THE MECHANISM OF BACTERIOPHAGY 



111 



sterilized, is placed, in such a way that migration through the material and the 

 fluid is rendered very difficult. These tubes are then filled with bouillon to a 

 height of 3 or 4 cm. above the sand. (They may be used for several purposes, 

 particularly for separating B. typhosus from B. coli.) 



In an apparatus of this type (no. 1*) we inoculated a drop of a virulent bac- 

 teriophage suspension (strain H of d'Herelle) in the first vertical arm. Tests 

 were made after 2, 4, 6, 8, 12, and 24 hours to see if the bacteriophage had pene- 

 trated to the other vertical arms. These tests consisted simply in seeding a 

 loopful of the contents of each arm on to agar previously implanted with Shiga 

 bacilli. These agar cultures were allowed to incubate for 24 hours, and then the 

 number of plaques, that is, the number of bacteriophage corpuscles appearing 

 were recorded (see the table). When the plaques were completely fused together, 

 resulting in a large sterile area covering the entire surface of the medium the 

 result was expressed as infinity (o°). 



In another apparatus (no. 2), under the same conditions, we inoculated the 

 bacteriophage into the first upright arm after this had been filled with bouillon 

 seeded with Shiga bacilli. In a third apparatus (no. 3) the bacteriophage was 

 inoculated into pure bouillon in the first arm, and the last, or seventh, we im- 

 planted with Shiga bacilli. In a fourth apparatus (no. 4) only Shiga bacilli were 

 implanted; this set to test (as a control) the rapidity with which bacterial infil- 

 tration into the neighboring arms occurred. This control showed that after 4 

 hours the bacilli were to be found in the second arm only. Obviously, the abso- 

 lute rate of penetration of bacilli and bacteriophage depends, ceteris paribus, 

 upon the size of the grains of sand. 



The results of these tests are summarized as follows: 



See the table below. 



