534 IMMUNITY 



these the two first are concerned with the protective property of 

 an anti-bacterial serum. 



(a) Bactericidal and Lysogenic Action. Pfeiffer found that 

 if certain organisims, e.g. the cholera spirillum, were injected 

 into the peritoneal cavity of a guinea-pig highly immunised 

 against these organisms, they lost their motility almost immedi- 

 ately, gradually became granular, swollen, and then disappeared 

 in the fluid these changes constitute "Pfeiffer's phenomenon." 

 Further, he showed that the same phenomenon was witnessed if 

 a minute quantity of the anti-serum was added to a certain 

 quantity of the corresponding organisms, and the mixture injected 

 into the peritoneal cavity of a non-treated animal. Pfeiffer 

 found that the serum of convalescent cholera patients gave the 

 same reaction as that of immunised animals. He obtained the 

 same reaction also in the case of the typhoid bacillus and other 

 organisms. From his observations he concluded that the reaction 

 was specific, and could be used as a means of distinguishing 

 organisms which resemble one another. He accordingly con- 

 sidered that a specific substance was developed in the process of 

 immunisation, and that this was rendered actively bactericidal 

 by the aid of the living cells of the body. It was subsequently 

 shown, however, by Metchnikoff and by Bordet that lysogenesis 

 might occur outside the body by the addition of fresh peritoneal 

 fluid or normal serum to the heated immune-serum. PfeifFer 

 also found that an anti-serum heated to 70 C. for an hour pro- 

 duced the reaction when injected with the corresponding organisms 

 into the peritoneum of a fresh animal. The outcome of these 

 and subsequent researches is to show that when an animal is 

 immunised against a bacterium a substance appears in its serum 

 with combining affinity for that particular organism. This 

 substance, which is generally known as the immune-body, 

 amboceptor (Ehrlich), or substance sensibilisatrice (Bordet) is 

 comparatively stable, resisting usually a temperature of 70 C. 

 for an hour. It cannot produce the destructive effect alone, but 

 requires the addition of a substance normally present in the serum, 

 which is spoken of under various names complement (Ehrlich), 

 alexine or cytase (French writers). The complement is relatively 

 unstable, being rapidly destroyed by a temperature of 60 C., 

 and it is not increased in amount during the process of 

 immunisation. Though ferment-like in its instability, it differs 

 from a ferment in being fixed or used up in definite quantities. 



Eecent observations show that complement is not a single substance, 

 but is really made up of two components. Ferrata, who was the first to 

 establish this fact, employed the following method : Fresh guinea-pig's 



