CHAPTER III 



The Mechanism of Bacteriophagy 



1. THE corpuscle: obligatory bacteriophage 



Whatever the nature of the medium, in the absence of a susceptible 

 bacterium the bacteriophage corpuscles do not multiply. Nor is 

 multiplication to be observed even though the medium be favorable 

 for the phenomenon if the corpuscles are placed in contact with killed 

 bacterial cells. The method of killing the bacteria is without signifi- 

 cance: the reaction does not take place with bacteria killed by aging, 

 heat, chloroform, essences of thyme, cinnamon or mustard, by alcohol, 

 mercuric chloride, or by carbolic, sulfuric or hydrochloric acids.* 



The living bacterial cell is indispensible for the multiphcation of 

 the bacteriophage corpuscle (d'Herelle*^"). Indeed, it is even essential 

 that the living cell be "normal," that is, not exposed to the action 

 of substances which may modify its characters appreciably even 

 though they do not kill it. It is unnecessary to repeat the experiments 

 bearing upon this point, since they have been considered in Chapter I in 

 the section entitled "Influence of Chemical Conditions on the Phenom- 

 enon of Bacteriophagy." 



It can readily be shown that the phenomenon fails to take place 

 solely because of the disturbing influence of the medium upon the 

 bacterium, for, if the unattacked bacteria are separated by centrifu- 

 gation from the medium and suspended in a pure bouillon they undergo 

 bacteriophagy. With such organisms the reaction is, however, more 

 or less delayed; a fact entirely in keeping with the idea that the "ab- 

 normal" bacteria, now multiplying in a pure medium, become again 

 "normal" and when this happens, become subject to the attack of 

 the bacteriophage. 



What is the nature of this anomalous condition which renders the 

 bacteria unattackable? We will be able to interpret and reply to this 



* This applies only to the multiplication of the bacteriophage corpuscles. A 

 dissolution of the bacterial cells may be effected even if the bacteria are dead. 

 But this last reaction is not in reality bacteriophagy. We will return to this fact, 

 since in several instances the dissolution of dead bacterial cells has led to the 

 erroneous conclusion that bacteriophagy had taken place. ^-'-^^^ 



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