222 



THE BACTERIOPHAGE AND ITS BEHAVIOR 



These mutations of B. coli have been studied quite extensively, thanks 

 to the work of Bordet, and of Gratia especially. It is certain that a 

 study of the mutations of other bacterial species brought about through 

 the action of the bacteriophage will reveal many surprising things. It 

 is, indeed, probable, as various investigators have suggested, that all 

 of the fixed mutations occurring among bacterial species are produced 

 through the action of the bacteriophage.* 



The formation of a capsule through the action of the bacteriophage 

 appears to be a most constant phenomenon accompanying the state of 



high resistance to the bacteriophage. It is particularly clear-cut in 

 the bacteria composing the small mixed colonies which can be observed 

 after spreading upon agar a secondary culture in which very virulent 

 corpuscles and very resistant bacteria co-exist (d'Herelle) .^^^ The capsule 

 usually disappears in the first transplant in the ultrapure colonies. 

 However, it appears that under conditions not yet known a stable muta- 



* We must not forget to mention the kindly and too little known Noel Bernard 

 when the question of mutations occurring because of symbiosis are considered, 

 that is to say, when they occur through the effects of a mitigated parasitism. 

 This scientist has shown that in the plants symbiosis is the primary cause of 

 fixed mutations. 



