AGGLUTINATION 181 



coarse floceuli in soJiitioiis, and probably depends uj)()n alterations in 

 surface tension. 



Bordet-^ made the important observation that agglutination does \ 

 not occur if both the bacterial suspension and the agglutinating serum 

 are dialyzed free from salts before^ mixing; but if, to such mixtures, a 

 small amount of NaCl is added, agglutination and precipitation of the 

 bacteria occur at once. This observation brought the phenomenon of 

 bacterial agglutination into close relation with the precipitation of 

 colloids by electrolytes, Bordet comparing it to the precipitation of 

 particles of inorganic matter suspended in the fresh water of rivers 

 that occurs when the fresh water meets the salt water of the ocean. 

 He found that the agglutinin combined with the bacteria in the ab- 

 sence of the salts, and the resulting compound was precipitated by the 

 addition of minute amounts of electrolytes, ^'^ which alone did not 

 precipitate or agglutinate the bacteria or the serum. This indicates 

 that the agglutinins cause a change in the bacteria which brings them, 

 under the same physical laws as the inorganic colloidal suspensions, 

 which are characterized by being precipitated by the addition of traces 

 of electrolytes."'* This precipitation is undoubted!}^ due to changes 

 in solution tension and surface tension (see "Precipitation of Colloids, " 

 introductory chapter). Before the agglutinin combines with the 

 bacteria they behave like the colloidal solutions of organic colloids, 

 being precipitated only by the salts of heav}- metals, alcohol, formalin, 

 etc., or by great concentrations of neutral salts. Field and Teague-^ 

 have found that agglutinins carry positive charges while bacteria are 

 negative, and that b}' the electric current agglutinins can be separated 

 from bacteria with which they have combined; this shows that the 

 agglutinin is not destroyed in the reaction. Teague and Buxton^^ 

 consider that neutralization of the electric charge of the bacteria is not, 

 however, the only important factor in agglutination. 



According to Bechhold^^ normal bacteria behave like inorganic 

 suspensions that have each particle protected by an albumin-like 

 membrane, which prevents them from being thrown out of suspension 

 by solutions of alkali salts, etc. After being acted on by agglutinin 

 they are so altered that they behave like the unprotected inorganic 

 suspensions, and are precipitated by salts and other electrolytes. 

 This suggests the possibility that the agglutinin makes the bacteria 



22 Ann. d. I'Inst. Pasteur, 1899 (13), 225. 



23 Corroborated for sensitized red corpuscles by Eisner and Friedemann, Zeit. 

 Immunitat., 1914 (21), 520. 



2* Arrhenius (Zeit. physikal. Chem., 1903 (46), 415) has attempted to show 

 that the gas laws are applicable to the partition of agglutinin between the bacteria 

 and the medium, which he compares to the partition of iodin between water and 

 carbon disulphid. This idea is not accepted Vyy Craw {loc. cit.), nor by Drej'er 

 and Douglas, Proc. Roval Soc, 1910 (82), 185. 



25 Jour. Exper. Med\, 1907 (9), 86. 



2« Zeit. phvsikal. Chem., 1907 (57), 76. 



2' Zeit. f. physikal. Chem., 1904 (48), 385. 



