M. Schlesinger 



phage of 100 m/x. On the other hand, utihzmg k for killed bacteria (1.3 X 10~ "), 

 one calculates a particle diameter of 260 m/x. This latter value is undoubtedly 

 too high; thus, in the case of heat-killed bacteria, it seems certain that not every 

 collision can lead to fixation. It follows from this calculation that the adsorption 

 velocity of the bacteriophage is not too great to be fully explained by Brownian 

 movement alone. If one reverses this calculation and estimates the adsorption 

 velocity constant from the known particle size of the bacteriophage (80 to 90 m/x; 

 see below), one obtains a value of approximately 4 X 10~'^ It seems probable 

 that this agreement in order of magnitude of different, independent estimates of 

 the particle diameter can be taken as confirmation of the essential validity of 

 the concepts on which these estimates were based. 



b) Calculation of the Particle Size from the Saturation Capacity. The particle 

 size of the bacteriophage can be calculated from the saturation capacity, if it is 

 assumed that the bacterial cell absorbs that maximum number of phages which 

 can completely cover its surface with a monolayer of particles. The premise that 

 the adsorption takes place in a single layer, i.e., that it results only from direct 

 contact between phage and bacteria, is justified on the basis of the irreversible 

 and specific nature of the adsorption process^. On the other hand, the assumption* 

 that saturation occurs only after the entire surface of the bacterium has been 

 covered by phages is inherent in the previous hypothesis that every contact 

 between phage and bacterium leads to fixation. For every contact can lead to 

 fixation only if the entire bacterial surface is capable of phage fixation^. 



In case of close-packing, 140 spheres of diameter 8 cover a surface of 140 5^ 

 If this value is equal to the surface of the bacterial cell, that is to say 2.3 M^ then 

 it follows that 5 = 127 m/x- If one considers, however, that random collisions of 

 phage particles will hardly cover the bacterial surface in the closest packing 

 assumed here, and that the number 140 refers to the adsorption capacity of 



''In the case of heat-killed bacteria, there can be no question of any penetration of the 

 bacteriophage into the interior of the cell; at least there is no indication of such a possibility. 



^Obviously, this hypothesis refers to conditions under which there can be no question of any 

 interference with adsorption by partial saturation; that is to say, under conditions of great 

 excess of bacteria. The assumption that this hypothesis is not fully applicable to heat-killed 

 bacteria will be considered below. 



^However, even if the entire surface of the bacterium were capable of phage fixation, it would 

 not necessarily follow that every collision would lead to fixation ; other prerequisites of fixation 

 might be appropriate direction and adequate intensity of the collision. In the event that only 

 a number of isolated points, instead of the entire surface, is capable of fixation, then only those 

 collisions which bring the phages into contact with these "valence points" could lead to fixation. 

 The saturation capacity (S) then represents the number of such points. This assumption also 

 makes possible an estimate of the phage diameter 5, on the basis of the equation 



This equation states that the adsorption velocity is proportional to the fraction of the bacterial 

 surface capable of adsorbing the phage. The calculation, for which k for heat-killed bacteria 

 must be employed since S refers to the adsorption capacity of heat-killed bacteria, leads to a 

 value of 5 = 19 nxfi. If we assume the correctness of our direct determination of particle size 

 of the phage (80-90 m^i) mentioned below, then this low estimate of the phage diameter indicates 

 that almost the entire bacterial surface must be covered by "valence points." 



34 



