220 MICROBES AND TOXINS 



true is it that it is the antigen-antibody compound which 

 absorbs the complement. Although the complement of one 

 animal species may differ from that of another species, yet in 

 a given serum, in opposition to Ehrlich's theory, there exists but 

 one complement or rather one complementing property (exp. 

 of Bordet, Gay, Muir and Browning, etc.). It is due to 

 Bordet's correct attitude on these points that the Bordet- 

 Gengou reaction (complement fixation) has been capable of 

 such successful application in various bacteriological diagnostic 

 methods, and recently by Wassermann in the diagnosis of 

 syphilis. 



Finally, since the complement attaches itself, not to the 

 immune body, but to the antigen-antibody combination, there 

 is no reason to suppose the existence of a haptophore group 

 of the " complementophile " kind, indispensable to the 

 immune body if complement is to be fixed. This question 

 has for some time been a sort of test for the side-chain 

 theory, and it seems to have resulted in favour of Bordet's 

 ideas. ^ 



From the beginning of his researches in 1896, Bordet has 

 imagined immunity reactions, not as chemical combinations, 

 but as physical phenomena of absorption or molecular adhesion. 

 He considered that in agglutination (where the bacteria are 

 passive, since dead bacteria also agglutinate) serum acts by 

 modifying the relations of molecular attraction between the 

 bacteria and the fluid bathing them, and that, in the first 

 phase of the phenomenon at least, the bacteria behave like 

 particles in general. Under the influence of Duclaux's ideas, 

 he observed the resemblances between agglutination and 

 coagulation. From the point of view of their coagulating and 

 dissolving properties, he compared the active sera to the 

 digestive juices, and, like Metchnikoff and after him Ehrlich, 

 he also saw in immunity, though from a different point of 

 view, a particular case of the physiology of digestion. 



At that time the results of the study of colloids had 



^ Experiments of Ehrlich and Sachs, of Sachs and Bauer ; of Bordet 

 and Gay and Bordet and Streng on haemolysis by ox-serum. 



