62 



S. BENZER 



[vol. 63 



(Dulbecco, 1950). However, the absence of phage hberation is not sufficient to 

 exclude the possibihty that intracellular growth progresses to a fairly advanced 

 intermediate stage without reaching completion. 



We can test for this by making use of the large change in resistance to ultra- 

 violet of T2r complexes. If intracellular development proceeds, the resistance 

 should increase with time. In figure 2, it can be seen that so long as the infected 

 cells are kept in buffer and no nutrient is added, the resistance remains constant. 

 The value of the resistance is only slightly higher than that of the free phage 



f— in broth ot 37' 



T2I 



f 



buffer ot 37 



50 



60 



10 20 30 40 



TIME IN MINUTES 

 Figure 2. Effect of addition of nutrient upon the radiation resistance of T2r complexes 

 formed in buffer. The ordinate is obtained by exposing a sample of complexes to ultraviolet 

 for 55 seconds and determining the fraction which survives. (A) No nutrient added; (B) 

 broth added at time zero. 



(see later). Thus, the intracellular development does not progress beyond a 

 very early stage. Even if the adsorption period extends over many minutes, 

 each complex is arrested in its development, and adsorption is effectively simul- 

 taneous. 



In experiments with bacteria grown in synthetic medium (instead of broth) there was a 

 slow increase of resistance, even in buffer, as if considerable intracellular nutrient reserves 

 remained even after starving for an hour. This resistance reached a maximum value corre- 

 sponding to that attained after several minutes of growth in the presence of ample extra- 

 cellular nutrient. 



301 



