238 THE BACTERIOPHAGE AND ITS BEHAVIOR 



bacteria of the same species. But the situation may some times be 

 much more compHcated. I might cite as an example an experiment of 

 Flu,2" for in cases comparable to this the method devised by him may 

 be very conveniently employed. 



Everyone who has noted that it is possible to derive from certain 

 bacterial strains among stock culture collections a bacteriophage active 

 for normal bacteria of the same species has indicated that the isolation 

 was possible only from old cultures and not from cultures recently 

 transplanted. But, as Flu has stated, if the bacteriophage is really an 

 impurity it is evident that the corpuscles must have been present in 

 the previous culture from which the transfer was taken. This being 

 the case they must be introduced into the bouillon when the 

 bacteria are implanted, and consequently the corpuscles must have been 

 present in the young cultures. He has been able to demonstrate this. 



Flu centrifuged a 24 hour bouillon culture of the Y-14 strain, of 

 which we have spoken in a preceding paragraph. He mixed the sedi- 

 ment resulting from the centrifugation with four times its weight of 

 anhydrous sodium sulphate,* and ground the dry mass resulting from 

 this mixture in a mortar. The dry powder was dissolved in water and 

 filtered through a candle. This filtrate contained virulent corpuscles 

 which caused bacteriophagy in a suspension of normal Flexner bacilli. 

 The corpuscles, therefore, were actually present in the young cultures 

 of a naturally mixed strain. 



It should be stated that the sodium sulphate solution must be filtered 

 for the bacteria resist this treatment as do the bacteriophage cor- 

 puscles, and if the resistant bacteria are not eliminated they will develop 

 in the suspension to be used in the test for bacteriophagy and the latter 

 process may then be undetected. 



I have also succeeded in isolating a bacteriophage from young mixed 

 cultures by dissolving the bacteria by pyocyanase. The filtrate con- 

 tained the corpuscles. 



The fact that a mixed culture, either natural or artificial, can be sepa- 

 rated into two parts shows beyond possible contradiction that in such 

 cultures bacteriophage corpuscles represent an impurity, in the bacte- 

 riological sense of the word. 



1. The behavior of bacteria with regard to bacteriophage corpuscles 

 does not escape a general biological law : one which might be termed the 



* This is the method devised by Rowland for the extraction of the toxin of 

 Shiga dysentery bacilli. 



