THE SURFACE OF VIRUSES 125 



The values of k-z so measured are of the order of 5 X 10""^^ cm^/ 

 sec. Krueger (1931) showed that adsorption to live and dead 

 bacteria followed the above relation and measured ki for 

 staphylococcus phage. Schlesinger (1932) pointed out that if 

 the collision rate expected from Brownian movement of the 

 bacterium and the virus were the only agent responsible for this 

 rate, the value of A-o calculated is about what is found. Delbriick 

 (1940) assumes that because the virus is removed by adsorption 

 near the surface of a spherical bacterium, radius o, there exists 

 a concentration function C{r), where 



C{r) = C. (l - f) 



where r is the distance from the center of the bacterium, and C«, 

 is the concentration at infinite distance, i.e., the average con- 

 centration. There will then be a rate of flow, F, on to the 

 bacterium given by the concentration gradient, dC/ dr, times 

 the area, 47r/--, times the diffusion constant, D, so that 



F = 47r/-2 V = C^^irDa 

 dr 



Since F = k^^X^^, we have k„,^^ = AiTr Da, where k„^^ is the 

 maximal attachment constant. 



The fact that k^ is so close to this figure argues that attach- 

 ment occurs every time, that it does not depend on the orienta- 

 tion of the virus, and so that the whole virus surface, or at least 

 an equally distributed pattern of small units, is involved in this 

 attachment. Alternatively, an attraction of a specific charge 

 must occur. 



A great clarification of the nature of this process resulted from 

 the very direct experiments of Puck, Garen, and Cline (1951). 

 In studying values of /r2 by the method outlined above, they 

 found that although T-1 and T-3 phages fitted the rapid adsorp- 

 tion pattern, T-2 and T-4 did not until NaCl was added. This 

 feature of virus attachment had been discovered by Hershey 

 (1946). Cherry and Watson (1949) observed that the lysis of 

 Streptococcus lactis by a phage in the presence of MgSOi showed 



