UNICITY OF BACTERIOPHAGE PROTOBE 6bd 



I have performed with three different strains of B. typhosus the fol- 

 lowing experiment. By suitable contacts a strain of the typhoid bacillus 

 is induced to acquire a resistance to a race of the bacteriophage which, 

 at the same time was virulent for B. typhosus, B. coli, and B. dysenteriae. 

 But, and this is the significant point, when tested later, this B. typhosus, 

 although resistant to the bacteriophage developed through passages 

 with B. typhosus, is bacteriophaged perfectly by the same race which 

 in the meantime has undergone passages with either B. coli or with B. 

 dysenteriae. 



If we may find an inequality in the resistance acquired by one bac- 

 terium for a single bacteriophage developed at the expense of different 

 bacteria, there is the more reason that it may be observed with different 

 races. Certainly it can not weigh very heavily against the idea of the 

 unicity of species of the bacteriophage. 



As for the fourth objection, it disregards the fact, recorded by many 

 authors, that the size of the plaque* is, with a given race of the bacterio- 

 phage, strictly related to its virulence. If the diameter of the plaque 

 varies for a single race of the bacteriophage it can hardly cause astonish- 

 ment if it varies for different races for the same reason. 



The protobes, the bacteriophage in particular, hke the microbes, the 

 bacteria especially, are beings endowed with a very considerable power 

 of adaptation. The variabihty which we find in antigenic properties 

 shows further that assimilation is not brought about in the same manner 

 in rudimentary beings as in beings more highly organized. According 

 to the foodstuff utihzed, even the substance of these beings shows 

 variations. These two experimental facts demonstrate that as a con- 

 sequence there must be an extreme variability in all characters in con- 

 formity to the conditions of the moment. There is but a single species 

 of the bacteriophage, as is shown by the phenomenon of multiple virul- 

 ences and by the possibility of experimental adaptation. But within 

 this single species each race presents its own characters distinguishing 

 it from other races, characters which are, nevertheless, variable from 

 one time to another. 



5. THE MODE OF ACTION OF THE BACTERIOPHAGE 



Study of the phenomenon of bacteriophagy shows us that, most prob- 

 ably because of some chemotactic force, a bacteriophage protobe is 



* Bruynoghe says "the form" of the colony. This term is incorrect, for plaques 

 are always perfectly circular; only the diameter may vary. 



