432 THE BACTERIOPHAGE AND ITS BEHAVIOR 



presence in this filtrate of a single race of the bacteriophage or to the 

 presence of several different races. 



All of the experiments made to this end have been conducted in the 

 same manner. First, the activity of the filtrate on different bacterial 

 species was determined, and then a series of 10 to 12 passages with the 

 bacterium for which the activity proved to be the strongest was made. 

 This procedure for increasing the virulence was followed by spreading 

 the bacterium-bacteriophage mixture on agar. From these cultures 

 three plaques were selected and inoculated into three bacterial sus- 

 pensions, always of the same bacterium at the expense of which the 10 

 or 12 passages had been made. Finally, selective isolations in bouillon, 

 by the inoculation of single corpuscles were made. 



Being thus certain that pure races had been obtained, I ascertained 

 the different virulences of each of the three plaques. 



Naturally, for these tests I selected filtrates active for different species 

 of bacteria. The results follow. 



1 . Bacteriophage from the horse (Phantiet) 



This filtrate had been held in a sealed ampoule for two years. When 

 tested for its virulences it showed : 

 B. coli*+ + 



B. dysenteriae Shiga ++ + 

 B. dysenteriae Flexner + + + 

 B. dysenteriae Hiss + + 

 B. paratyphosus B + 

 After the virulence had been increased by means of passages with 

 B. dysenteriae Shiga, and the purification procedure had been effected, 

 determinations made with the three plaques isolated gave : 



Plaques 

 1 2 3 



B.coli ++ ++ + + 



B. dysenteriae Shiga + + + + + + + + + + + + 



B. dysenteriae Flexner + + + + + + + + + + + + 

 B. dysenteriae Hiss + + + + + + 



B. paratyphosus B + + + + + 



From this we can only conclude that the activity of the original filtrate 

 was due to the multiple virulences of but a single race of the bacterio- 

 phage. 



* The strain of B. colt used in this study, and in those which follow was a very 

 susceptible old stock strain. 



