THE MECHANISM OF BACTERIOPHAGY 



127 



suspension was originally prepared and divided into two equal por- 

 tions, one part being used in the test presented above) with 500 

 milHon corpuscles. After 3 days (bacteriophagy was complete in 

 less than 24 hours) the number of corpuscles was 7000 million. 



Cause of the arrest of multiplication 



It may be asked why the bacteriophage ceases to multiply when the 

 medium contains a certain number of them, even though bacteria are 

 still present. Quite as logically it might be asked why bacteria stop 

 multiplying even though food materials are left in the medium. The 



answer is the same in both cases. Multiplication stops when the prod- 

 ucts resulting from the "vital reaction" reach a certain concentration. 



Insofar as bacteriophagy is concerned, let us note first that with all 

 of the conditions best suited to bacteriophagy the final number of 

 corpuscles differs with the bacterium attacked. With the most active 

 races of the Shiga-bacteriophage I have never obtained a final titre 

 greater than about 10,000 million per cubic centimeter. With the 

 Staphylo-bacteriophage the final titre often goes above 100,000 milhon. 



In the first chapter the statement was made that the substances 

 resulting from the distinctive activity of the bacterium, that is, those 

 substances which "vaccinate" the medium against the bacterium, 

 do not exert an inhibitory effect upon bacteriophagy. The experi- 

 ments carried out with Shiga baciUi leading to this conclusion-^ ^ have 

 been confirmed by Maitland.^^^ 



