Facts bearing on acquired immunity 239 



with the specific fixative, as shown by the experiments of Bordet 

 and Gengou 1 . These observers, indeed, have demonstrated that the 

 bacilli of swine erysipelas, when kept for 24 hours in the specific 

 serum heated to 55 C., acquire the property of absorbing the cytases 

 contained in the unheated serum of normal animals. 



The study of acquired immunity against the bacillus of swine 

 erysipelas teaches us that this immunity is not due to any extra- 

 cellular destruction comparable with Pfeiffer's phenomenon ; and that 

 this immunity causes the production of a specific fixative and of a 

 specific agglutinative substance, whose action on the resistance of the 

 animal, to judge from the complete virulence of the bacilli when 

 agglutinated and impregnated by fixative, is feeble or nil. It is 

 the phagocytic reaction which is dominant in the immunised animals 

 and which brings about the intracellular destruction of the bacilli. 



The history of the anthrax bacillus, another representative of the 

 group of non-motile bacilli, is particularly interesting, the more so 

 that for some time the researches on acquired immunity have been 

 concentrated almost entirely on the analysis of the facts observed 

 in animals that have been vaccinated with the two Pasteur vaccines. 

 In this way a large number of valuable facts have been collected; 

 of these the more important may be presented to the reader. 



In my first work on this subject 2 I called attention to the fact 

 that in the rabbit vaccinated against anthrax, the bacilli, when 

 inoculated subcutaneously, soon become the prey of leucocytes which 

 accumulate at the spot menaced. In the unvaccinated control 

 rabbits, however, the anthrax bacilli remain in a free state in the 

 fluid of the subcutaneous exudation, only a few isolated rods being [252] 

 found inside phagocytes. I have since been able to confirm this 

 fact 8 , which must now be regarded as fully established. In the 

 vaccinated rabbits the leucocytes exhibit a very marked positive 

 chemiotaxis against the anthrax bacilli, whilst in normal unvacci- 

 nated rabbits the chemiotaxis of the leucocytes in the anthrax of 

 the subcutaneous tissue is distinctly negative. When a small quantity 

 of anthrax culture is inoculated subcutaneously into vaccinated and 

 into unvaccinated rabbits there may be observed, even within a few 

 hours, a very great difference. In the former there is found at the 

 seat of inoculation an infiltration which swarms with leucocytes 



1 Ann. de Flnst. Pasteur, Paris, 1901, t. xv, p. 295. 



2 Vir chow's Archiv, Berlin, 1884, Bd. xcvii, S. 502. 



3 Virchow's Arc/iw, Berlin, 1888, Bd. cxiv, S. 465. 



