260 THE BACTEEIOPHAGE 



Examination of the opsonic power of two of these sera gave 

 indices of 0.3 and 0.4; indices which are essentially negative. 6 



The serum containing the protective principle does not con- 

 tain inhibiting substances or even substances delaying the growth 

 of the bacterium of barbone. Bouillon, mixed with such a serum, 

 in any proportion (from 0.05 cc. to 3 cc. per 10 cc. of bouillon), 

 with or without the addition of fresh guinea pig serum, furnishes 

 a medium which, when inoculated, gives luxuriant cultures of the 

 bacterium of barbone. 



Finally, the serum contains no traces of agglutinins. 



Organic immunity, then, is not due to the presence of an am- 

 boceptor, nor to the presence of an opsonin in the blood of the 

 vaccinated subjects. The blood contains neither agglutinins 

 nor inhibiting substances. The immunity is most probably 

 antitoxic. 



We have seen in the experiments performed on avian typhosis, 

 that, in an infected area, the protection of the animal is immediate 

 and that this protection is assured only by the presence of bac- 

 teriophagous ultramicrobes virulent for the pathogenic bac- 

 terium. We have again found this immediate immunity in the 

 case of barbone. It is that which protected steers nos. 103 and 

 107 against the inoculation of five fatal doses of culture when 

 given only twenty-four hours after the injection of the 

 bacteriophage. 



In typhosis, this heterologous immunity has been permanent, 

 for the daily reinfections which occur in the infected area allow 

 the bacteriophage to multiply at the expense of the pathogenic 

 bacteria ingested and thus to maintain its virulence for this 

 bacterium. In barbone, this same thing takes place in an in- 

 fected area, since we have seen that the bacteriophage virulent 

 for the bacterium of barbone was present in the intestine of 

 buffaloes five months after the complete disappearance of the 

 epizootic. 



6 We have seen in Part I that the lysin secreted by the bacteriophage 

 possesses a very high opsonic power. The organism must respond to an 

 injection of lysin (certainly present in the culture of the bacteriophage) 

 by the production of an anti-opsonic antibody. 



