NATURE OF BACTERIOPHAGE 



335 



Janzen and Wolff"^'"^ have taken advantage of this pecuharity to 

 demonstrate the autonomy of the bacteriophage with reference to the 

 bacterium, and their experiments are worthy of consideration. 



They selected three races of the Typho-bacteriophage, attacking the 

 different strains of B. typhosus, Re, Wi, and Sm. They maintained 

 these three bacteriophage races with a single strain of B. typhosus 

 (strain Sm, isolated from the stools of the patient who furnished the 

 bacteriophage Sm). After a series of passages, all contacts being 

 made with B. typhosus Sm, determinations of the activity of the three 

 races for a number of typhoid strains showed the results in table 31.* 



It is very evident that if the bacteriophage were a bacterial product 

 the three races of the bacteriophage should have become uniform, since 

 all three developed during several passages at the expense of the same 



TABLE 31 



bacterium, B. typhosus Sm. But, as the experiment shows, this was not 

 the case. Each bacterium retained its own characteristics and again it 

 follows that the bacteriophage is an autonomous being, possessing its 

 distinctive characters, independent of the bacterium at whose expense 

 it has developed. 



With regard to the characters of these races of the bacteriophage, 

 Janzen and Wolff made an interesting incidental observation. They 

 asked me to give them such races of the Typho-bacteriophage as I had 

 in my collection. I sent them six tubes of the bacteriophage, marked 

 Tv^, Tv^, Tv^, rv^, Tv^, and ru^.f Some time later they asked me if I 



* For the method of determining the degree of virulence of a bacteriophage see 

 the section "Appreciation of Virulence." In the method employed by Janzen 

 and Wolff three indices of activity were used: inhibitory power, dissolving power, 

 and the formation of plaques on agar. 



t For the sake of simplicity I have adopted the custom of designating the 

 bacteriophages by the initial letter (Greek) of the bacterium for which the viru- 

 lence was the strongest when the race was isolated. For example, 5 indicates a 

 Shiga-bacteriophage, a^p a Staphylo-bacteriophage,ri;, a Typho-bacteriophage, x a 

 Coli-bacteriophage. To this is added the number of the race. 



