58 



THE PHYSICS OF VIRUSES 



which is the sei^aration for hexagonal rods in contact. Thus the 

 effect of removing the dryable hydration cannot well be more 

 than that produced in going from 178 A to 151 A. So extreme 

 hydration proposals are not likely to be true. Actually, the 

 values already quoted, as proposed l)y Schachman and Lauffer, 

 fit these figures quite well. 



The shrinkage of bushy stunt virus on drying reduced the 

 interparticle distance from 394 A to 318 A, and the process was 

 reversible. Thus rather higher hydration is possible. 



Small-Angle X-Ray Scattering by Viruses 



A method which promises to be very powerful has recently 

 been applied to virus study by Kratky (1948) and by Ritland, 



GM 

 Counter 



Target 

 X-ray Tube 



Ni-Co 

 Filter 



Scatterer 



Fig. 2.11. Schematic arrangement for low-angle scattering of X-rays by 

 viruses as used by Kaesberg, Ritland. and Beeman. A high-current rotating- 

 anode X-ray tube supplies a beam which is filtered and collimated before en- 

 countering the scatterer. This is a solution of virus. Scattering is measured as a 

 function of angle with the Geiger-Miiller counter. 



Kaesberg, and Beeman (1950). The apparatus used by these last 

 authors is shown schematically in Fig. 2.11. The virus solution 

 is placed in a Lucite sample holder with properly oriented, thin 

 polyethylene windows. The source of X-rays is a high-power, 

 rotating-anode tube operating at about 30 kv and 100 ma, with a 

 copper anode and a thin metal window. The X-rays are filtered 

 through a nickel-cobalt filter and accurately collimated with 



