240 THE BACTERIOPHAGE AND ITS BEHAVIOR 



lent corpuscles the agar often remains sterile (d'Herelle^^^). When 

 colonies form some are ultrapure, others are contaminated by corpuscles 

 (Kuttner^^^). Among the ultrapure colonies some are composed of 

 susceptible bacteria, others of resistant bacteria (Bordet and C'uca^'), 

 and the degree of resistance is in its nature variable from one colo y to 

 another (Bruynoghe^^-). 



8. The transfer of a secondary culture to bouillon yields, in cases 

 where growth occurs, a mixed culture in which resistant bacteria and 

 virulent corpuscles co-exist (Bordet and Ciuca,^'' Kuttner^^^). The 

 appearance of mixed cultures in bouillon differs in accord with the 

 virulence of the bacteriophage which they contain. In order that there 

 may be a permanent mixed culture, that is to say, one indefinitely 

 transferable in the form of a mixed culture without either of the two 

 antagonists predominating, it is necessary that a state of equilibrium 

 be established between the resistance of the bacteria and the viru- 

 lence of the bacteriophage corpuscles. If, as the result of circumstances, 

 this equilibrium is not attained one or the other of the two antagonists 

 will be eliminated. 



9. Secondary cultures result from an inhibition of the bacteriophage 

 corpuscles by substances secreted by the bacteria which are reacting 

 to the action of the bacteriophage. Inhibition is most outspoken when 

 the corpuscles are of low virulence (d'Herelle). 



Through the influence of the reaction opposed by the bacteria to the 

 bacteriophage mutations are produced. These are almost always 

 transitory, disappearing along with the cause which produced them 

 (Eliava and Pozerski^^^), but occasionally permanent. These muta- 

 tions may involve all of the characters of the bacterium; among others, 

 morphology (d'Herelle^^^), biochemical characteristics (d'Herelle-^^O^ 

 agglutinability, which is usually diminished (d'Herelle^^^), vitality, 

 which is usually increased (d'Herelle^-^) , or virulence, also usually 

 increased (Bordet and Ciuca^^) but sometimes abolished (Fejgin^*^!). 



With regard to morphology, bacilli in a state of active resistance take 

 a cocco-bacillary form, even assuming a definite coccus form. They 

 become surrounded by a capsule (d'Herelle'^*) . When the bacteriophage 

 is eliminated there is usually a return to normal form (Eliava and 

 Pozerski^^'). Nevertheless it appears that under certain undetermined 

 conditions a fixed mutation involving morphology may take place. 



10. Under the influence of the acquisition of resistance there occurs 

 under certain conditions infra-visible forms of resistant bacteria 

 capable of reproducing the ordinary visible form (Izar^"). These 



