202 THE BACTERIOPHAGE AND ITS BEHAVIOR 



evident that the attenuation of the virulence of a bacteriophage takes 

 place only when the resistance of the bacteria dominates the virulence. 

 In the opposite case, when the resistant bacteria are overcome there 

 results, naturally, an increase in virulence. A bacteriophage, when 

 overcome, is attenuated. A bacteriophage when overcoming is 

 enhanced and the increase in virulence is in direct proportion to the 

 resistance of the bacterium overcome. Whether these events take 

 place in the scale of beings that involve the susceptible animal and the 

 virulent bacterium or the susceptible bacterium and the virulent bac- 

 teriophage is of no fundamental significance. The result is exactly the 

 same. 



Some experiments of Gratia and of Wollstein illustrate particularly 

 well the increase in virulence resulting from the contact of a victorious 

 bacteriophage with bacteria which have acquired a resistance.^^® A 

 bacteriophage at its time of origin presented a specific activity, limited 

 to a single strain of B. coli. Successive passages were made at the 

 expense of resistant bacilli of this same strain. The results are sum- 

 marized in table 18 (+ + + + = complete bacteriophagy, no resistant 

 colonies forming when the material is spread upon agar; 4- + + = 

 almost complete dissolution, less than 12 colonies developing when 

 spread upon agar; +-F = partial dissolution, many resistant colonies 

 appearing; + = no dissolution, a few plaques forming when spread upon 

 agar; — = no bacteriophagy; S = the susceptible strain, R = the resist- 

 ant strain). 



the peritoneum of a guinea-pig. After a few hours he removed the peritoneal 

 exudate and centrifuged it at moderate speed, the leukocytes, together with the 

 phagocytized bacteria, collecting in the sediment. The free bacteria, i.e., those 

 which had resisted phagocytosis, remained suspended in the supernatant 

 fluid. With these materials he inoculated two guinea-pigs intraperitoneally. 

 To one he gave a few drops of the supernatant fluid, containing, of course, "vic- 

 torious" bacteria, and to another he gave a portion of the sediment containing 

 phagocytized bacteria, that is to say, "conquered" organisms. He continued 

 these passages in a double series and demonstrated that the virulence of the strain 

 resulting from the selection of the "victorious" bacteria increased with each 

 passage and ended by being very high. On the contrary the strain resulting 

 from the selection of "conquered" bacteria became more and more attenuated. 

 It is only necessary to substitute in the experiment of WoUmann the word 

 "guinea-pig" or better yet "leukocytes of the guinea-pig" by "bacterium" and 

 the word "bacterium" by "bacteriophage corpuscle" in order to realize how 

 completely the facts observed by him conform to the behavior of the 

 bacteriophage. 



