196 THE BACTERIOPHAGE AND ITS BEHAVIOR 



5. THE BEHAVIOR OF THE BACTERIOPHAGE IN SECONDARY CULTURES 



The way in which the bacteriophage behaves in secondary cultures 

 involves a number of very interesting pecuharities. 



We have seen that a single bacteriophage corpuscle, provided it is 

 endowed with a high virulence, may cause complete bacteriophagy in a 

 normal bacterial suspension and dissolution is still more certain if the 

 suspension is somewhat less dense. Dissolution of the bacterial cells is 

 complete. If one simply seeds the bacterium into bouillon inoculated 

 with a single very virulent corpuscle there is a simultaneous develop- 

 ment of a culture of the bacteria and of the corpuscles. When the latter 

 have become sufficiently abundant to parasitize each of the young bac- 

 teria, dissolution occurs rapidly and the medium becomes clear. 



Under all circumstances, then, the introduction of a single corpuscle 

 of maxunum virulence into a medium containing from 1 to 250,000,000 

 susceptible bacteria per cubic centimeter leads to a complete bacteri- 

 ophagy, and secondary cultures never appear, provided the conditions 

 are optimum for bacteriophagy, that is to say, provided the medium 

 has a pH greater than 7.6 and the temperature is lower than 32°C. 

 Furthermore, in all such cases the corpuscles derived from the single 

 corpuscle also have a maximum virulence. 



With a bacteriophage of high, but not maximum, virulence the inocu- 

 lation of a single corpuscle causes a bacteriophagy manifesting itself in 

 the same manner as the preceding, but with further incubation a second- 

 ary culture always develops in the medium which had previously become 

 completely cleared.* 



Let us, then, observe the course of bacteriophagy as it takes place 

 when a single corpuscle of high virulence is inoculated into a series of 

 tubes each containing 10 cc. of a normal suspension of susceptible bac- 

 teria.f When bacteriophagy is complete and secondary cultures appear 

 separate these suspensions in which the phenomenon has taken place 

 into two groups. Filter the first group immediately while the medium 

 is still clear. With the second group allow secondary cultures to form 

 and filter them after a few days. 



Comparing the two filtrates it will be found that the number of bac- 

 teriophage corpuscles is practically the same in both, but while those 

 of the first filtrate have a very high virulence, equal to that of the original 

 corpuscles, the virulence of the second filtrate is attenuated. If pas- 



* See the section "Evaluation of Virulence." 



t Following the technic which has been described, distributing 10 cc. of the 

 last active dilution into 10 suspensions, 1 cc. per tube. 



