270 Chapter IX 



of fatal infection in mice into which is simultaneously injected the 

 bacillus of the first vaccine. Consequently a fixative fluid is not 

 necessarily protective. This is in accordance with the fact that the 

 micro-organisms that have absorbed the fixative may, nevertheless, 

 retain their virulence. We have already cited the experiment of 

 Mesnil that the bacilli of swine erysipelas, mixed witli the specific 

 serum and then deprived of this fluid, produce a fatal infection in 

 mice. We have also drawn attention to the fact, demonstrated by 

 Sawtchenko, that anthrax bacilli, obtained from the exudation of 

 immunised rats, give rise to a fatal anthrax in normal guinea-pigs 

 and rats. The experiments of Bordet and Gengou proved that there 

 is absorption of the fixative substance by the bacilli of swine 

 erysipelas and of anthrax when placed in contact with the specific 

 serums of the immunised animals. In order that the protective 

 power may manifest itself adequately, therefore, besides the fixative 

 substance, some other factor capable of acting is also necessary. 

 [284] In connection with my work on immunity against the micro- 

 organism of swine pneumo-enteritis I was able to demonstrate that 

 the serum of vaccinated rabbits, incapable of preventing the multi- 

 plication of the specific cocco-bacillus, is also powerless to deprive it 

 of its virulence ; it is without the power of causing its agglutination 

 or of neutralising its toxin. In short, this serum appears to exercise 

 no direct action on the micro-organism, yet, in spite of that, it 

 prevents its pathogenic action. With these results before me, 

 I was led to assume a certain stimulating action of the serum on 

 the defensive elements of the animal organism and especially on the 

 phagocytic system. The discovery of the fixative property of serums 

 would lead us to believe that this stimulation was entirely useless, 

 and that the permeation of micro-organisms by the fixative was 

 amply sufficient to bring about their destruction and removal from 

 the animal. A living micro-organism in its normal form, endowed with 

 full virulence and provided with its fighting weapon, the toxin, but 

 at the same time permeated by the fixative substance, might behave 

 in the animal in some special way. It might excite a strong posi- 

 tive chemiotaxis of the leucocytes and be ingested and destroyed by 

 these cells with greater facility. A priori, there would be nothing 

 to object to in this view, but certain facts are opposed to it Thus, 

 in the case of micro-organisms just cited, we see bacteria, permeated 

 not only with the fixative but also with cytases, capable of producing 

 a fatal infection. We are thus compelled to accept the theory of an 



