646 



GROWTH OF PHAGE AND LYSIS 



10 r— 



o AERATED 

 xNOT AERATED 



3 4 



TIME IN HOURS 



Fig. 1. Growth of bacteria in broth at 37°. 



The inoculating bacteria were taken from an 18 hour not aerated broth culture. 

 Without aeration the growth reaches saturation at 10* B/cc. With aeration the growth 

 proceeds further beyond 10^ B/cc. The maximum growth rate is in both cases equal 

 and corresponds to an average division time of 30 minutes. The cessation of growth 

 in the unaerated culture is therefore caused by lack of air. This is further supported 

 by the top curve, which shows how the unaerated 18 hour culture, without the addition 

 of fresh broth, proceeds to grow, when aerated, and reaches about 2 X 10^ B/cc. 



Fig. 2. Growth of the standard experimental culture of bacteria in broth at 37°. 



At time zero 0.1 cc. of a 24 hour stock culture was added to 25 cc. broth. Every 

 7.5 minutes platings were made for colony counts. The plotted values show complete 

 agreement with Hershey's (11) finding that such aerated bacteria exhibit a sudden 

 transition from the phase of cell enlargement (lag period) to the phase of cell division. 

 The lag period is 2 hours, if defined as the time required for increase in cell number by a 

 factor 1.5 (compare Hershey's discussion (11)). 



60 



