THE SIZE AND SHAPE OF VIRUSES 



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1,02 104 r06 108 



SOLVENT DENSITY 



FIGURE 24 - SEDIHEITTATIOIJ RATE VERSUS SOLVENT DENSITY 

 FOR PR 8 INFLUENZA A VIRUS IN SERUTi ALBUMIN SOLUTIONS. 

 (D.G. Sharp, et al. Science 100, l^l (1944) }. 



Here sedimentation rate of influenza virus is plotted against solvent density. 

 This time the data fall on a straight line. They indicate that in a solvent 

 of density 1.10 the virus would not sediment. Therefore, the hydrated density 

 of Influenza virus is 1.10. This result is accurate to at least one decimal 

 place more than the one obtained from the study using sugar solutions. It 

 clinches the argument that influenza virus contains an appreciable amount of 

 water when it is suspended in an aqueous medium. From the sedimentation con- 

 stant and the wet density of 1.10, it is possible to calculate that the diameter 

 of the wet influenza particle is 114 mu . Also, from the wet density, the dry 

 density, and the density of water, it is possible to calculate that the wet in- 

 fluenza virus particle contains 60^ by weight of water. 



There are several general conclusions that can be drawn from these studies 

 on the size and shape of viruses. First of all, viruses, particularly tobacco 

 mosaic virus, provided a remarkable tool for investigation for the first time of 

 the validity of theoretical equations derived from hydrodynamic considerations 

 relative to the size and shape of suspended particles. Thus, the study of 

 viruses has contributed to the advancement of physics and physical chemistry. 

 Second, many viruses contain water in their make-up. The measurement of the 

 amount of water associated with the viruses represents the first unambiguous 

 determination of the water of hydration of any protein in solution. Third, in- 

 fluenza virus was demonstrated not to be strictly uniform in size. Thus, this 

 virus does not satisfy the criterion demanded of molecules. In general, most 

 viruses causing diseases of animals and man thus far studied seem to resemble 

 Influenza virus more than plant viruses. 



