188 CHEMISTRY OF Till; IMMUyiTY REACTIONS 



lion. Agglutination obeys the same laws as other similar physical 

 phenomena ; the rate of agglutination depends upon the concentration 

 of the suspension and of the electrolytes, and varies with the valence 

 of the cations. Although bacteria in an electric stream move toward 

 the anode like all suspensions, after being acted on by agglutinin they 

 are agglutinated by the current between the poles ; ^^ this indicates 

 the importance of the electrical charges of the bacterial surfaces in 

 tlieir agglutination reactions. 



In all respects the behavior of bacteria and agglutinin resembles 

 the behavior of colloidal mixtures in suspension (Neisser and Friede- 

 mann) ^~ which form an electrically amphoteric colloidal suspension, 

 so that the ions of electrolytes or the electric currents, by discharging 

 them unequally, cause precipitation. Pliysico-chemical researches, 

 however, have yet failed to explain the specific character of the ag- 

 glutinins for specific bacteria, but IMiehaelis *^ has developed an inter- 

 esting analogy in the specific agglutination of bacteria by acids. This 

 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 agglutination of bacteria 

 by acids, the agglutination by acids being even more sharply specific 

 in some cases than the agglutination by immune sera ; e. g., typhoid 

 and paratyphoid bacilli are readily distinguished because the former 

 are agglutinated by a concentration of H ions from -4 to 8 X 10"'', while 

 paratyphoids require 16 to 32 X 10'^, 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 3.6 X 10"^ 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 bacilli freshly cultivated from human infections 



SI Ilcclihold: liowcver, Buxton and Teag-ue (Kolloid Zoitsolir., 1908, II, Suppl. 

 2) state that agfjlutinin bacteria do move towards tlie anode, but slower tlian 

 normal bacteria. 



82 Miincli. med. \A'ocli., 1!)04 (51), M\'-> and S'27 ; sec also (iiiard-MaiiL:iii and 

 Henri, C'ompt. Rend. Soe. IJiol., ]i)04, vol. 5fl ; and Zanggcr, Cent. f. Hakt! ( ref. ) , 

 ino.5 (.'^(i), 225. 



83 Folia Serologica, 1911 (7). 1010; also Benias.li, Zeil. InninuiitiU., 1!U2 (12), 

 268. 



83a See Kemper, .Tour. Tnf. Di.s., ]!)1G (18), 200. 



831. Z,Mt. Imnuniitiit., 1014 (22), .SOO; Jour. Ilyg., 1014 (H). -'(W. 



84 Krumwiede and Pratt, Zeit. Immunitiit., 1013 (10). 7^\'i . 



