238 Chapter VIII 



The researches on immunity against swine erysipelas then lan- 

 guished for some time, until the discovery of Pfeiffer's phenomenon 

 gave a fresh stimulus to the study of this problem. One of Pfeiffer's 

 pupils, Voges 1 , sought to apply the results obtained in the case of 

 the cholera vibrio to the acquired immunity against the bacillus 

 of swine erysipelas. He studied the blood serum of animals vacci- 

 nated against this bacillus and believed himself justified in affirming 

 the existence of an acquired bactericidal power. Under no con- 

 dition, however, did he observe anything comparable to Pfeiffer's 

 phenomenon, and he was compelled to admit that the bactericidal 

 action of the serum is very feeble and only takes effect on young 

 bacilli whose membranes are as yet very delicate and not very 

 resistant. Mesnil 2 repeated these researches in my laboratory, but 

 his results were very different from those obtained by Voges. The 

 blood serum of rabbits, fully vaccinated against the bacillus of swine 

 erysipelas, proved to be a good culture medium for this bacillus, and 

 Mesnil affirms, as the result of numerous well-established obser- 

 vations, that "in vitro, the serum of rabbits immunised against the 

 erysipelas has no bactericidal power or a very insignificant one." On 

 the other hand, the same fluid had a very marked agglutinative 

 power. The bacillus of swine erysipelas, being non-motile, does not 

 present the abrupt change that is observed in vibrios or in the 

 typhoid bacillus when submitted to the influence of specific serums 

 under which conditions these organisms at once lose their motility. 

 But the bacilli of swine erysipelas, when introduced into the specific 

 serum of vaccinated animals, run together into masses which become 

 [251] more and more voluminous and fall to the bottom of the vessel, 

 leaving a limpid supernatant fluid. When this bacillus is sown in 

 the serum of vaccinated animals, it is seen to develop in the form 

 of chains, composed of a large number of segments, which fall to 

 the bottom of the tube. These bacilli, however, whether agglutinated 

 or developed in chains, never show any attenuation in virulence. 

 When the serum which bathes them is got rid of by washing, they 

 are just as virulent as are the bacilli developed in the serum of 

 normal unvaccinated rabbits. It is important to show that this 

 virulence is kept up in spite of the fact that the bacilli, when placed 

 in contact with the serum of immunised animals, become permeated 



1 Ztschr.f. Hyg., Leipzig, 1896, Bd. xxn, S. 515; Deutsche med. Wchnschr., 

 Leipzig, 1898, S. 49 ; Ztschr.f. Hyg., Leipzig, 1898, Bd. xxvm, S. 38. 



2 Ann. de I'Inst. Pasteur, Paris, 1898, t. xu, p. 481. 



