AGGLUTINATION 183 



is based on the fact that the optimum concentration of H-ions which 

 precipitates proteins from solution is characteristic and constant for 

 each protein, and the same is true for the aRglutination of bacteria 

 by acids, the a^shitination by acids beinp; even more sharply specific 

 in some cases than the agglutination l)y immune sera; e. g., typhoid 

 and paratyphoid bacilli are readily distinguished because the former 

 are agglutinated by a concentration of H-ions from 4 to8X10~^, while 

 paratyphoids require 16 to 32X10"^, and colon bacilli are not agglu- 

 tinated at all by acids. The acid agglutination, however, does not al- 

 ways affect all strains in the .same way, some strains which are not 

 readily agglutinable by antisera also resisting acid agglutination.^' 

 According to Arkwright,^'' typhoid bacilli contain two extractable 

 proteins that are agglutinated by acids, one at 3.6X10"^ and the other 

 at 1.1 X 10"^; the former seems to be related to, if not identical with, 

 the substance that is precipitated by immune serum. Apparently 

 acid agglutination of bacteria belongs to the same class of reactions as 

 the coagulation by H-ions of amphoteric colloids of preponderatingly 

 acid character. Bacteria which have been sensitized by serum are 

 more sensitive to acid agglutination than are normal bacteria." 



Alterations in the agglutinability of bacteria are marked, e. g., 

 strains of typhoid bacilH freshly cultivated from human infections 

 may be practically inagglutinable even by active serum, but after pro- 

 longed cultivation on media they may or may not develop agglutina- 

 bilit}^ This phenomenon has not yet been satisfactorily explained, 

 but it may depend on an active immunity of the bacteria against the 

 agglutinins. Such bacteria injected into rabbits produce antisera that 

 will agglutinate ordinary agglutinable strains, but not themselves; 

 hence they do not lack agglutinogens. They give normal complement 

 fixation reactions, and hence do not lack receptors, and they agglu- 

 tinate with acids and chemicals much the same as ordinary agglutin- 

 able strains. ^^ Moreover, identical strains of bacteria grown on media 

 of different composition may show considerable variations in agglu- 

 tinability (Dawson). ^^ 



Conglutination. — Under this term Bordet and Gay described the observation 

 that in ox serum there is a substance wliich combines with corpuscles (or bacteria) 

 that have been acted upon by agglutinating sera, and augments the agglutina- 

 tion.'"' Dean finds that, in general, agglutination requires two agents, one being 

 the specific antibody, and the other a precipitable substance, probably a globulin. 

 When cells have combined with the antibody the precipitable substance is aggre- 

 gated on their surfaces, and, presumably, determines the agglutination. Co-agglu- 

 tination, described by Bordet and Gengou as the agglutination bj' an antigen and 

 the homologous antibody, of the corpuscles of another animal, is probabh- closely 

 related to these phenomena (Dean). 



" See Kemper, Jour. Inf. Dis., 1916 (18), 209. 

 3« Zeit. Immunitat., 1914 (22), 396; Jour. Hyg., 1914 (14), 261. 

 'Mvrumwiede and Pratt, Zeit. Immunitat., 1913 (16), 517. 

 =8 Mcintosh and McQueen, Jour Hyg., 1914 (12), 409. 

 " Jour. Bact., 1919 (4), 133. 



"Literature given bv Dean, Proc. Royal Soc. (B), 1911 (84), 416; Hall, Univ. 

 CaUf. Publ., Pathol., 19i3 (2), 111. 



