OPSONINS, AGGLUTININS, PRECIPITINS, LYSINS 141 



that the complement is not specific but is present in normal 

 blood. 



Bordet and Gengou found that bacteria or red blood cells 

 could be " sensitized " by placing them in immune serum that had 

 been' deprived of its complement ; that is, the antigen and ambo- 

 ceptor could enter into a loose combination without the former 

 being affected. If, now, measured amounts of fresh serum from 

 a non-treated animal be added, all the complement contained in 

 it is " fixed " or absorbed, with the result that these sensitized 

 bacteria or red blood cells are dissolved. These facts, which 

 emphasize the general law that when an antibody is demonstrated 

 it may be assumed that the antigen is or has been present, form 

 the basis of the Wassermann reaction for syphilis and the comple- 

 ment fixation tests for gonococcus infection, streptococcus infec- 

 tion, etc. 



Thus when in suitable proportions a bacterial antigen (for 

 example, a suspension of gonococci) is mixed with heated serum 

 containing the specific amboceptor (serum of a patient with a 

 gonococcic infection), and fresh serum containing complement 

 (usually that of a guinea pig) is added, there is a union of the 

 antigen and amboceptor, and all of the complement is absorbed. 

 Since there is no visible sign that such a union has taken place, 

 it is determined by adding in measured amounts an emulsion of 

 red blood cells together with their specific amboceptor but no com- 

 plement. The red blood cells will remain unchanged because there 

 is no free complement left to unite with them. 



If, on the other hand, the suspected patient had not a gonorrheal 

 infection and consequently no specific amboceptors were present 

 in his serum, then the complement could not be bound to the anti- 

 gen, so that on the addition of the red blood cells plus their ambo- 

 ceptor the complement would be promptly absorbed by them 

 and hemolysis occur. In this latter case a marked difference in 

 the mixture would be noted ; the disintegration of the envelope 

 of the cells releasing the hemoglobin would give to the fluid a clear 

 red appearance totally different to the opaque pinkish color of 

 the positive case in which the red blood cells remained intact. 



