THE BACTERIOPHAGE AND THE BACTERIUM 



75 



Experiment XXI. This experiment shows the serial activity of the bac- 

 teriophage together with the appearance of secondary cultures. Each 

 tube of the series is prepared with a suspension of B. dysenteriae, 250,000,000 

 per cubic centimeter, and into each is introduced 0.001 cc. of the lysed 

 suspension of the preceding tube. Transfers are made after twenty-four 

 hours, that is, at a time when lysis is complete. 



A FRESH SUSPENSION RECEIVED THE 

 MATERIAL INDICATED 



July 8 

 July 9 

 July 10 



July 11 

 July 12 

 July 13 

 July 14 



July 15 

 July 16 

 July 17 



0.001 cc. of bacteriophage culture 

 0.001 cc. of suspension lysed on July 8 

 0.001 cc. of suspension lysed on July 9 



0.001 cc. of suspension lysed on July 10 

 0.001 cc. of suspension lysed on July 11 

 0.001 cc. of suspension lysed on July 12 

 0. 001 cc. of suspension lysed on July 13 



0.001 cc. of suspension lysed on July 14 

 0. 001 cc. of suspension lysed on July 15 

 0. 001 cc. of suspension lysed on July 16 



Permanent lysis 

 Permanent lysis 

 Secondary cultures in 3 



days 



Permanent lysis 

 Permanent lysis 

 Permanent lysis 

 Secondary cultures in 4 



days 



Permanent lysis 

 Permanent lysis 

 Permanent lysis 



Certain salts, when added to the suspension in very minute 

 quantities, 0.1 mgm. to 10 cc. of culture, favor the development of 

 secondary cultures. The salts of lead (nitrate and acetate) and 

 of silver (nitrate and sulfate) act in this way. The soluble phos- 

 phates and magnesium sulfate appear to be without action. 

 With a single strain of bacteriophage and a given strain of bacil- 

 lus the development of secondary cultures is, in general, more 

 frequent when the suspension is prepared from agar cultures 

 several days old than when made from fresh cultures. 



At first thought it appears strange that when secondary cultures 

 develop with a strain of bacteriophage of high potency, they ap- 

 pear in some tubes and not in others. The following experiment 

 offers an explanation for this. 



Experiment XXII. Two flasks, each containing 200 cc. of a B. dysenter- 

 iae suspension (250,000,000 per cubic centimeter) are inoculated with 0.04 

 cc. of a culture of the bacteriophage (the same strain as that used in the 

 preceding experiments). Immediately after inoculation the contents of 

 the first flask is distributed into 20 tubes, 10 cc. to each. In all of these 

 lysis takes place normally, being permanent in 19, showing a secondary 



