186 THE BACTERIOPHAGE AND ITS BEHAVIOR 



contact. Each of these tubes is inoculated with 0.001 cc. of the same 

 culture of bacteriophage as that used in the preceding experiment (A). 

 Seven of the 12 tubes give secondary cultures. The results from five 

 other experiments with the same strains are, 9, 5, 10, 5, and 6 secondary- 

 cultures, or 70 per cent. A week later 12 cultures of the Jerv. bacillus 

 are inoculated from one of the previous tubes that had remained clear. 

 From these, 5 secondary cultures are secured. 



A further passage made after another week, gives 4 secondary cul- 

 tures in the 12 suspensions. After another week, a fourth passage, still 

 taking the bacteriophage from a perfectly hmpid culture, yields but one 

 secondary culture among the twelve inoculated. 



(C) At the beginning of convalescence in the dysentery case (Jerv.) 

 a bacteriophage was isolated which was tested in the same manner both 

 on the type Shiga strain and on the Jerv. strain. This last was derived 

 from the patient early in the infection at a time when the intestinal 

 bacteriophage had manifested no activity for this organism. 



With the bacteriophage Jerv. on the type bacillus 4 secondary cul- 

 tures develop among the 12 suspensions dissolved. 



With the bacteriophage Jerv. on the bacillus Jerv., there are no 

 secondary cultures among the 12 tubes dissolved. When repeated 

 upon an additional 12 suspensions a single secondary culture develops. 



To state the situation briefly, the frequency of secondary cultures is 

 strictly related to the virulence of the bacteriophage. With the bac- 

 teriophage of maximum virulence they do not occur when the conditions 

 are optimum for the development of the bacteriophage corpuscles. If 

 the conditions are not best suited to the development of the bacterio- 

 phage, secondary cultures may develop and the number to appear 

 becomes increasingly large as the conditions are more remote from the 

 optimum. With bacteriophage races but slightly below a maximum 

 virulence a certain number of secondary cultures can always be obtained 

 even though the conditions are optimum. A number of the bacterio- 

 phage suspensions, many or few as the case may be, will remain limpid 

 indefinitely while other tubes will give secondary cultures. With races 

 still less virulent, but yet capable of causing a total dissolution of the 

 bacteria of the suspension, secondary cultures always develop. And 

 finally, for races where the virulence is only moderate or weak, the bac- 

 teria acquire, within the first few hours, a resistance sufficient to enable 

 them to develop in spite of the presence of bacteriophage. Under such 

 conditions clearing of the medium can not take place. Coincident with 

 the dissolution of those bacteria which are least capable of developing a 



