COMPLEMENT FIXATION 393 



of a vulgar fraction of which the numerator is the 

 number recorded for the specific serum. This fraction, 

 expressed as a percentage of unity = the opsonic index. 



IMMUNE BODY. 



Immune body or amboceptor is the name given to a 

 substance present in the serum of an infected animal 

 that has successfully resisted inoculation with some par- 

 ticular micro-organism, and which possesses the power 

 of linking the complement normally present in the 

 serum to bacteria of the species used as antigen in such 

 a manner that the micro-organisms are rendered in- 

 nocuous, and ultimately destroyed. The presence of 

 the immune body in the serum can be demonstrated 

 in vitro by the reaction elaborated by Bordet and Gen- 

 gou, known as the complement fixation test, the exist- 

 ence or the absence of the phenomenon of complement 

 fixation being rendered obvious macroscopically by the 

 absence or presence of haemolysis on the subsequent 

 addition of "sensitised" red blood corpuscles, (e.g., a 

 mixture of erythrocyte solution and the appropriate 

 haemolysin two of the three essentials in the haemoly- 

 tic system, vide page 326). 



Apparatus Required: 



Sterile pipettes i c.c., (graduated in tenths). 



16X2 cm. test-tubes. 



9X1 cm. test-tubes. 



Test-tube racks for each size of test-tube. 

 Reagents Required: 



Normal saline solution. 



Erythrocyte solution (human red cells, page 329) =E. 



Haemolytic serum (for human cells) = H.S. 



Complement (fresh guinea-pig serum) =C. 



Specific serum from inoculated animal, inactivated = S.S. 



Control pooled serum from normal animals of same species, 

 inactivated = P.S. 



Antigen (cultivation upon solid medium of the organism (e.g., B. 

 typhosus) which has already served as antigen in the inoculation 

 of the experimental animal) =A 



