94 THE BACTERIOPHAGE 



virulence. These ultramicrobes develop slowly, but at the same 

 time the very numerous bacteria have had time to adapt them- 

 selves and to elaborate a defensive mechanism to the lysins se- 

 creted into the medium. They have produced an antilysin which 

 paralyzes the action of the bacteriophage. Moreover, it has been 

 shown that these antilysins are specific, for those secreted by the 

 dysentery bacillus are without inhibiting action on the lysis of 

 B. pestis. 



The bacteria, in general, react like higher organisms. B. tetani, 

 for example, secretes a toxin, and an animal which would be killed 

 by a large dose of this toxin reacts to a small dose by the produc- 

 tion of an antitoxin which will neutralize the toxin. The bacterio- 

 phage secretes a lysin and the bacterium, which could not resist 

 a rapid attack, produces, when placed in favorable conditions, an 

 antilysin which neutralizes the action of the lysin. 



We will further see that the organism reacts to the injection of 

 the bacteriophagous lysins, which in effect, are nothing but foreign 

 bodies of the same nature as the toxins, 9 and, indeed, in a manner 

 quite analogous to that of the bacteria, namely, by the production 

 of specific antilysins. 



MULTIPLE CULTURES 



It remains for us to consider multiple cultures. In the following 

 chapter we will see that the virulence of a strain of bacteriophage 

 is rarely limited to a single bacterial species. What forms do 

 secondary cultures take when a bacteriophage is forced to act 

 upon a suspension comprising different bacterial species? We 

 will confine ourselves to the most simple case, — a bacteriophage 

 reacting upon two species of bacteria. Let us take as an example 

 a strain of bacteriophage very virulent for B. dysenteriae Shiga 

 and but slightly virulent for B. coli, as evidenced in the following 

 experiment. 



Experiment XXVI. Three tubes of bouillon receive respectively 0.01, 

 0.1, and 1 cc. of a known anti-Shiga bacteriophage. The three tubes are 

 then lightly planted with B. coli. Normal cultures develop in the three 

 tubes. Platings on agar give few plaques. Each of the three cultures is 



9 The organism does not defend itself against a toxin because it is toxic 

 but because it acts as a foreign colloid in the body. 



