236 



FIXATION OF THE COMPLEMENT 



The bacillary emulsion should be titrated by placing in the incubator at 

 37 C. a series of tubes containing progressively increasing quantities of the 

 emulsion, an haemolytic couple (p. 232) and some complement. 



Examination of the table shows that the quantity of bacterial emulsion 

 to be used must be the amount contained in tube 3 or tube 4, namely 0*2 

 or 0'3 c.c. these being the maximum doses which do not prevent haemolysis 

 taking place. 



In the serum diagnosis of syphilis, as it is not possible to obtain a culture 

 of the treponeme, various other substances are used as the antigen, e.g. an 

 extract of the liver of a syphilitic foetus. This will be referred to later 

 (vide Chap. LIV.). 



Bacteriolytic serums. Bacteriolytic serums are obtained either from 

 immunized animals or from man. A small quantity of blood 4 to 5 c.c. is 

 sufficient and may be obtained in the case of the human subject by puncture 

 of a vein at the bend of the elbow or with the aid of a Bier's cupping glass ; 

 in the case of the rabbit by puncturing an ear vein (p. 194). After being 

 collected the blood is put aside for a few hours, and the serum is then pipetted 

 off and heated in sealed tubes at 55 C. for half an hour to destroy the com- 

 plement. In carrying out the experiment the bacteriolytic serum should 

 be added to the emulsion of bacteria in sufficient quantity to sensitize them 

 but the actual amount required for sensitization should not be greatly exceeded 

 for fear of introducing errors. The serum can be titrated by a method similar 

 to that used for titrating the antigen (vide ante). 



Experimental details. The reagents being prepared, assume that it is 

 desired to determine whether a given vibrio is the cholera vibrio or not. 

 The experiment will be carried out as shown in the table on p. 237. 



In this experiment no haemolysis has taken place in the tubes Nos. 2, 3, 4 : 

 therefore the vibrio under investigation was sensitized by the cholera immune 

 serum and was able to combine with the complement. The organism, there- 

 fore, is the cholera vibrio. 



In tube No. 1 the quantity of vibrio emulsion was not quite sufficient, and 

 this is the reason why the fixation has not been complete. 



Examination of the control tubes confirms the diagnosis by proving that 

 in the absence of anticholera serum in one case and in the absence of the 

 cholera vibrio in the other no fixation has occurred, and therefore the tubes 

 show haemolysis. 



