42 



THE PHYSICS OF VIRUSES 



or by the rotation of one cylinder inside another with liquid 

 between. Once absolute values are established, relative values 

 can easily be found by timing the flow of a fixed volume of fluid 

 through a certain length of capillary under the action of gravity, 

 or by timing the rate of fall of a small sphere through the liquid. 

 Thus viscosity is a relatively easy measurement. 



V- 



X 



10 20 



Grams of Virus in 100 ml 



3,0 



Fig. 2.6. Plot of -q/riQ — 1, the relative viscosity less unity, for solutions of 

 SBMV of different concentrations. The circles and triangles refer to physically 

 and chemically purified virus. The slope of the line enables a determination of 

 V /m, the volume fraction of the virus, to be made. Data of Miller and Price 

 (1944). 



The Einstein equation is seen to be very powerful in the case 

 of purified spherical viruses. The number of virus particles 

 per milliliter can be measured in terms of the mass of dry virus 

 per milliliter, and the mass of the virus found by sedimentation 

 and diffusion. If C is the mass per milliliter and m is the mass 

 of each virus particle, then the number of particles per milliliter 

 is C/m. Now if the actual volume of each, water included, is F, 

 we have = CV /m, the number per milliliter times the volume 

 of each. So a measurement of 17/770 as a function of C tells us the 



