Immunity against micro-organisms 301 



that the immunity conferred by micro-organisms or their products 

 requires some time for its development and endures for a long period, [316] 

 whilst the immunity due to the introduction of specific serums into an 

 animal is set up immediately, but endures for a very short time only. 



The diseases of the Invertebrata being seldom due to the micro- 

 organisms that produce infections in the higher animals, the question 

 as to whether the Invertebrata can be immunised by means of pro- 

 tective serums has not yet been studied. Still, we already have certain 

 ideas on the protection of lower vertebrates by specific serums. 

 Gheorghiewsky 1 , in my laboratory, carried out some experiments on 

 this point. He found that the serum of mammals (guinea-pig, goat) 

 immunised against the Bacillus pyocyaneus, was under certain con- 

 ditions capable of protecting the green frog against a dose of this 

 organism that was always fatal to the control animals. When 

 injected along with the Bacillus pyocyaneus, the serum did not 

 prevent a fatal infection ; sometimes this infection developed even 

 more rapidly than in the control frogs. It was only when the pro- 

 tective injection was made 24 or, better still, 48 hours before the 

 inoculation of the bacilli, that the protective action became evident. 

 The serum used in these experiments was not bactericidal for the 

 Bacillus pyocyaneus which grew most luxuriantly ; but it agglutinated 

 a large proportion of the bacilli. Gheorghiewsky pointed out, how- 

 ever, that frogs injected with cultures agglutinated by the goat's serum 

 died just as readily as did the control animals. As the phagocytic 

 reaction was invariably very active in those frogs which resisted the 

 virus, after the injection of protective serum, it is very probable that 

 this fluid exercises a stimulant influence on the phagocytes. 



This idea of stimulation by anti-infective serums in cases of tem- 

 porary immunity conferred by these fluids, has already been set forth 

 in my researches on the immunity of rabbits against the Gentilly 

 cocco-bacillus, induced by the serum of vaccinated rabbits. This 

 view, however, has not been favourably received, especially in view 

 of the discovery of the phenomenon of the transformation of cholera 

 vibrios into granules. Pfeifler himself noted that this transformation 

 took place not only in the peritoneal cavity of vaccinated guinea-pigs 

 but also in the peritoneal cavity of normal guinea-pigs, into which he [317] 

 had injected small quantities of specific serum. As this latter fluid, 

 in Pfeiffer's hands, was incapable of transforming the vibrios into 

 granules in vitro, he concluded that the cellular elements of the 

 1 Ann. de VInst. Pasteur, Paris, 1899, t. xin, p. 315. 



