THE BACTERIOPHAGE CORPUSCLE 77 



Let US carry the experiment farther, and see if the nature of this rela- 

 tionship may be disclosed. Take a series of 12 tubes, each containing 

 9 cc. of bouillon to which a concentrated suspension of dysentery 

 baciUi has been added to give a count of 250 million bacilli per cubic 

 centimeter. With these 12 tubes, all containing like amounts of the 

 same bacterial suspension proceed as follows : 



Tube 1. Into one of these tubes, inoculate 1 cc. of a bacteriophage 

 liquid, one very active for the dysentery bacillus. Each cubic centi- 

 meter of the tube will then contain 250 milHon bacilli and 0.1 cc. of 

 bacteriophage fluid. 



Tube 2. Into a second tube introducje 1 cc. of the contents of tube 1, 

 just prepared. This second tube will then contain, per cubic centi- 

 meter, 250 million bacilli together with the tenth part of the bacterio- 

 phage fluid transferred in the cubic centimeter of material from the first 

 tube, that is, 0.01 cc. 



Tube 3. Into a third of the 12 tubes of bacillary suspension introduce 

 1 cc. of the contents of tube 2. This tube (no. 3) will then contain, as 

 did the others, 250 million bacilli per cc, and the bacteriophage pres- 

 ent in the cubic centimeter of fluid transferred from tube 2, that is, to 

 each cc, 0.001 cc. of the bacteriophage fluid. 



Continue in this manner with eleven of the tubes of dysentery bacil- 

 lus suspension, as first prepared. Each cubic centimeter of the fluid 

 in all of these tubes will then contain 250 million bacilli per cubic 

 centimeter, but each tube of the series will contain less of the bacterio- 

 phage fluid, since each successive tube will contain but a tenth of the 

 amount in the tube preceding. We will have a series of tubes, all 

 containing both bacteria and bacteriophage; but as is indicated in 

 table 9, the bacterial content is constant; the bacteriophage content is a 

 variable. 



Immediately after preparing these successive dilutions transfer a 

 normal drop (0.05 cc.) of each of the 12 tubes to agar, either a slant or a 

 plate, taking care to distribute the drop evenly over the surface, in 

 other words, spread* it in a uniform layer. Place the 12 agar cultures 

 in the incubator at 37°C. After incubation, the following facts may be 

 noted. 



The tubes upon which the specimens removed from the dilutions 

 10~^, 10~2, and 10~^ (tubes 1, 2, and 3) were spread show no trace of 



* I shall often have occasion to speak of this operation. The word "spread" 

 implying the even distribution of the'liquid over all of the surface of the agar 

 slant or the media of the Petri dish, will be employed. 



