EXERCISE 14. TO DEMONSTRATE THE COMPLEMENT 

 FIXATION TEST 



The complement fixation test is one of the most com- 

 plicated biological reactions used as a means of diagnosis 

 in infectious diseases. 



Apparatus. Guinea pig; rabbit; sheep; suspected 

 serum (from aborting cow or other animal to be tested); 

 small test tubes; test-tube rack; flasks; physiological 

 salt solution; centrifuge tubes; disinfectant; syringe and 

 needles. 



Culture. Bad. abortus (or other organism depending 

 on disease for which test is made). 



I. TITRATION OF REAGENTS 



Method. Four reagents other than the serum to be 

 tested are required: 1, complement; 2, hemolysin; 3, red 

 blood cells from a sheep; 4, antigen. Above components 1, 

 2 and 4 must be titrated before using in order to deter- 

 mine the amounts to be used in the tests. 



1. Complement. This is contained in and obtained from 

 fresh serum from a guinea pig. The complement is titrated 

 for the purpose of determining the least amount which in 

 the presence of a sufficient amount of hemolysin will produce 

 complete hemolysis of a definite quantity of washed red 

 blood cells from the sheep. This amount is spoken of as 

 the litre. 



2. Hemolysin (see Exercise 13). The source of hemo- 

 lysin is inactivated serum from a rabbit that has been 

 previously immunized to washed red blood cells from a 

 sheep. 



The selection of a rabbit and sheep is merely a matter 

 of convenience. Any two animals of a different genus 

 may be used. In the test for syphilis in man, human 

 blood cells are usually used because more convenient to 

 obtain in a number of laboratories. 



