278 THE BACTERIOPHAGE 



and only stops, or assumes a sporadic character, when there has 

 been a diffusion of a bacteriophage virulent for the pathogenic 

 bacterium. 



The bacteriophagous ultramicrobe virulent for a given bac- 

 terium is cultivable in vitro. It is therefore possible to obtain 

 it in any desired amount. If its protective power is real a sus- 

 ceptible individual should be rendered immune by inoculation, 

 just as though he had naturally resisted the contagion. This 

 has been demonstrated to be the case in the experiments made 

 on avian typhosis and in hemorrhagic septicemia in the buffalo. 



The injection of an individual with a culture of the bacterio- 

 phage virulent for a given bacterium is harmless and causes no 

 reaction, even when the bacteriophage has developed at the ex- 

 pense of a highly toxic bacterium — B. dysenteriae or B. pestis, 

 for example. The injected ultramicrobes pass quickly into 

 the intestine. 



The injection of a culture of the bacteriophage provokes two 

 types of immunity, heterologous and homologous. 



The heterologous antimicrobial immunity is effective immediately. 

 Indeed, it exists simply by virtue of the presence in the body of a 

 bacteriophage active for the causative bacterium. In an un- 

 contaminated or non-epidemic area this immunity is transitory. 

 In a contaminated or epidemic area it persists as long as rein- 

 fections occur. 



The homologous, or organic immunity, develops after an incu- 

 bation period. It results from the production of specific anti- 

 bodies, most likely substances similar to the antitoxins. These 

 antibodies are detectable in the serum of the immunized animal 

 and persist there for a period at present undetermined (more 

 than seven months in the case of avian typhosis). The period 

 of incubation in the homologous immunity is the longer as the 

 dose injected is greater. 



The immunization experiments against barbone have shown 

 us the importance of the question of dosage. The quantity of 

 bacteriophage culture necessary and sufficient to provoke or- 

 ganic immunity ought, in all cases, to be injected at a single time. 

 As to the dose itself, it must certainly vary in accordance with 

 the disease under consideration, and, consequently, with the 





