102 



THE BACTERIOPHAGE 



When a bacteriophage is virulent, as it comes from the organ- 

 ism, for several bacteria at the same time, as is the usual case, it 

 is apparent that the virulence present for each of these bacteria 

 is subject to variations with time. This is true, however, the 

 virus may be preserved, whether it is kept, sealed in tubes, in the 

 original intestinal contents or whether it is preserved in the form 

 of filtrates prepared from the fecal material. 



When kept in vitro certain strains of bacteriophage lose their 

 virulence for a bacterium, toward which they were active when 

 derived from the body, much more rapidly than do others. 



Experiment XXIX. Typhoid patient Mor Examination 



of the stool was made at the beginning of convalescence. On August 

 20th, 1918, the stool was treated according to the method described for 

 securing the bacteriophage. The filtrate is distributed in 0.5 cc. amounts 

 in suspensions of the following bacteria : B. dysenteriae Shiga, B. typhosus, 

 B. paratyphosus A, B. paratyphosus B, and B. coli. After 24 hours of 

 incubation these suspensions were planted on agar with the following 

 results : 



B. dysenteriae Shiga Sterile 



B. typhosus Sterile 



B. paratyphosus A Numerous plaques 



B. paratyphosus B Numerous plaques 



B. coli Sterile 



Specimens of the feces and of the filtrate were preserved in sealed tubes. 

 On January 22nd, 1919, that is, after 5 months, these materials were exam- 

 ined again: 



In this material the virulence of the bacteriophage for B. dys- 

 enteriae and for B. paratyphosus B remained unaltered during 

 the five months, it diminished for B. coli, and disappeared entirely 

 for B. typhosus and B. paratyphosus A. 



