SIZE, SHAPE, AND HYDRATION OF VIRUSES 



63 



should be certain that we are really studying the infectious unit 

 responsible for the expected symptoms and not something 

 which se})arates from highly infectious preparations and is only 

 circumstantially related to the actual infectivity. There is a 

 great deal of nonphysical evidence that crystalline, plant virus 



SBMV 



External monolayer 

 of water 



94 % protein 

 6% nucleic acid 

 Very little internal hydration 



-Monolayer 

 of hydration 



Fig. 2.13. Shape information regarding southern bean mosaic virus and 

 tobacco mosaic virus as obtained from the physical studies described in this 

 chapter. 



preparations have all the expected infective properties. These 

 are briefly summarized by Bawden in his book, where he points 

 out that the purified crystalline bodies, having recognizable 

 chemical properties which can be extracted from infected plants, 

 are never found in healthy plants. Moreover, when different 

 kinds of plants are susceptible to the same virus, the same crys- 



