20 



THE PHYSICS OF VIRUSES 



work of this kind is the study of tobacco mosaic virus within 

 Turkish tobacco plants by Bhick, Morgan, and Wyckoff (1950). 

 Tobacco mosaic virus is very suitable for such studies as it has 

 a characteristic long, thin ])article shape and so can be recog- 

 nized readily. It was found that in diseased cells the long, rod- 



Fig. 2.2. Electron micrograph of sonically treated tobacco mosaic virus, 

 taken by Dr. R. C. Williams, showing one fragment standing on end. The 

 hexagonal cross section is visible. Magnification 200,000. 



shaped particles grow inward from the cell wall and can com- 

 pletely fill the space between the wall and the nucleus. The 

 nucleus does not ajjpear to develop the characteristic virus 

 rods. Also, the length of rod seen in the plant cytoplasm is not 

 the short rod of 2,800 A length usually associated with the 

 infectious unit but is much longer. Since crystalline inclusion 



