UNICITY OF BACTERIOPHAGE PROTOBE 367 



different from those of all other races their definition accords perfectly 

 with what I have maintained consistently from the beginning of my 

 studies, when I alone was occupied with the question. This interpreta- 

 tion I have adhered to throughout. Here is, in extenso, a passage from 

 one of my papers published in 1919.^^^ 



I have stated above that I have not yet isolated two races of the bacteriophage 

 which are absolutely identical. The differences consist in the extent of their ac- 

 tion and in its intensity. When derived from the body some strains will be en- 

 dowed with a bactericidal power for several of the intestinal bacilli; for example, 

 they will attack, with different degrees of intensity, all of the dysentery bacilli, 

 the typhoid bacillus, the paratyphoid strains, and B. coli; other strains will 

 attack only a single bacterial species to the exclusion of all others, and a third 

 race may attack two, the Flexner dysentery bacillus and paratyphoid B, for 



example. All possible combinations may occur And, since all possible 



combinations may be presented both as to extent and as to intensity, it may 

 readily be understood that it is quite possible that millions of strains of the 

 bacteriophage may be isolated before two are encountered which are identical. 



I do not believe that I can express more clearly the idea that each 

 strain^ — each race — possesses particular characters. 



When these authors who support the idea of the "plurahty of bacterio- 

 phages" take exception to this conception, that is, to the idea of a 

 plurality of races which I was the first to observe, it can only mean that 

 they affirm that there is a plurahty, not of bacteriophages, but of species. 



In order to avoid all confusion let me repeat that I affirm that the 

 fact of variability, which can be induced experimentally within a single 

 race, coupled with the fact of multiple virulences, shows that the differ- 

 ences between different races may be derived through adaptation, and 

 that, in accord with the conditions of the moment, a "Shiga-bacterio- 

 phage" may be transformed into a ''Staphylo-bacteriophage" or into 

 a 'Testis-bacteriophage," in just the same way as by passages a "horse 

 streptococcus" becomes a "rabbit streptococcus" or a "mouse 

 streptococcus." 



What, then, are the arguments advanced by these authors in support 

 of their concept of plurahty, that is, their behef that a Shiga-bacterio- 

 phage must remain a Shiga-bacteriophage always, that a Pestis-bacterio- 

 phage will never attack anything but B. pestis, and who affirm, in brief, 

 to use the very expression of Bruynoghe,- — the champion of the plurahty 



This plan has been followed simply for the sake of convenience and to avoid repeti- 

 tion and possible confusion. The implied meaning given to these terms, is, how- 

 ever, precisely that which ordinary usage accords them. 



