CHAPTER VI 



Species of Bacteria Susceptible to Bacteriophagy 



1. homogeneous species 



1. B. dysenteriae Shiga (Eherthella dysenteriae) 



The Shiga dysentery bacillus is the first bacterial species which I 

 recognized as being susceptible to bacteriophagy.^^" It is also the bac- 

 terium for which it is most easy to isolate virulent races of the bacterio- 

 phage ; races frequently of sufficient virulence to overcome the organisms 

 without the necessity of enhancing virulence by passages. 



Up to the present time I have isolated several hundred races of the 

 bacteriophage virulent for B. dysenteriae Shiga and I have yet to find two 

 which at the time of their isolation are identical, not only with regard 

 to the intensity of their virulences for this bacterium, but also as to the 

 extent and the degree of their activity for other bacterial species.^^^ 

 All of the races which I have isolated were virulent for all of the strains 

 of B. dysenteriae Shiga against which I have tested them, — strains 

 selected at random either from among stock cultures or obtained from 

 cultures derived from plates spread directly from dysentery cases. 

 A race very virulent for a given strain of the Shiga bacillus may be less 

 active for another strain but after a few passages at the expense of the 

 latter it acquires a virulence comparable to that exhibited toward 

 the first (d'Herelle ^^i). 



Among all of the races which I have studied I have encountered 

 but a single one whose virulence was directed solely toward the Shiga 

 bacillus. All of the others were virulent for one or another of the 

 dysentery bacilli, Flexner or Hiss, and many were active against the 

 two at the same time.^^^ Very few races attack the Strong bacillus. 



A great many races are at one and the same time virulent for a greater 

 or less number of strains belonging to the heterogeneous bacterial species; 

 B. coli, B. typhosus, B. paratyphosus A and B, and other species of this 

 group, and this may be the case immediately after isolation (d'Her- 

 elle '''). 



I will not return to the possibility of acquiring a virulence for bac- 

 terial species very distantly related, such as B. pestis, the staphylococcus, 

 etc., for this question has been treated in detail. 



242 



