302 Chapter X 



normal animal were endowed with the power of modifying the in- 

 active substance of the specific serum into bactericidal substance. 

 According to this conception the immunity conferred by this serum 

 was not entirely passive since, in order to prepare the substance 

 which transforms and kills the vibrios, the co-operation of the living 

 cells was necessary. 



My demonstration of the possibility of obtaining Pfeiffer's pheno- 

 menon in vitro at once turned the balance in favour of the theory 

 that the immunity induced by the specific serum is due to a direct 

 humoral action upon the micro-organism. Under these conditions 

 such immunity could only be interpreted as being purely passive. 

 This view seemed to be finally established by Bordet's discovery that 

 a specific serum, inactive by itself, became capable of producing 

 Pfeiffer's phenomenon, as soon as a small quantity of normal, non- 

 specific serum was added to it. Bordet 1 thus sums up his theory of 

 the immunity conferred by specific serums : " Passive immunity is 

 due, in part at least, to a chemical action exerted on the vibrios by 

 two pre-formed substances, the one present in the animal before any 

 injection is made, the other found in the serum that is injected; this 

 phenomenon is purely chemical in the sense that it can go on without 

 the aid of a vital reaction, of any new cell secretion : indeed it is 

 found to take place in fluids from which the cells have been entirely 

 removed" (p. 217). These demonstrations led up to the belief that 

 the organism of the animal remained absolutely passive when it was 

 subjected to the action of protective or anti-infective serums, and that 

 the case of the cholera vibrio represented a kind of schema, which 

 was applicable to the whole of the group of phenomena met with in 

 passive immunity. 



As in the study of the immunity obtained as the result of vaccina- 

 tions with micro-organisms or their products, so in "passive immunity" 

 there was seen only the direct chemical action of two substances on 

 the micro-organism, and efforts were made to extend this demonstration 

 to a series of infective diseases. 



[318] Pfeiffer and Kolle 2 having observed that the blood serum of 

 persons convalescent from typhoid fever, as well as that of animals 

 vaccinated with the typhoid bacillus, exhibited a great protective 

 power for the guinea-pig, wished to get some idea of the mechanism 

 of this immunity. They found that in the peritoneal cavity of guinea- 



1 Ann. de VInst. Pasteur, Paris, 1896, t. x, p. 193. 

 58 Ztschr. f. Hyg., Leipzig, 1896, Bd. xxi, S. 203. 



