PROPERTIES OF THE BACTERIOPHAGE 



285 



typhosus 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 

 examined again, with the results shown in table 26. 



In this material the virulence of the bacteriophage for B. dysenteriae 

 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. 



TABLE 26 



It should be noted that the result was the same whether the bac- 

 teriophage was preserved directly in feces or in the filtrate, that is, in 

 bouillon. Likewise, in this instance, it is significant that the degree 

 of virulence has no influence on the preservation or the disappearance 

 of the virulence. It was strong for B. typhosus and became negative, 

 it was weak for B. paratyphosus B, yet this remained intact. 



In the absence of passages, simply as an effect of old age, the virulence 

 of the bacteriophage varies then with time, and indeed in a different 

 manner for the diverse bacteria attacked. It becomes attenuated 

 more quickly for some than for others, and for this no general rule can 

 be fixed. We have seen elsewhere that after four years and in spite of 

 passages in contact with the dysentery bacillus, the virulence for B. 

 typhosus persisted. The last experiment cited is not only interesting 

 then, in that it shows an attenuation of virulence associated with the 

 lapse of time, but also in that it gives evidence that the loss does not 

 occur in equal degrees for all of the bacteria attacked by one and the 

 same bacteriophage. 



