CHAPTER XV 



SENSITIZING ANTIBODIES. ' (PHENOMENA OF LYSIS, AGGLUTINA- 

 TION, PRECIPITATION, E^C.) 



Alexin and Sensitizing Antibodies. In the immediately preced- 

 ing sections, we have dealt solely with immunity as it occurs where 

 soluble toxins play an important part and in which antitoxins are 

 developed in the immunized subject. There are many species of 

 pathogenic bacteria, however, which stimulate the production of 

 little or no antitoxic substance when introduced into animals, and 

 the resistance of the immunized animal can not, therefore, be ex- 

 plained by the presence of antitoxin in the blood. 



v. Fodor, 1 Nuttall, 2 Buchner, 3 and others had in 1886 and the 

 years following, carried on investigations which showed that normal 

 blood serum possessed the power of killing certain of the pathogenic 

 bacteria. Nuttall, working under the direction of Fliigge, made 

 the important discovery that this bactericidal power became grad- 

 ually diminished with time, and could be experimentally destroyed 

 by exposure of the serum to a temperature of 56 C. for one-half 

 hour. Buchner, who confirmed and extended the observations of 

 Nuttall, called this thermolabile substance upon which the bacteri- 

 cidal character of the serum seemed to depend "alexin. " 



Our knowledge of the bactericidal action of serum was, soon 

 thereafter, extensively increased by the discovery, by Pfeiffer and 

 Isaeff, 4 that cholera spirilla injected into the peritoneal cavity of 

 a cholera-immune guinea-pig were promptly killed and almost com- 

 pletely dissolved. The same phenomenon could be observed when 

 the spirilla, mixed with fresh immune serum, were injected into the 

 peritoneum of a normal guinea-pig. 



The processes observed by Pfeiffer as taking place intraperi- 



*. Fodor, Dent. mod. Woch., 1886. 



2 Nuttall, Zeit. f. Hyg., 1886. 



1 Buchner, Cent. f. Kakt., 1SS9. 



4 Pfeiffer und Isaeff, Zeit, f. Hyg., 1894. 



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