238 



FIXATION OF THE COMPLEMENT 



and the reaction applied to determine whether a given serum contains anti- 

 bodies for a given organism. In illustration, an example will now be given 

 to show how to determine whether or no the serum of a patient contain 

 typhoid antibodies (hsemolyso -reaction of Widal and Le Sourd). 



In this case the suspected serum after heating at 55 C. is mixed with a 

 known typhoid bacillus and complement. The experiment is arranged in 

 the same way as in the preceding experiment. 



DETAILS OF A COMPLEMENT-FIXATION EXPERIMENT AS ARRANGED FOR THE 

 IDENTIFICATION OF A SUSPECTED ENTERIC SERUM. 



In tubes Nos. 1, and 2 no haemolysis has occurred ; the typhoid bacillus 

 it is evident has been sensitized by the serum under examination, which 

 must therefore have come from a patient infected with the typhoid bacillus. 



Examination of the control tubes shows that the bacillus alone or in presence 

 of normal human serum is unable to fix the complement with the result that 

 haemolysis has taken place. 



If, on the other hand, the serum under investigation had not sensitized the 

 typhoid bacillus haemolysis would have occurred, and the inference would 

 have been that the serum contained no typhoid antibodies. 



Practical applications. 



The method of complement fixation has been applied to the diagnosis of a 

 large number of micro-organic diseases (enteric fever, cholera, dysentery, 

 tuberculosis, etc.) and to the identification of most micro-organisms. It is 

 also the basis of Wassermann's reaction in syphilis which will be considered 

 later (Chap. LIV.). 



