Facts bearing on acquired immunity 227 



of the vibrios introduced into the serum. In the living organism, 

 the microcytase not being free, these vibrios, although influenced 

 by the fixative, resist until they have become the prey of the 

 phagocytes. In an investigation which was the subject of a commu- 

 nication to the International Congress of Hygiene in London in 

 1891 \ I demonstrated that the phagocytic reaction is produced with [239] 

 great intensity in guinea-pigs that have been vaccinated against 

 Gamaleia's vibrio. The inoculation of this organism into the sub- 

 cutaneous tissue, an inoculation which sets up a rapidly fatal infection 

 in untreated guinea-pigs, gives rise in immunised animals to the 

 formation of an abundant exudation, in which the numerous vibrios 

 soon meet with resistance from the phagocytes. These phagocytes 

 ingest the living vibrios, retaining them for some considerable time 

 in their interior, but in the long run always digesting them com- 

 pletely. During the last phase of this struggle, we sometimes find, 

 inside the leucocytes, vibrios that are transformed into spherical 

 granules. It was with these cells, filled with ingested vibrios, that 

 I was able first to carry out an experiment that has since been 

 repeated again and again, always with the same result. When from 

 a well- vaccinated guinea-pig a drop of subcutaneous exudation is 

 withdrawn, at a stage when all the vibrios have for some time 

 been ingested by the leucocytes, and transferred, in the form of 

 a hanging drop, to the incubator at 35 37 C., it is found that the 

 ingested vibrios develop inside the phagocytes which have died out- 

 side the animal. The vibrios first fill the leucocyte and, continuing 

 to multiply, cause the cell to burst when they distribute themselves 

 in the fluid of the hanging drop (figs. 40 and 41). This experiment 

 proves, in the first place, that the vibrios have been ingested alive, 

 and, secondly, that the plasma of the exudation was incapable of 

 preventing their later development. 



Having summarised the principal phenomena exhibited by vibrios 

 in an animal possessing acquired immunity, we must now enquire 

 whether the mode of destruction and disappearance taking place in 

 these vibrios is of general application. Naturally, we commence this 

 study with the spirilla, which in many respects present a great 

 analogy to the vibrios. The task is an easy one, thanks to a very 

 careful work recently published by Sawtchenko 2 , on the Spirochaete 



1 [ Trans. Seventh Internat. Congr. of Hyg. and Demogr. London, 1892, Vol. n. 

 p. 179 ;] Ann. de llnst. Pasteur, Paris, 1891, t. v, p. 465. 



2 Arch, russes de Pathol., etc., St Petersb., 1900, t. ix, p. 584; Sawtchenko et 

 Melkich, Ann. de llnst. Pasteur, Paris, 1901, t. xv, p. 503. 



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