Acquired immunity against micro-organisms 261 



Sicard 1 , the agglutinative power was raised, two days before the 

 relapse, to a ratio (1 : 150) it had never attained during the first 

 attack. "The appearance of the relapse, two days after this ob- 

 servation" these authors add "renders it evident that the agglu- 

 tinating reaction is independent of the state of immunisation." 

 Analogous cases have been pointed out repeatedly by several 

 observers. 



The examples cited show, on the one hand, that the serum of 

 individuals endowed with acquired immunity may be without any 

 agglutinative property, but, on the other, that this power may be 

 highly developed in the serum of susceptible individuals. The argument 

 based on these data may be corroborated by several other series of 

 facts. Thus, Salimbeni 2 has pointed out that the cholera vibrio is not 

 agglutinated in the fluids of immunised animals. The subcutaneous 

 exudation of a horse treated with a large quantity of these vibrios 

 does not agglutinate Koch's vibrio except outside the body. When 

 this exudation is drawn off shortly after the injection of the vibrios, 

 the organisms render the fluid uniformly turbid. But a short ex- 

 posure to the air is sufficient to bring about the agglutination of 

 the vibrios in the same exudation. Guided by this observation, 

 Salinibeni carried out comparative experiments on the action of the 

 serum of vaccinated animals outside the body, in tubes deprived 

 of oxygen and in others exposed to the air. In the former agglu- 

 tination did not take place or was very incomplete, in the latter it [275] 

 soon came on. This fact accords perfectly with the observation of 

 Pfeiffer's phenomenon in the peritoneal cavity of guinea-pigs from 

 which we withdraw a fluid containing granules that have resulted 

 from perfectly isolated vibrios. In other micro-organisms a difference 

 has been noted in this respect. Thus Gheorghiewsky has seen the 

 agglutination of the Bacillus pyocyanem produced under the in- 

 fluence of the serum of vaccinated animals, even in tubes deprived 

 of oxygen. Durham has made a similar observation in the case of 

 the typhoid bacillus. When, however, Trumpp 3 wished to satisfy 

 himself as to the agglutination of the same organism in the body 

 of well-vaccinated guinea-pigs, he obtained only imperfect results. 

 He concluded from his experiments " that the formation of typhoid 

 clumps may precede the breaking down of the bacteria in the 



1 Ann. de I'Inst. Pasteur, Paris, 1897, t. XI, p. 411. 



2 Ann. de VInst. Pasteur, Paris, 1897, t. xi, p. 277. 



3 Arch.f. Hyg., Miinchen u. Leipzig, 1898, Bd. xxxni, S. 124. 



