228 THE BACTERIOPHAGE AND ITS BEHAVIOR 



longed and filtered samples after 5, 10, 15, and 20 days,* the filtrates 

 obtained after 5 and 10 days always contained ultrabacteria, those 

 filtrates prepared after 15 days sometimes contained them, while those 

 filtered after 20 days never contained them. 



Instead of making passages every 24 hours one has only to filter the 

 suspensions which have resulted from bacteriophagy after 20 days. The 

 result is that which has been described. From the first passages the 

 virulence of the bacteriophage for strain 4, from weak (+) becomes 

 maximal (+ + + +). The same result is obtained for strain 5 after 

 3 passages. 



It must be then the passage through the filter of resistant ultrabacteria 

 which interferes with the increase in virulence. 



As for strain 5, although the passages had been carried out under the 

 same conditions, the virulence of the bacteriophage could not be in- 

 creased to its maximum, nor could Tomaselli demonstrate the formation 

 of ultrabacteria with this strain. 



Tomaselli has demonstrated the same facts with B, dysenteriae Shiga 

 and Flexner. 



Aside from the conclusions which this author has drawn from his 

 experiments concerning the increase in the virulence of the bacteriophage 

 the following may be stated: 1. The formation of ultrabacteria takes 

 place especially through the action of bacteriophages having a weak 

 virulence. 2. Not all of the strains of a single bacterial species 

 possess the same faculty of assuming the ultrabacterial form. 3. The 

 vitality of the ultrabacteria (at least insofar as bacteria of the colon- 

 typhoid-dysentery group are concerned) is relatively weak. They do 

 not remain viable for more than 15 to 20 days. 



Hauduroy-^^'^^^ has also observed the formation of resistant ultra- 

 bacteria in connection with the bacteriophagy of B. dysenteriae, B. 

 typhosus, and B. coli. He has noted the frequency with which it occurs 

 under the action of bacteriophage races of relatively low virulence. 

 He has found that in the filtrates the ultrabacteria do not appear to be 

 very numerous, for in distributing 200 cc. of a filtrate among 20 tubes 

 with 10 cc. to each tube he has observed the appearance of cultures in 

 only some of the tubes. 



Let us note, however, that it is just as easy to believe that the ultra- 

 bacteria may be very abundant in the filtrates but that only a very few 



* He did not prolong the contact beyond this for he found that the attenuation 

 of the bacteriophage through contact with the resistant bacteria was then very 

 pronounced. 



