BA CTERIOL YSINS A ND H&MOL YSINS 115 



Gonococcus antigen+Gon. Anti-serum = Reaction ; 

 " " +Any other Anti-serum = No re- 



action ; 



+ Gon. Anti-serum + Comple- 

 ment = Reaction ; 

 +Any other Serum + Comple- 

 ment = No Reaction. 



It is now evident that it is not only possible to 

 determine if a serum contains antibodies, but it is 

 also possible to tell how much of these antibodies 

 it contains by simply adding to the serum some of 

 its antigen and a known amount of complement. 

 If the serum contains no antibodies, no comple- 

 ment will be absorbed. If it contains a large 

 amount then a large amount of complement will 

 be absorbed. The test, therefore, is a quantitative 

 test for the fixation or absorption of complement. 

 Inasmuch as the absorption or fixation does not, in 

 any way, alter the appearance of the serum, it is 

 not possible to tell simply by observation, whether 

 or not, the complement has been absorbed. There- 

 fore, some indicator must be used which will show 

 when complement has been absorbed and when it 

 has not. An indicator which will change color in 

 the presence of complement and remain unchanged 

 when the complement has been absorbed will show 

 in a very definite manner, when a reaction has 

 taken place. With such an indicator it is a simple 



