372 GROWTH OF BACTERIOPHAGE 



formed with bacteria grown on agar to indicate that in other respects 

 their behavior is similar to that of the bacteria grown in broth. The 

 bacteria grown in this way on agar slants are in some way more sus- 

 ceptible to lysis than the broth cultured bacteria. 



A dsorption 



The first step in the growth of bacteriophage is its attachment to 

 susceptible bacteria. The rate of this attachment can be readily 

 measured by centrifuging the bacteria out of a suspension containing 

 phage, at various times, and determining the amount of phage which 

 remains unattached in the supernatant {cf. Krueger (10)).^ 



According to the picture of phage growth outlined above, phage 

 cannot multiply except when attached to bacteria; therefore, the rate 

 of attachment may, under certain conditions, limit the rate of growth. 

 We wished to determine the rate of this adsorption so that it could be 

 taken into account in the interpretation of growth experiments, or 

 eliminated if possible, as a factor influencing the growth rate. Our 

 growth curves show that there is no increase in the number of infective 

 centers up to a critical time; we could therefore, make measurements 

 of the adsorption on living bacteria suspended in broth, so long as the 

 time allowed for attachment was less than the time to the start of the 

 first burst in the growth curve. The adsorption proved to be so rapid 

 that this time interval was ample to obtain adsorption of all but a few 

 per cent of the free phage if the bacteria concentration was above 

 3 X 10^ The number of bacteria remained constant; the lag phase 

 in their growth was longer than the experimental period. 



The rate of attachment was found to be first order with respect to 

 the concentration of free phage (P/) and first order with respect to the 

 concentration of bacteria {B) over a wide range of concentrations, in 

 agreement with the results reported by Krueger (10). That is, the 

 concentration of free phage followed the equation 



- '-^ = UPf)iB) 

 at 



^ A very careful study of the adsorption of a co/z-phage has also been made 

 by Schlesinger (Schlesinger, M., Z. Hyg. u. Infektionskrankh., 1932, 114, 136, 

 149). Our results, which are less accurate and complete, agree qualitatively 

 and quantitatively with the results of his detailed studies. 



44 



