Facts bearing on acquired immunity 243 



most recent publications, expresses the opinion that this example 

 of acquired immunity must be placed in the category of phagocytic 

 immunity. 



In the group of bacilli, several examples of which we have 

 studied, the typhoid bacillus approaches still more closely to the 

 vibrios and spirilla in its relation to humoral properties. Here 

 may be observed a kind of attenuated Pfeiffer's phenomenon and 

 somewhat profound modifications taking place under the influence 

 of the serum of vaccinated animals. The Bacillus pyocyanem is 

 more resistant to the injurious influence of fluids taken from im- 

 munised animals. This resistance is still more marked in the bacillus 

 of swine erysipelas and again still greater in the anthrax bacillus. 

 Whilst, however, these properties of the fluids of the body are found 

 to be very variable and of unequal power, the phagocytic reaction 

 is constantly manifested and always very actively. The leucocytes 

 which, in susceptible animals, exhibit a very marked negative chemio- 

 taxis or only a tardy and incomplete positive chemiotaxis, have, 

 in the vaccinated animal, this positive susceptibility developed in 

 a very high degree. 



Before quitting the group of bacteria we must cast a glance at 

 the mechanism of acquired immunity against representatives of the [256] 

 group of spherical micro-organisms. Amongst the cocci the strepto- 

 cocci have been especially studied as regards this immunity. For 

 long great difficulties were encountered in vaccinating animals 

 against these chain cocci, but Roger 1 , Marmorek 2 , Denys and Leclef 3 

 overcame these obstacles and succeeded in immunising the rabbit, 

 one of the most susceptible species, to their pathogenic action. 

 More recently the larger mammals, notably the horse, have been 

 successfully immunised. A certain number of important facts, the 

 knowledge of which is useful to complete the survey of the pheno- 

 mena of acquired immunity, have thus been collected. 



Roger set himself to study the properties of the blood serum 

 of rabbits vaccinated against the streptococcus, and established 

 the fact that this fluid had not the slightest appreciable bacteri- 

 cidal action ; the streptococcus grew in it just as well as in the serum 



1 Compt. rend. Sec. de UoL, Paris, 1891, p. 538 ; 1895, pp. 124, 224; Rev. do med., 

 Paris, 1892. 



2 Ann. de VInst. Pasteur, Paris, 1895, t. ix, p. 593. 



3 La Cellule, Lierre et Louvaiu, 1895, t. xi, p. 175 ; Dull, Acad.roy. de med. de 

 ficlff., Bruxelles, 1895, No. 11. 



1(5 2 



