FIXATION OF THE COMPLEMENT 233 



valuable method of diagnosis for infective diseases which is known as the 

 Bordet-Gengou or complement-fixation reaction. The reaction has been 

 applied by Widal and Le Sourd to the diagnosis of enteric fever (fixation 

 reaction, hsemolyso-diagnosis) and is applicable to the majority of micro- 

 organic diseases. Two different cases arise for consideration. 



First case. Given a serum suspected to contain a particular immune body, 

 the serum of an enteric fever patient, for example, a certain diagnosis may 

 be made by the complement-fixation method. 



Heat the serum to 55 C. for half an hour, prepare a mixture of typhoid 

 bacilli and the heated serum, add some complement and incubate the mixture 

 at 37 C. for an hour. Then add a mixture of red cells and homologous 

 inactivated hsemolytic serum and incubate again. One of two things may 

 happen. 



1. Either the typhoid bacillus is sensitized by the inactivated suspected 

 serum, in which case it fixes the complement so that on the addition of 

 sensitized red cells there being no free complement the cells do not undergo 

 haemolysis. If this takes place it may be affirmed that the suspected serum 

 contains antibodies for the typhoid bacillus and that the patient is suffering 

 from enteric fever. 



2. Or the typhoid bacillus is not sensitized by the suspected serum and 

 therefore does not combine with the complement, so that on the addition of 

 sensitized red cells the free complement attaches itself to them and haemolysis 

 is the result. The suspected serum, therefore, in this case contains no typhoid 

 antibodies. 



Second case. Suppose a given organism is believed to be the typhoid 

 bacillus and it is desired to confirm the diagnosis. 



Prepare a mixture containing the suspected bacillus, heated antityphoid 

 serum and complement. Incubate for an hour and then add a mixture of 

 red cells and inactivated haemolytic serum. 



1. The bacillus may be sensitized by the antityphoid serum in which case 

 it will absorb the complement, and on the addition of sensitized red cells 

 there being no free complement no haemolysis takes place ; the complement 

 was deviated or fixed by the suspected bacillus which is therefore the true 

 typhoid bacillus. 



2. The bacillus may not be sensitized by the antityphoid serum conse- 

 quently it cannot fix the complement and this remaining in solution is free 

 to combine with the sensitized red cells. There had been no fixation of the 

 complement so haemolysis occurs ; the bacillus therefore, not uniting with 

 the antityphoid immune body, is not the typhoid bacillus. 



The value of this method of diagnosis to the bacteriologist can be easily 

 appreciated : the results are more constant and more delicate than those 

 obtained by means of agglutination tests but considerable technical skill is 

 required in carrying out the reaction. 



Technique of the complement-fixation reaction. 



The following materials are required : 



Apparatus, etc. 1. A number of narrow test-tubes about 10 cm. long and 

 5 c.c. capacity. 



2. A number of 1 c.c. pipettes graduated in tenths of a cubic centimetre. 

 (Levaditi's pattern is, perhaps, the best (fig. 160).) 



The various manipulations should as far as possible be conducted under 

 aseptic conditions, so that the tubes and pipettes must be sterilized in the 

 hot air sterilizer. 



