CHAPTER III 

 Virulence of the Bacteriophage 



Multiple Virulence. 

 Persistence of Virulence. 

 Bacterial Species Attacked. 



MULTIPLE VIRULENCE 



A strain of bacteriophage freshly derived from the body is 

 rarely active against a single bacterial species. Usually it at- 

 tacks a certain number of species at this time, and possesses for 

 each of these a variable virulence. 



It may be objected that this by no means opposes the concep- 

 tion of a plurality of species in the genus Bacteriophage, each 

 species acting against a determined bacterium. This question 

 will be considered in detail in a later chapter. For the time being, 

 however, it will only be stated that all experimental work, par- 

 ticularly the work with the complement fixation reaction, favors 

 the idea of unicity, whatever may be the origin of the 

 bacteriophage. 



There is but one bacteriophage, but as isolated from the or- 

 ganism, there is an infinite number of strains, each possessing the 

 capacity to attack diverse bacteria. Such a strain may possess, 

 for example, a very high virulence for B. dysenteriae Hiss, an 

 average virulence for B. coli, & low virulence for the Shiga dys- 

 entery strain, a very weak activity for B. paratyphosus B, and 

 none 1 for the other intestinal organisms tested. 



Another strain may be very active for B. coli and B. typhosus, 

 but slightly active for B. dysenteriae Hiss, and inactive for the 

 other bacteria tested. 



1 It is evident that when it is stated that a given strain of bacteriophage 

 lacks virulence for such and such a bacterium it must be understood "a 

 virulence such as may be demonstrated by the present technic." Early 

 in my investigations it was possible to detect only those strains possessing 

 a considerable activity; all others were unnoticed. The technic has since 

 been improved, but at the present time it is most certainly not perfect. 



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