BACTERIA SUSCEPTIBLE TO BACTERIOPHAGY 263 



implanted with laboratory strains of the cholera vibrio. After an incubation 

 period of from 2 days to 1 week the liquid should be examined for its action upon 

 the laboratory strains of the vibrio. 



It might be added that after some 10 passages according to the pro- 

 tocols given by Flu, he obtained a complete dissolution of a suspen- 

 sion containing 200 million cholera vibrios per cubic centimeter within 

 a period of from 3 to 5 hours at a temperature of 37°C. Within 1 to 

 2 hours after the liquid became completely cleared, the medium again 

 began to become clouded because of the formation of a secondary culture 

 and a few hours later the medium was as turbid as was the culture control. 



In a word, then, with the race isolated by Flu dissolution was very 

 rapid; as rapid as is the bacteriophagy of B. dyscnteriae under the action 

 of a bacteriophage of maximum virulence. But secondary cultures 

 began to develop almost immediately. If one waits about 12 hours 

 (as I had done in Indo-China where I observed the suspensions inocu- 

 lated in the afternoon on the following morning) in order to determine 

 if bacteriophagy has occurred, the secondary culture already developed 

 will lead one to think that he is dealing with a normal culture. 



It does not appear, however, that with all races of the bacteriophage 

 virulent for the cholera vibrio secondary cultures develop quickly, 

 Eliava has informed me that in 1918, before he had seen any published 

 work upon the subject of bacteriophagy he had observed during an epi- 

 demic period, that certain specimens of water from the river Koura 

 which passes Tiflis brought about a complete and permanent dissolution 

 of cultures of the cholera vibrio. In these cases, then, secondary cul- 

 tures did not occur. Whether they do, or do not develop is simply a 

 question of the virulence of the race of bacteriophage. Moreover I have 

 noted that as a usual thing the virulence of bacteriophage races isolated 

 from old naturally mixed cultures is never strongly enhanced by passages 

 with a susceptible bacterium. Usually the virulence becomes fixed at a 

 moderate value, rarely very high, beyond which it is impossible to 

 increase it. There are, indeed, few races of the bacteriophage which are 

 capable of acquiring a maximal virulence. This is, as a matter of fact, 

 a general law applicable to the virulence of pathogenic bacteria as well 

 as to the bacteriophage ; not all strains or races are capable of becoming 

 enhanced to the same degree. 



When a suspension inoculated with a few corpuscles is spread upon 

 agar characteristic plaques appear after incubation. 



The virulence of the bacteriophage isolated by Flu extended over a 

 great many strains of vibrio, but he found, nevertheless, ultrapure, 

 naturally resistant strains. 



