ADSORPTION OF PHAGE TO HOST CELL 139 



decreases as an exponential function of time until about 95 per 

 cent of the phage is adsorbed. The adsorption rate then de- 

 creases and, when killed bacteria are used, an unadsorbed 

 residue is obtained amounting lo 10~^ of the initial phage popu- 

 lation. This unadsorbed fraction does not adsorb if additional 

 heat-killed bacteria are added, indicating that failure of adsorp- 

 tion is not due to saturation of bacterial receptors, nor to a re- 

 versible equilibrium. The unadsorbed fraction adsorbs slowly 

 to living bacteria. 



After adsorption of 90 to 99 per cent of the phage to heat- 

 killed bacteria, the residual phage was titrated before and after 

 removal of the bacteria by centrifugation. The plaque counts 

 are the same in either case, indicating that adsorption is essen- 

 tially irreversible. However, after prolonged periods of adsorp- 

 tion it is found that a small fraction (10~^) of the phage popula- 

 tion can be eluted by washing. The phage population therefore 

 consists of three kinds of phage particles: those that adsorb 

 irreversibly, those that adsorb reversibly, and those that do not 

 adsorb at all to heat-killed bacteria. 



In his next paper Schlesinger (1932b) demonstrated that the 

 adsorption of at least 95 per cent of the phage population obeys 

 the kinetics described by equations (1) and (2) above. The 

 observed velocity constant k is independent of B, P, and t over 

 ranges of B from 3 X 10*^ per ml. to 7 X 10^ per ml., of Pq from 

 6 X 10^ per ml. to 6 X 10^ per ml., and of ^from 2 minutes to 

 12 hours. The adsorption rate on living bacteria is 2.6 times 

 faster than on heat-killed bacteria. Schlesinger interpreted this 

 difference as being due to destruction of somewhat more than 

 half of the receptor sites during the heat-killing of the bacterial 

 culture. 



Schlesinger determined the adsorption capacity of heat-killed 

 bacteria for phage by increasing the phage to bacterium ratio to 

 several hundred. The maximum adsorption capacity is 140 

 phage particles per bacterium. If Schlesinger's explanation for 

 the reduced adsorption rate is correct, the adsorption capacity 

 of living bacteria might be 140 X 2.6 or 360 phage per bac- 



