BACTERICIDAL PROPERTIES OF BLOOD SERUM 137 



have obtained information which has made possible a correlation 

 between these two main paths of thought. 



The humoral theory was conceived by Buchner, as the first 

 important theoretical result of Nuttall's discovery. Buchner, as 

 we have seen, confirmed the observations of Nuttall both as 

 to the primary fact of the bactericidal power of the fresh normal 

 blood and as to the unstable nature of this bactericidal property. 

 He looked upon the antibacterial power as depending upon a con- 

 stituent of the fresh blood plasma, which he named "alexin" (pro- 

 tective substance), and which he believed to be comparable to a 

 proteolytic enzyme. The action of this alexin was conceived as 

 potent against all bacteria equally, without showing specific selection 

 of various species to any great extent. The analogy to ferment 

 action was formulated by Buchner because of the heat sensitiveness 

 and the instability of the bactericidal substance on standing ; and he 

 suggested that this alexin might possibly be a product of the tissue or 

 blood cells, possibly leukocytic in origin. 



Buchner found that the action of the ferment-like alexin upon 

 bacteria was most marked at the temperature of the body, and that 

 it was capable of destroying bacteria in the subcutaneous tissues and 

 the serous cavities of the animal body, without the aid or coopera- 

 tion of cellular elements. He inferred that there was a direct rela- 

 tion between the potency of the alexin and resistance against infec- 

 tion. 



The next great step in the understanding of the bactericidal 

 processes was now made by Pfeiffer as a consequence of studies upon 

 the nature of cholera immunity. Pfeiffer 11 12 found that the injec- 

 tion of cholera spirilla into the peritoneal cavity of a guinea pig 

 which had recovered from a previous cholera infection was fol- 

 lowed by a rapid destruction of the bacteria. If small quantities of 

 exudate were taken out of the peritoneum at varying intervals after 

 the injection, a granular change and swelling of the bacteria were 

 noticed, followed, soon after, by complete dissolution and disappear- 

 ance. Such animals would recover from doses of bacteria which, in 

 control animals of the same weight, resulted in death. He further 

 found that the phenomenon was specific, in that the dissolution of 

 cholera organisms only occurred in the cholera-immune animals, 

 other bacteria being unaffected. In other words, the guinea pig had 

 acquired a specific antibacterial power, expressed by the process of 

 "bacteriolysis," a property possessed to only a very slight extent by 

 the peritoneal exudate of a normal animal. It was the next logical 

 step to determine whether the bacteriolytic power could be trans- 

 ferred to the peritoneal cavity of a normal animal by injecting, to- 

 gether with the bacteria, a small amount of the serum of such an 



"Pfeiffer. Zeitschr. f. Hyg., Vol. 18, 1894; also Vols. 19 and 20. 

 12 Pfeiffer & Isaeff. Deutsche med. Woch., No. 18, 1894. 



