IO2 Immunity 



to solvents of a ferment nature to which he applied the name 

 alexin, were many times repeated and confirmed. Pfeiffer 

 and Kolle* showed that the bacteriolytic quality of the 

 serum was intensified in experimental immunization, and 

 Bordetf showed that the processes of hemolysis and bacterio- 

 lysis were identical so far as the factors engaged were con- 

 cerned. "Pfeiffer's phenomenon" became susceptible of 

 easy interpretation, and many facts of immunity formerly 

 obscure were cleared up. 



EXPLANATION OF IMMUNITY. 



Before the facts now at our disposal had been gathered 

 together, and before the phenomena of immunity against 

 infection had been compared with those of intoxication, 

 PasteurJ and Klebs endeavored to explain acquired im- 

 munity by supposing that micro-organisms living in the 

 infected animal used up some substance essential to their 

 existence, and so died out, leaving the soil unfit for further 

 occupation. This hypothesis was known as the ''exhaus- 

 tion theory." Wernich|| and Chauveau** thought it more 

 probable that the micro-organisms after having lived in the 

 body left behind them some substance inimical to their 

 further existence. This hypothesis was known as the 

 "retention theory." Neither of these hypotheses can be 

 given more than a passing mention at present, as they both 

 fail to explain natural immunity or immunity against intoxi- 

 cation. 



Carl Roserff observed that the leukocytes of the bodies of 

 higher animals sometimes enclosed bacteria in their cyto- 

 plasm. Koch, Sternberg, and others confirmed the obser- 

 vation, but no attention was paid to it until Metschnikoff JJ 

 correlated it with other known facts and original observa- 

 tions, and came to the conclusion that the enclosed bacteria 

 had been eaten by the leukocytes in which they were killed 



*"Centralbl. f. Bakt.," etc., xx. 



\ " Ann. de 1'Inst. Pasteur," xii. 



J " Compte rendu de la Soc. de Biol de Paris," xci. 



"Arch. f. experimentele Path. u. Pharmak.," xm. 



|| " Virchow's Archives," Bd. LXXVIII. 



** " Compte rendu de la Soc, de Biol. de Paris," xc and xci 

 tf " Biologic niederste Organismen," Marburg, 1881 

 tt" Virchow's Archives," Bd. xcvi, p. 177; "Ann. de 1'Inst. Pas- 

 teur" t. i, p. 321, 1887. 



