54 THE BACTERIOPHAGE AND ITS BEHAVIOR 



A suspension of 250 million of bacilli per cubic centimeter is inocu- 

 lated with 0.0001 cc. of a bacteriophage filtrate. After 14 hours the 

 dissolution of the bacteria is complete, the medium being clear. At this 

 time, a concentrated suspension of young bacilH is added to this clear 

 medium in such a way as to restore the titre to 250 million per cubic 

 centimeter. Seven hours later the medium is again limpid, all of the 

 bacteria having been dissolved. Another addition of a new quantity 

 of concentrated suspension is made, again yielding a turbidity cor- 

 responding to 250 million bacteria to each cubic centimeter. This 

 time, after 48 hours, the medium is still sHghtly cloudy. 



To this medium, not entirely clear, a further addition of concentrated 

 bacterial suspension is made, restoring the turbidity to the equivalent 

 of 250 milhon bacteria per cubic centimeter. Eight days later the 

 medium has cleared somewhat, but it is still definitely cloudy. How- 

 ever, plantings made from it upon agar and into bouillon remain 

 sterile. 



As is seen, whether the bacteria were present in the medium from 

 the beginning, or whether they were introduced by fractions in the 

 course of the action, the dissolution was complete only for quantities 

 below approximately 700 millions per cubic centimeter of medium. 

 Later we will have more to say about the cause which operates to 

 hinder dissolution of more than a certain number of bacteria per unit 

 volume of fluid. 



These experiments reveal the fact that the bacteriophage principle 

 is able to effect a complete dissolution of the bacterial cells in suspen- 

 sion in a medium propitious for bacteriophagy when the medium con- 

 tains from one to 700 million bacterial cells per cubic centimeter. 

 Within certain very wide hmits the quantity of bacteriophage filtrate 

 necessary to inoculate to cause this dissolution is a matter of no moment; 

 the course of the action and the final result of the phenomenon is the 

 same, whether the amount inoculated is 1 cc. or 0.001, to 10 cc. of 

 medium. 



The total number of bacteria which may undergo a complete dis- 

 solution under the action of a very active bacteriophage appears 

 to vary with different species of bacteria. As has been seen above, 

 the maximum is about 700 milUon for B. dysenteriae, whether it be 

 Shiga, Flexner, or Hiss, and for the staphylococcus, whether it be albus, 

 aureus, or citreus. With B. coli, B. typhosus, and B. paratyphosus A 

 and B, a complete dissolution has been obtained with quantities of 

 350 million per cubic centimeter of medium but not of higher concen- 



