SIZE, SHAPE, AND HYDRATION OF VIRUSES 



61 



The internal interference scattering expression should apply to 

 these viruses, and it has been found to hold. The results for 

 southern bean mosaic virus are shown in Fig. '2. 12, where it can 

 be seen that the first five secondary maxima are visil)le. This is a 

 very remarkable and most interesting result, for it shows that the 

 conditions for large-angle scattering are closely fulfilled. Put in 



SBMV 



Curve Slits 



A 61x8.5 mm 



B 0.61x8.5 mm 



C 0.81 X 10 mm 



40 



30 



20 10 



Scattering Angle 



10 

 (10- 



20 

 Radians) 



30 



40 



Fig. '■2.1''2. X-ray scattering of SBMV taken by Ritland, Kaesberg, and 

 Bee man (1950). Three sets of slits were u.sed. and it can be seen that five 

 sets of maxima are discernible. This means the virus is spherical to a close 

 approximation. 



simple terms: because the virus particles are not arranged in any 

 way, their perfect symmetry about the X-ray beam must be due 

 to their own simple shape, and, in fact, the only shape simple 

 enough is a sphere, and an accurate sphere to boot. The experi- 

 ments show that the viruses are spherical to one part in 50, which 

 is a remarkably accurate geometrical shape. They fully justify 

 the use of equations for spherical particles in sedimentation, 

 diffusion, and viscosity. Similar results on tobacco necrosis virus 

 and bushy stunt virus have been reported, so that one class of 



