190 



THE BACTERIOPHAGE AND ITS BEHAVIOR 



solved suspension of the preceding tube. Transfers are made after 

 twenty-four hours, that is, at a time when dissolution is complete. 

 (See table 17.) 



Certain salts, when added to the suspension in very minute quantities, 

 0.1 mgm. to 10 cc. of culture, favor the development of secondary cul- 

 tures. The salts of lead (nitrate and acetate) and of silver (nitrate and 

 sulfate) act in this way. The soluble phosphates and magnesium sulfate 

 appear to be without action. With a single race of bacteriophage and a 

 given strain of bacillus the development of secondary cultures is, in 



general, more frequent when the suspension is prepared from agar cul- 

 tures several days old than when made from fresh cultures. 



At first thought it appears strange that when secondary cultures 

 develop with a race of bacteriophage of high potency, they appear in 

 some tubes and not in others. The following experiment offers an 

 explanation for this. 



Two flasks, each containing 200 cc. of a B. dysenteriae suspension 

 (250,000,000 per cubic centimeter) are inoculated with 0.04 cc. of a 

 culture of the bacteriophage (the same race as that used in the preced- 

 ing experiments). Immediately after inoculation the contents of the 



