232 INFECTION AND IMMUNITY 



in their development, and that strongly agglutinating sera may be ex- 

 tremely weak in bactericidal substances and vice versa, the relative quan- 

 tity of either of these substances depending to a certain extent upon 

 the method of immunization. Whether or not agglutinins possess 

 any direct protective function can not at present be stated with certainty. 

 Metchnikoff ^ assigns to them a purely secondary r61e. As a matter of 

 fact, agglutinated bacteria ^ are not killed by the act of agglutination 

 and are often as virulent as non-agglutinated cultures. 



The agglutinins, furthermore, unlike the bactericidal substances in 

 sera, remain active after exposure to temperatures of over 55° C, some 

 of them withstanding even 65° to 70°, and can not be reactivated by the 

 subsequent addition of normal serum. These facts definitely preclude 

 the participation in the reaction of the alexin or complement and have 

 an important bearing upon Ehrlich's views of their structure ' (see 

 page 238). 



As a result of these and a multitude of other studies, the agglu- 

 tinins have come to be regarded as separate antibodies, closely related 

 to the precipitins. 



The agglutinins may be chemically precipitated out of serum together 

 with the globulins. They do not dialyze. Bordet * made the observa- 

 tion that agglutinins do not act in the absence of NaCl. Whether the 

 presence of the salt aids the reaction in a chemical or purely physical 

 way, as Bordet supposed, is uncertain. 



Production of Agglutinins. — ^Just as normal sera contain small quan- 

 tities of bactericidal substances, so do they contain agglutinins in small 

 amount. In a general way these " normal agglutinins " have the same 

 nature as the immune agglutinins, and it is probable that their presence 

 is traceable to the various microorganisms parasitic upon the human and 

 animal body. 



As a matter of fact, the blood serum of new-born guinea-pigs hardly 

 ever contains agglutinin for B. coli, while that of adults acts upon these 

 bacilli in dilutions of 1 : 20.^ Similarly, infants show lower normal ag- 

 glutinating values than adults." 



1 Metchnikoff, " L'immunit^,'' etc., 1901, p. 214. 



2 Mesnil, Ann. de I'inst. Pasteur, 1898. 



s Pane, Cent. f. Bakt., 1897; Trumpp, Arch. f. Hyg., 1898; Forster, Zeit. f. Hyg., 

 xxiv. 



< Bordet, Ann. de I'inst. Pasteur, 1899. 



'' Kraus und Low, Gesell. d. Aerzte, Wien, 1899. 



« Pfaundler, Jahrb. f. Kinderheilk., Bd. 50. 



