M. DELBRUCK 



653 



203— 



o 

 o 

 \ 



Ul 



=5' 



a 

 < 



IOC 



DATE 

 A 9-28 

 X 10-2 



D 10 -25 



10- 

 |L-x- 



X 



A 



X A ' 



XD 



D a 



XX 



10 20 



TIM E 



N MINUTES 



30 



40 



50 



Fig. 4. One step growth curve of phage on rapidly dividing bacteria at 37°. Direct 



plot. 



At time zero about 10^ phage/cc. were added to 25 cc. of a rapidly growing broth 

 culture of bacteria, that had been aerated for 3 hours and contained about 5 X 10^ 

 bacteria/cc. After 5 minutes, 10^-, 10^-, and 10^-fold dilutions of this growth mixture 

 were made in broth of 37° and these were further aerated and incubated. At 1 or 2 

 minute intervals samples from these mixtures were plated for plaque counts. 



It is seen that the plaque count stays constant for 17 minutes, then increases linearly 

 with time till 33 minutes when it reaches 170 times the original value. After 33 minutes 

 it stays nearly constant. Phage liberation takes place uniformly during 16 minutes. 



It should be noted that on a logarithmic plot the rise would appear to be much more 

 sudden. In fact on such a plot more than half of the step would be accomplished within 

 3 minutes, when the plaque count has risen to twenty times the original value. 



TABLE III 



Characteristics of Phage Growth on Rapidly Dividing Bacteria and on 24 Hour Aerated 

 Bacteria, Both Measured in Broth at 37° C, with Aeration 



Rapidly dividing bacteria . 

 24 hrs. aerated bacteria . . 



Minimum 

 latent period 



17 

 30 



Spread of 

 latent period 



16 



22 



Step size 



170 



20 



Saturation 

 value 



250 

 20 



would have been qualitatively the same but quantitatively quite different 

 (see Fig. 5). Table III lists the respective values. 

 The constant rate of phage Hberation in the best one step growth curves 



67 



