INTRODUCTION 169 



individuals exposed to an infection do not contract the disease, 

 and to what do they owe this privilege? Once diseased, the 

 immunity in the susceptible animal manifests itself only after a 

 lapse of time, which in the most favorable cases is hardly less 

 than twelve days. 4 Does the animal remain without defense 

 during this lapse of time? Finally, in this animal affected by 

 disease, whatever may be the mechanism of organic immunity, 

 how can this immunity be established to render this sick animal 

 refractory? Under what influence is phagocytosis released? 

 Under what influence do the antitoxins originate? 



The role which the partisans of the theory of "bactericidal 

 humoral immunity' ' have desired that these simple indices of 

 infection — the antibodies — play, is based upon a non-existent 

 phenomenon of bacteriolysis by immune sera. Could it not in 

 reality be played by the bacteriophage, that principle endowed 

 with a powerful bacteriolytic action, operating upon the most 

 varied bacteria? 



Could not the bacteriophage play a role in the defense of the 

 organism, a preponderant role in the susceptible animal, and as 

 such, deprived of all acquired immunity? In other words, does 

 there not exist by the side of the homogeneous organic immunity, 

 an immunity originating in the bacteriophagous ultramicrobe, 

 and, as a result, an heterogeneous immunity? 



We have seen in a preceding chapter that the lysin of the bac- 

 teriophage may possess an extraordinarily potent opsonic activity. 

 Can not the bacteriophage play, in addition to its direct action, 

 an important role in phagocytosis itself, in bringing about what 

 might be called a phagocytic education? 



4 Animals vaccinated by an attenuated anthrax or rouget virus are not 

 protected against natural infection until after this period of time. I have 

 also shown that at least twelve to fifteen days are necessary to secure an 

 immunity following the use of an attenuated virus in bovine homorrhagic 

 septicemia. In typhoid fever, the immunity acquired as a result of infec- 

 tion is even longer in establishing itself, as the possibility of relapse in 

 well-advanced convalescence shows. This lapse of time, twelve days, 

 is therefore a minimum insofar as naturally acquired organic immunity 

 is concerned. There is nothing to be gained here by discussing laboratory 

 experiments concerning the development of immunity in refractory ani- 

 mals, for such experiments are laboratory phenomena only and have nothing 

 necessarily in common with natural conditions. 



