208 THE BACTERIOPHAGE AND ITS BEHAVIOR 



bacteria. If one suspends all of such a colony and inoculates this sus- 

 pension with bacteriophage corpuscles the more highly resistant bacteria 

 will not be attacked, but will multiply while the less resistant bacteria 

 are parasitized and this permits a simultaneous multiplication of the 

 bacteriophage corpuscles. 



As for the resistant colonies contaminated by corpuscles, colony 

 isolation shows that, like the secondary culture from which they were 

 derived, they form ultrapure colonies of varied resistance as well as 

 contaminated colonies. 



We have seen that in a suspension of bacteriophage corpuscles each one 

 possesses its own virulence, one corpuscle differing from another. We 

 also know that in a suspension of susceptible bacteria each organism 

 presents a capacity for resistance which varies from one bacterium to 

 another. We now find that in a secondary culture each of the bacteria 

 have a special resistance, varying from one to another. It is these 

 variations which render biological phenomena so complex and which 

 render their study so difficult. 



8. MIXED CULTURES 



We have seen what takes place if a secondary culture is subcultured 

 by means of isolated colonies. What happens if the subculturing is 

 made "in toto," that is to say, if a drop of a secondary culture is removed 

 and implanted into sterile bouillon, or if a portion of a contaminated 

 colony is transferred to either a tube of bouillon or to an agar slant? 



When one inoculates bouillon with a secondary culture "en bloc" or 

 with a contaminated colony from agar the medium frequently remains 

 sterile. In such a transfer the bacteriophage is introduced and bacterio- 

 phagy takes place with the young bacteria derived from the multiplica- 

 tion of the bacteria implanted. Sometimes on the agar slant or in the 

 bouillon it is the bacteria which prevail. Due to their resistance they 

 develop in spite of the bacteriophage corpuscles which are present and 

 under these conditions the cultures can be recultivated indefinitely 

 (Bordet and Ciuca^' as well as Kuttner.^^^) It is, indeed, possible to so 

 arrange things that the bacterium will always prevail. To accomplish 

 this it is only necessary to modify the conditions in such a way as to 

 provide an unfavorable environment for the corpuscles. This is what 

 happens in a liquid medium when one introduces the bacteriophage into 

 a medium containing a sugar fermented by the bacteria. Acid is 

 formed, and as is known, bacteriophagy takes place with difficulty in 

 such a medium. Upon a solid medium an inhibitory influence is provided 



