232 Chapter VIII 



in the suppression of the acquired immunity of the guinea-pigs. 

 These experiments supply a fresh proof of the great importance of 

 the phagocytic reaction in this kind of immunity, and afford further 

 confirmation of the analogy between the mechanism of resistance of 

 the animal's organism against the typhoid bacillus and that against 

 the cholera vibrio. 



In presence of this striking analogy, it is unnecessary to insist 

 further on the details of the acquired immunity of animals against 

 the experimental disease set up by the micro-organism of typhoid 

 fever. It will be better to select another example from the group 

 of bacilli. Let us first take the acquired immunity against the 

 bacillus of blue pus {Bacillus pyocyaneus) which for many years has 

 been regarded as the best example in which to study this kind of 

 immunity. Charrin, who was the first to obtain disease with this 

 bacillus experimentally, published several notes ^ on the acquired 

 immunity of the rabbit against it. He demonstrated the possibility 

 of vaccinating this animal not only with living bacilli, but also with 

 the products of their culture; he studied the blood serum of vacci- 

 nated animals, comparing it with the serum of normal rabbits, 

 especially as to its action on the development of the Bacillus pyo- 

 cyaneus. Although unable to find any bactericidal power properly 

 so called in the serum of immunised rabbits, Charrin was the first 

 to draw attention to certain modifications undergone by the bacilli 

 when grown in this medium. He noted that under these conditions 

 no pyocyanin was produced, and, in collaboration with Roger, he 

 demonstrated that, in the serum of the vaccinated rabbit, the Bacillus 

 pyocyaneus forms packets composed of little chains of greater or 

 less length, whilst in the serum of the normal, susceptible rabbit, 

 it develops in the form of normal rods, the rods for the most part 

 being isolated. 



From his experiments in vitro Charrin concluded that there was 

 marked enfeeblement of the functions of the Bacillus pyocyaneus 

 when submitted to the action of the vaccinated animal organism. 

 [245] Bouchard^ has gone so far as to develop a theory of acquired 

 immunity, in which the principal part is attributed to the impos- 

 sibility of the micro-organism, after it has invaded the refractory 

 animal, secreting its fluid products; there is no vascular dilatation 

 and diapedesis does not take place. A comparative observation of the 



1 Compt. rend. Soc. de biol., Paris, 1889, pp. 250, 330, 627 ; 1890, pp. 203, 332, 195. 



2 "Les microbes pathogenes," Paris, 1892. 



