116 THE BACTERIOPHAGE AND ITS BEHAVIOR 



The course of tmdli'plication 



The experiment described in the second section of this chapter 

 shows that: 



After 30 minutes of contact at 37°C. the bacteriophage corpuscles 

 have almost entirely disappeared from the liquid. 



After 60 minutes the situation is the same. 



After 90 minutes the corpuscles have suddenly reappeared in the 

 liquid, and their number is 18 times greater than was that of the inocu- 

 lated corpuscles. In other words, each inoculated corpuscle has yielded 

 18. 



Another experiment may be inserted, likewise showing the sudden 

 multiplication of the bacteriophage corpuscles. Six tubes of Shiga 

 bacillus suspension are inoculated with a bacteriophage suspension 

 (containing 3000 million per cubic centimeter) in such a way that 

 each tube receives one six-millionth of a cubic centimeter. When 

 incubated, four give normal cultures of B. dysenteriae and all subcul- 

 tures on agar yield normal growths. These are, therefore, without 

 interest for us. The other two, each of which received probably one, 

 certainly not more than two corpuscles, show the following picture: 

 The suspensions become more and more turbid. After 2 hours at 

 37°C. the opacity is about 2 times as great as at the beginning. After 

 3 hours it is about 2^ times as great, and after 4 hours, about 3 times. 

 It then begins to diminish, so that after 5 hours the density is about 

 twice as great as at the beginning of the incubation. This clearing 

 continues gradually, so that after 14 hours the culture is almost en- 

 tirely clear. If immediately after the inoculation with the bacterio- 

 phage, and then every 30 minutes, 0.02 cc. of each of these two sus- 

 pensions is transferred to agar slants, these tubes will show, after 

 incubation, the following: 



Plantings after 30 minutes, 1, 1^, and 2 hours yield normal growths 

 of B. dysenteriae. After 2^ hours the subcultures show 3 plaques in 

 one tube and 5 in the other (average, 4). Therefore, after 2^ hours 

 the inoculated suspension contains 2000 bacteriophage corpuscles. 



After 3 hours the subcultures show 5 and 4 respectively. There 

 has been no material increase between 2^ and 3 hours. 



The 3 J hour plantings show 9 and 5 plaques (average, 7) . The num- 

 ber of bacteriophagous elements has slightly increased. 



After 4 hours, the agar tubes show 101 and 111 plaques respectively 

 (average, 106). After 4 hours, therefore, the number of corpuscles 

 is between 50 and 60 thousand. 



