250 



THE BACTERIOPHAGE AND ITS BEHAVIOR 



may acquire new virulences. We have already seen that by repeated 

 contacts it is possible to cause a bacteriophage to acquire a virulence 

 for new species. Here the case is the same, for insofar as the bacterio- 

 phage is concerned, different strains of a heterogeneous species behave 

 like distinct species. 



Janzen and Wolff^^^"^ present some additional data dealing with 

 the virulence of Bacteriophage Wi when tested upon 5 strains of B. 

 typhosus. When this bacteriophage was tested immediately after its 

 isolation from the intestinal tract the results were as shown in table 22. 

 When tested again after a series of passages at the expense of the Wi 

 strain the results were as given in table 23. 



From this it appears that with this bacteriophage the reactions were 

 exactly the same when tested immediately after its recovery from the 

 body where it had undergone passages at the expense of strain Wi 

 which was isolated from the patient, and when tested later after passages 

 in vitro at the expense of this same typhoid bacillus. Whether the 

 passages had taken place m vivo or in vitro the behavior of the bac- 

 teriophage was the same. 



Janzen and Wolff then subjected this bacteriophage to passages at 

 the expense of strain Sm. After 10 passages the reactions were as 

 shown in table 24, This shows definitely that by a series of passages 

 at the expense of strain Sm the race had acquired a virulence for strain 

 1, and the virulence for strain 29 had been increased. 



Several authors have obtained comparable results. Of those who 



