148 THE BACTERIOPHAGE 



second hypothesis, that is, to a substance derived from the bac- 

 terium itself. 



This hypothesis fails before the following experimental facts: 



a. The bacteriophage exists in the form of particles which 

 multiply. 



b. The bacteriophage does not exercise a specific action upon 

 any single species of bacteria, but at one and the same time, the 

 same bacteriophage may be active against several species. 



c. All strains of the bacteriophage, whether they be active 

 against the staphylococcus, against the dysentery bacillus, against 

 B. pestis, or against any other organism, belong to the same species, 

 as demonstrated by the complement fixation reaction. 



2. The bacteriophage is derived from the bacterium, but is 

 particulate, an "organite" capable of life, conducting itself thence- 

 forth like an autonomous ultramicrobe. This is the hypothesis 

 of Bail. 



While an interpretation which comprehends an " organite" 

 derived from the superior parasitized organism does not neces- 

 sarily imply specificity of the bacteriophage, any hypothesis in- 

 volving an " organite" derived from the bacterium which is sub- 

 jected to lysis does imply a strict specificity. The last view, 

 therefore, is inadmissible, since experiment proves that a single 

 strain of the bacteriophage may be active toward several species 

 of bacteria at once, and that all strains of the bacteriophage be- 

 long to the same species. 



All possible hypotheses, save that of the ultramicrobe, which 

 we will shortly examine, can only be some combination of the 

 two preceding ones. All, then, will be subject to the same ob- 

 jections; none will be admissible for it will be contradicted by 

 experimental facts. 



Third hypothesis 



The bacteriophage is an autonomous organism, an ultramicrobe 

 parasitizing the bacteria. This hypothesis is the only one which 

 accords with all the recorded experimental facts, and it is for 

 this logical reason that I have attached myself to it. For it, I 

 have acquired more and more convincing evidence which I have 

 not been able to disprove, for the numerous new facts that I 



