232 THE ANTIOEN-ANTIBODY REACTIONS 



among the reducing agents that reactivate oxidized complement, and there appears to 

 be a variable relation between the two, whose nature is as yet obscure. 



The hypothetical dietary deficiency in complement-poor guinea-pigs associated with 

 lack of green food may conceivably be a vitamin K deficiency, for Busing and Zuzack 

 (1943) report a marked correlation between the complement titre and vitamin K intake 

 in the young chick. 

 Complement in Other Animals. 



The greater part of the work on complement has been concerned with guinea-pig 

 serum. The quantitative and qualitative variations in complement among different 

 species of animal have received little study. Shrigley and Irwin (1937) found no associa- 

 tion between hsemolytic and bactericidal activity in guinea-pig, sheep or rabbit sera, 

 but noted a wide species variation of both. Ecker, PiUemer and Kuehn (1942) fractionated 

 the sera of man, dog, cat, guinea-pig, monkey, rabbit and sheep, and found wide species 

 differences in the effect on opsonic powers of measures designed to inactivate or remove 

 each of the four components. No generahzation about complement titres in mammals 

 is possible without specifying the components present, and the method of measuring the 

 complement — e.g. bactericidal or haemolytic — and it must be remembered that in all 

 cases the titre is determined by the amount of the least plentiful component. In human 

 sera, for example, it is C'2 (Hegediis and Greiner 1938, Heidelberger and Mayer 1942) 

 and to some extent C'3 (Dozois, Seifter and Ecker 1944). Mouse serum, which has no 

 complementary activity, lacks C'2 (Brown 1943). 



Complement Fixation. 



We have noted that the absorption of complement is a general property of 

 bacterial cells that have been sensitized by a specific antibody ; though some 

 bacteria undergo lysis as a result of this absorption, while others do not. That 

 complement fixation, apart from the observation of any resulting change in the 

 bacterial cells, could be used as a general method for the detection and titration of 

 specific antibodies was first demonstrated by Bordet and Gengou (1901). In these 

 experiments a suspension of a given bacterium was allowed to react with a specific 

 antiserum in the presence of complement. After time had been allowed for the 

 reaction to take place, red cells and a suitable dilution of hsemolysin were added, 

 and the mixture was incubated again for 1 hour at 37° C. It was found that in 

 these circumstances no lysis took place, showing that no free complement was 

 present, and it was reasonably inferred that it had been absorbed by the bacterium- 

 sensitizer complex. 



The. reaction may be summarized as follows: 



(a) Bacteria + Sensitizer -j- Complement = Fixation. 

 (6) (a) + Red Cells -|- Hsemolysin = No haemolysis. 



It will be noted that (6) is simply an indicator reaction. It has no connection 

 with the fixation of complement by the sensitized bacteria. That reaction has 

 already occurred in (a). 



Using this technique Bordet and Gengou demonstrated sensitizers for Past, 

 pestis, B. anthracis, Salm. typhi, the bacillus of swine plague, and Proteus vulgaris 

 in the corresponding antisera. 



The following year Gengou showed that the same phenomenon occurs when 

 soluble proteins are allowed to react with their specific antisera in the presence of 

 complement. He demonstrated specific complement fixation, using as antigens 

 cow's milk, egg-white, horse fibrinogen, and heated dog serum, and as antibody in 

 each case the serum of a rabbit which had been immunized against the corre- 

 sponding protein. 



