282 INFECTION AND IMMUNITY 



see, we believe that the sensitizing antibody, whether in the process 

 of lysis, agglutination, precipitation, etc., is in all cases the same 

 substance. 



Agglutination. Although Metchnikoff 11 and Charrin arid Roger 12 

 had noticed peculiarities in the growth of bacteria when cultivated 

 in immune sera, which were unquestionably due to agglutination, 

 the first recognition of the agglutination reaction as a separate 

 function of immune sera was the achievement of Gruber and Dur- 

 ham. While investigating the Pfeiffer reaction with B. coli and 

 the cholera vibrio, Gruber and Durham 13 noticed that if the respec- 

 tive immune sera were added to bouillon cultures of these two 

 species, the cultures would lose their turbidity and flake-like clumps 

 would sink to the bottom of the tube, the supernatant fluid becom- 

 ing clear. Gruber, at the same time, called attention to the fact 

 that immune sera would affect in this way not only the microor- 

 ganism used in their production, but, to a less energetic extent, 

 other closely related bacteria as well. 



Widal, very soon after Gruber and Durham's announcement, 

 applied the agglutination reaction to the practical diagnosis of 

 typhoid fever, finding that the serum of patients afflicted with this 

 disease showed agglutinating power over the typhoid bacillus at 

 early stages in the course of the fever. The reaction, thus practically 

 applied to clinical diagnosis, was soon shown to be of great im- 

 portance in its bearing on bacteriological species differentiation. 

 Since animals immunized against a definite species of bacteria ac- 

 quire in their sera specific agglutinating powers for these bacteria 

 and at best only slight agglutinating powers for other species, im- 

 mune sera can be used extensively in differentiating between bac- 

 terial varieties. 



Agglutination may be observed microscopically or macroscopic- 

 ally. Bacteria brought into contact with agglutinating serum in 

 the hanging drop rapidly lose their motility, if motile, as in the 

 case of typhoid bacilli, and gather together in small clumps or 

 masses. The microscopic picture is striking and easily recognized 

 and the reaction takes place with varying speed and completeness, 

 according to the strength of the agglutinating scrum. 



11 Metchnikoff, "Etudes sur I'lmmunite," IV Memoir, 1891. 



12 Charrin et Eager, Compt. rend, de la soc. de biol., 1889. 



13 Gruber und Durham, Munch, med. Woch., 1896. 



