226 THE BACTERIOPHAGE AND ITS BEHAVIOR 



We have seen in a previous chapter that the first phase of bacteri- 

 ophagy consists in the fixation of bacteriophage corpuscles to the bac- 

 terium. Fixation takes place in the same way with bacteria which have 

 acQuired a refractory state (Flu).^^^ 



11. ULTRABACTERIA 



Working with a Coli-bacteriophage Izar^ ^ has seen that "if the clear 

 liquid obtained by filtering a culture of B. coli dissolved under the action 

 of the bacteriophage is seeded in bouillon or upon agar immediately 

 after filtration it does not cause either turbidity or growth if it is pro- 

 tected from the air in sterile tubes which are completely filled and sealed 

 in the flame. But if the filtrate is held in sterile tubes closed with 

 cotton or in tubes which are only partly filled, in many cases coccobacilli 

 develop after a period varying from 48 hours to 11 days." 



I also have found that suspensions obtained by the filtration, through 

 Chamberland L2 or L3 candles, of bacteriophage suspensions of B. 

 dysenteriae Shiga, Flexner, or Hiss, of B. typhosus, of B. pestis, of B. 

 gallinarum and of B. coli may become cloudy again. The period of 

 time required for the appearance of this phenomenon varies and I have 

 found that the cause of the turbidity is the growth of resistant bacteria. 

 This observation is recorded in a note appearing in the first edition of 

 the "Bacteriophage." It reads as follows: 



The following suggests that under the influence of the bacteriophage non- 

 spore-forming bacteria may give rise to filterable forms. I have noted, although 

 rarely, that a filtrate obtained by passing a secondary culture through a Cham- 

 berland bougie (L2 and even L3) becomes turbid after some days. Each time 

 that this has been noted the turbidity has been due to the growth of a resistant 

 bacterium such as was present in the secondary culture prior to the filtration. 

 The conditions under which this phenomenon occurs have not been ascertained, 

 thus the observation is simply mentioned without emphasis being placed on its 

 interpretation. 



In what follows I shall term these filtrable forms of bacteria "ultra- 

 bacteria." 



Tomaselli^^^ has studied the conditions leading to the appearance of 

 these ultrabacteria and has made an important contribution to our 

 knowledge of this curious phenomenon. 



He has shown that the difficulty which is sometimes experienced in 

 increasing the virulence of a bacteriophage for certain bacterial strains 

 is due to the fact that resistant ultrabacteria pass through the candle. 



We have seen, as a matter of fact, the mechanism of the increase in 

 virulence of the bacteriophage. Corpuscles having a weak virulence 



