UNICITY OF BACTERIOPHAGE PROTOBE 371 



Considering the subject from a somewhat different point of view, 

 there are many facts which show that the embryo, in animals as in 

 plants, behaves Hke a parasite, and that the very distinctive reactions 

 which it provokes may be brought about by a true parasite. As a 

 striking example of this fact it is only necessary to recall that the con- 

 siderable chemical activity mobilized by the plant at the moment of 

 the formation of the seed results from the reaction of the flower to a 

 stimulation of the embryo; but Bohn has shown that certain diptera — 

 the Cecidomyia — deposit their eggs in plants belonging to the Vicia 

 and Gallium genera, and that the presence of the egg leads to the forma- 

 tion of a false fruit, similar as to form, chemical composition and histo- 

 logical structure, to that of the true fruit. 



There are, then, plants, in which the stimulation caused by the larva 

 of a parasite produces the same effect as the stimulation caused by the 

 embryo. 



But to return to the bacteriophage; the bacteriophage corpuscle 

 certainly penetrates the interior of the bacterium and multiplies there. 

 It may be that the presence of the bacteriophage corpuscles within the 

 interior of the bacterium causes reactions of the same type as those 

 normally induced by the presence of the spore, that is to say, an auto- 

 dissolution of the parasitized bacterium. The bacteriophage would 

 then utilize for its metabolism the autolysed substances or at least, 

 some of them. 



This new conception of the mode of action of the protobe does not 

 apply solely to the bacteriophage, but in general to all of the infravisible 

 viruses which are invariably intracellular parasites. 



Immunity in the cell attacked may be of one of two kinds, depending 

 upon which of one of two processes becomes operative; a relative im- 

 munity depending on an adaptation to the stimulating action of the 

 parasite, an adaptation which may progress even up to the point of a 

 symbiosis, or a complete immunity, consisting in a digestion of the 

 parasite. 



III. The third possible hypothesis dealing with the mode of action 

 of the bacteriophage assumes that the bacteriophage itself elaborates 

 ferments which dissolve the substance of the bacteria, thus utilizing 

 the substance of the bacteria for its development. 



By analogy with the behavior of other living beings this hypothesis 

 is the first to come to mind, but analogy most assuredly is not proof, 

 and it may well be that in these rudimentary beings, occupying the very 

 first step in the sequence of living creatures, behavior may be different. 



