176 



THE BACTERIOPHAGE AND ITS BEHAVIOR 



by passages, a virulence for a bacterium toward which it previously 

 manifested no activity. In the first edition of my collected papers^^^ 

 experiments were presented supporting this idea. Since that time a 

 great many authors have confirmed this fact. The contributions of 

 Otto and his collaborators in particular present many experiments dem- 

 onstrating the truth of this idea. But I will mention here only the 

 following, for these experiments are extremely interesting from the 

 theoretical point of view since they show how the virulence of the bac- 

 teriophage is acquired under natural conditions, and from the practical 

 point of view they are significant in that they indicate a procedure par- 

 ticularly well adapted to bring about, experimentally, such an acquisi- 

 tion of virulence. 



* The method employed by Janzen and Wolff for measuring virulence has been 

 described. In the tables given here, dissolution refers to bacteriophagy in a 

 fluid medium; inhibition to a retardation of growth when the bacteriophage is 

 added to a seeded medium; and plaques, of course, refers to the formation of these 

 areas upon agar. 



Janzen and Wolff were the first to show that a race of Typhoid-bac- 

 teriophage, manifesting at its isolation a virulence for certain strains of 

 B. typhosus and at the same time completely avirulent for others, was 

 able to acquire a definite virulence for some of the latter strains, and 

 this simply by means of passages at the expense of certain susceptible 

 strains. I am including here two of their experiments.*^^ 



The virulences of the bacteriophage involved were determined for 5 

 different strains of B. typhosus immediately after its isolation from the 

 intestinal tract and again after a series of passages with a single strain 

 of the typhoid bacillus. The results obtained with bacteriophage 

 race Re, are shown in table 14. 



Additional data are given for bacteriophage, race Wi (table ] 5) . 



The results are essentially these: bacteriophage Re, by virtue of 

 passages at the expense of typhoid strain Sm has acquired a virulence 



