THE MECHANISM OF BACTERIOPHAGY 105 



b. Counts on the suspension after incubation for 30 minutes are 3, 

 7, 4, 6, 6, and 3 plaques. The average is 5. This indicates that there 

 are 125,000 bacteriophagous corpuscles in the suspension 30 minutes 

 after the inoculation. That is, of each 41 corpuscles inoculated, 40 

 have disappeared from the fluid. 



A count made directly upon the suspension, without centrifugation, 

 gives 5,000,000 elements per cubic centimeter. It is therefore certain 

 that the corpuscles which have disappeared from the fluid during the 

 centrifugation have gone down with the bacteria. And, as we will 

 see in the two control experiments, in the absence of Shiga bacilli 

 this sedimentation of the bacteriophage does not occur (at least, when 

 centrif uged at a speed of 4000 revolutions) . 



c. After 1 hour, the count, made as before upon the supernatant 

 fluid gives an average of 8 plaques, or 200,000 corpuscles per cubic 

 centimeter; a number essentially the same as that secured after 30 

 minutes. At this time a count of a suspension which has not been 

 centrifuged gives 6,500,000; a number very close to that secured im- 

 mediately after the inoculation. 



d. Counts made upon the suspension with and without centrifu- 

 gation after one and one-quarter hours give the same number of cor- 

 puscles — about 90 million. The inoculated corpuscles have therefore 

 increased from 5 to 90 millions; the increase being in a proportion of 

 about 1:18. And this increase has taken place in apparently a very 

 abrupt manner, only to be explained as a result of the liberation of 

 actual colonies containing an average of about 18 corpuscles. We 

 will see by ultramicroscopic examination that the dissolution of a para- 

 sitized bacterium takes place brusquely, by bursting. 



Tube 2. Control. Suspension of V. cholerae plus the Shiga-bacterio- 

 phage. 



Counts made immediately after inoculation of the bacteriophage 

 give; for the centrifuged material, 201; for the non-centrifuged, 211 

 plaques. 



After 30 minutes the counts are: for the centrifuged, 210; for the 

 non-centrifuged, 216. 



After 1 hour the counts are: for the centrifuged, 203; for the non- 

 centrifuged, 199. 



After one and one-haK hours the non-centrifuged suspension gives 

 207. 



Tube 3. Control. Sterile bouillon plus Shiga-bacteriophage. 



The counts immediately after the inoculation are: for the centri- 

 fuged, 206; for the non-centrifuged, 210. 



