Acquired immunity against micro-organisms 281 



tended to other micro-organisms. Massart 1 studied the general 

 subject and collected a series of data which led him to say that 

 " vaccination effects an education of the leucocytes ; these latter 

 become so adapted that they can approach the virulent micro- 

 organisms.'' The best method of forming an estimate of the change 

 which the leucocytes undergo is by injecting subcutaneously very [295] 

 virulent micro-organisms capable of setting up a generalised in- 

 fection. The anthrax bacillus, Gamaleia's vibrio, the streptococci and 

 the cocco- bacilli of swine and fowl cholera are very suitable for such 

 study. These micro-organisms, when inoculated subcutaneously into 

 susceptible animals, set up a very slight local reaction or none at all, 

 in the form of an exudation of transparent fluid almost entirely 

 without leucocytes. The micro-organisms grow freely in these ex- 

 udations and soon invade the animal. In vaccinated animals the 

 local reaction is more marked and the exudation, very rich in 

 leucocytes, is poor in fluid ; the micro-organisms remain free for a 

 very short time, being soon ingested by the leucocytes. Their de- 

 struction, inside these cells, takes a longer or shorter time according 

 to circumstances ; but in the end it is always complete. 



The difference as regards phagocytic reaction between susceptible 

 and vaccinated animals, such as I have just described, has been 

 generally recognised by many observers. A few opponents are still 

 found, however, who consider that they are justified in affirming that 

 the negative chernio taxis of the susceptible animal does not exist and 

 that, consequently, vaccination can in no way change it into positive 

 chemiotaxis. Werigo made himself the spokesman of this view, 

 which he has maintained in several papers 2 . Instead, however, of 

 introducing the virulent micro-organisms into the subcutaneous 

 tissue of susceptible animals he injected them directly into the veins. 

 Using cultures of the anthrax bacillus and of the cocco-bacillus of 

 fowl cholera he injects these into the venous system of normal 

 rabbits. The animals soon die from general infection. If, however, 

 these animals are killed shortly after inoculation, it is found on 

 examination of sections that many of the micro-organisms have 

 been ingested by the leucocytes. Werigo concludes from these facts 

 that in the higher animals the chemiotaxis is always positive ; but 

 that it ends in the destruction of the micro-organisms in the vaccin- 



1 Ann. de Vlnst. Pasteur, Paris, 1892, t. vi, p. 321. 



2 Ann. de VInst. Pasteur, Paris, 1894, t. vm, p. 1 ; Arch, de med. exper., Paris, 

 1898, t. x, p. 725; Arch, russes de Path. &c., St Petersb., 1898. 



