170 THE BACTERIOPHAGE AND ITS BEHAVIOR 



several species, albus, aureus, and citreus. As a matter of fact, with 

 this particular race I have not yet found a typical staphylococcus which 

 is not attacked, even Micrococcus tetragenus is dissolved. 



We will return to this question of homogeneous and heterogeneous 

 bacterial species when we study the peculiarities of the phenomenon of 

 bacteriophagy with the different bacterial species. We will then review 

 the studies of Janzen and Wolff, particularly those dealing with the bac- 

 teriophagy of the heterogenous B. typhosus. 



8. MULTIPLE VIRULENCES OF THE BACTERIOPHAGE 



We have seen that certain races of the bacteriophage are virulent 

 for only a single bacterial strain, while others are virulent for all strains 

 of a given species. Furthermore, we have stated that still other races 

 are virulent not only for all strains of a single species but also for strains 

 of bacteria belonging to different species, sometimes to species rather 

 remotely related (d'Herelle^^^). As a matter of common observation it 

 has been found that a given race of the bacteriophage, when derived 

 from the organism, is rarely active for but a single bacterial species. 

 Usually at this time it attacks a number of species and possesses for 

 each of them a varying degree of virulence (d'Herelle^^^). 



Such a race of the bacteriophage might have, for example, a very 

 high virulence for the Hiss strain of B. dysenteriae, a moderate virulence 

 for some strains of B. coli, and a low virulence for other strains of B. 

 coli as well as for the Shiga bacillus. For B. paratyphosus B the action 

 may be very weak, and for other species no virulence whatever can be 

 demonstrated. Another race may be very active for certain strains of 

 B. coli and of B. typhosus, less virulent for other strains of these or- 

 ganisms, and at the same time it may show but little activity for B. 

 dysenteriae Flexner with no virulence for all other bacterial species. 

 But provided an activity, even though weak, is manifested by such a 

 race it is always easy, by passages, to enhance the virulence for one of 

 these organisms. 



We have seen further that because of variations in virulence a given 

 race of the bacteriophage may vary materially at different times. All 

 of the combinations of virulence, in quality as well as in quantity, being 

 possible, that is to say, in the range of the action against various bacterial 

 species and in the intensity of the action for each of the strains of these 

 different species, one can readily understand, in view of the infinite 

 number of possible combinations, that there can be no two races of the 

 bacteriophage which can be absolutely identical (d'Herelle^^^). 



