94 APPLIED IMMUNOLOGY 



by the bacterial system, none being left free to act in 

 connection with the hsemolytic system. 



In a second experiment, exactly the same compon- 

 ents were used, except that the cholera-immune serum 

 was replaced by normal serum. Hence, complement 

 was not fixed by the bacterial system, but remained 

 free to become a part of the hsemolytic system, and 

 haemolysis occurred. 



The first or positive and the second or negative re- 

 actions may be graphically illustrated thus : 



1. Positive Result 



Suspension of cholera spirilla Haemolytic serum No 



^ v^ haemolysis 



X _^^,,^ Complement 



Cholera-inamune serum '^''''''^ Red corpuscles 



2. Negative 



Suspension of cholera spirilla Haemolytic serum 



Complement ^ Haemolysis 



^^ T 



Normal serum Red corpuscles 



The specific complement-fixation reaction may be 

 applied to the diagnosis of several diseases. By test- 

 ing an unknown serum with a known bacterial anti- 

 gen, it is thus possible to determine whether or not the 

 individual furnishing the serum is infected by the par- 

 ticular organism from which the antigen is made. For 

 some time after Bordet and Gengou's announcement, 

 the reaction had chiefly a scientific rather than a prac- 

 tical interest. The first great advance toward render- 

 ing the method of practical importance was the dis- 



