376 



GROWTH OF BACTERIOPHAGE 



to minimize reinfection during the period of observation. This is 

 obtained by diluting the phage-bacteria mixture (after initial contact 

 to secure adsorption) to such an extent that the rate of adsorption 

 then becomes extremely small. In this way, a single "cycle" of growth, 

 (infection, growth, burst) was obtained as the following example 



Min, 



Time 



Fig. 3. One-step growth curves. 

 A suitable dilution of phage was mixed with a suspension of bacteria con- 

 taining 2 X 10* organisms per cc. and allowed to stand at the indicated tempera- 

 ture for 10 minutes to obtain more than 90 per cent adsorption of the phage. 

 This mixture was then diluted 1 : 10^ in broth, and incubated. It was again diluted 

 1 : 10 at the start of the first rise to further decrease the rate of adsorption of the 

 phage set free in the first step. The time scales are in the ratio 1:2:6 for the 

 temperatures 37, 25, and 16.6°C. Log P/Pq is plotted, Po being the initial con- 

 centration of infective centers and P the concentration at time t. The broken 

 line indicates the growth curve of the bacteria under the corresponding conditions. 



48 



