UNICITY OF BACTERIOPHAGE PROTOBE 377 



ity among different representatives of a species. Each race of the 

 bacteriophage presents special characters subject to variation from time 

 to time. 



The facts of multiple virulence and of an experimental adaptation 

 to the parasitism of a species previously unattacked, show that all 

 races of the bacteriophage belong to a single species, the special char- 

 acters of each race being acquired by adaptation. 



None of the arguments adduced by the partisans of the idea of a 

 plurality of species of the bacteriophage are valid, for the facts upon 

 which these arguments are based are observed just as clearly within 

 a single race of the bacteriophage as among different races. 



Only three hypotheses are possible as to the mode of action of the 

 bacteriophage protobe : 



It may act as an enzyme of which each granule is living; 



It may act by causing the bacterium itself to elaborate autolytic 

 enzymes; 



It may itself elaborate bacteriolytic enzymes. 



Upon the basis of our present knowledge it is impossible to choose 

 from among these three hypotheses. 



The fact that there is such a being as Protobios bacteriophagus permits 

 us to approach, in a scientific way, the problem of the origin of Hfe. 



