232 INFECTION AND IMMUNITY 



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

 tremely weak in bactericidal substances and vice versa. We ourselves 

 are not at all sure that this proves sufficiently that agglutinins and 

 bacteriolysins are distinct substances. Whether or not agglutinins 

 possess any direct protective function can not at present be stated 

 with certainty. Metchnikoff l assigns to them a purely secondary role.. 

 As a matter of fact, agglutinated bacteria 2 are not killed by the act 

 of agglutination and are often as virulent as non-agglutinated cultures. 

 Recent work by Bull seems to indicate that bacteria are agglutinated 

 in vivo as a sort of preliminary step to phagocytosis. 



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 3 (p. 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 to- 

 gether with the globulins. They do not dialyze. Bordet 4 made the 

 observation 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 their presence is probably trace- 

 able 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. 5 Similarly, infants show lower normal ag- 

 glutinating values than adults. 6 



1 Metchnikoff, "L'Immunite," etc., 1901, p. 214. 



2 Mesnil, Ann. de 1'inst. Pasteur, 1898. 



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

 xxiv. 4 Bordet, Ann. de 1'inst. Pasteur, 1899. 



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

 6 Pfaundler, Jahrb. f . Kinderheilk., Bd.-50. . 



