VIRULENCE OF THE BACTERIOPHAGE 179 



susceptible bacterial species, bacteriophagy occurs, but not all of the 

 organisms are attacked with the same intensity. Bacteriophagy is 

 complete for the species toward which the virulence is maximal or very 

 high, it is partial for others, and is, indeed, the less marked as the viru- 

 lence for the organisms is the less pronounced. As a matter of fact, 

 whether the bacteriophage acts upon different susceptible organisms 

 separately or whether it acts upon mixtures of these bacteria, the 

 attack occurs in just the same manner. 



It is rather interesting that it appears that the virulence for bacteria 

 which are attacked but weakly may be increased more rapidly in com- 

 bined cultures, as is indicated by the following experiment. 



Three tubes of bouillon receive respectively 0.01, 0.1, and 1 cc. of a 

 known Shiga-bacteriophage. The thi'ee tubes are then Hghtly planted 

 with B. coli. Normal cultures develop in the three tubes. Platings 

 on agar give few plaques. Each of the three cultures is transferred to 

 fresh bouillon. Normal B. coli cultures develop. Transfers to agar 

 give two plaques for the first tube, none for the other two. The culture 

 yielding the two plaques is again re-inoculated. A normal culture 

 develops. The bacteriophage has been eliminated. 



This strain of Shiga-bacteriophage possesses, therefore, an extremely 

 feeble virulence for the strain of B. coli under test. 



To 10 cc. of bouillon is added 1 drop of a concentrated suspension of 

 Shiga bacilli (this should give a slight turbidity equal to about 50,000,000 

 bacilli per cubic centimeter) and 1 drop of an equally concentrated 

 suspension of B. coli. This double suspension is then inoculated with 

 0.01 cc. of the Shiga bacteriophage used in the above experiment. 



After twenty-four hours there is a slight turbidity. A new passage 

 into a double Shiga-Colon suspension is made. Perfect dissolution 

 takes place after eleven hours. 



The dissolved suspension is then introduced, in a quantity of 0.04 cc, 

 into a simple suspension of B. coli. Dissolution is complete in seven 

 hours. 



The corpuscles have developed at the expense of the Shiga bacilli, 

 and thus being maintained in the medium they have gradually acquired 

 a virulence for B. coli (d'Herelle^-^). 



RJESUME 



The multiplication of bacteriophage corpuscles belonging to differ- 

 ent races does not take place with the same intensity, even though the 

 conditions for the process are identical for all. The activitv — the 



