VIRUSES 



FIGURE 5 - ELECTRON MICROGRAPH OP TOBACCO MOSAIC 

 VIRUS PARTICLES. (W. IL. Stanley and T. P. Anderson, 

 J. Biol. Chem. I39, 325 (1941) ). 



It can 'be seen that they actually are rod-like bodies with a thickness of 15 mu 

 and a length of 270 mu, approximately the dimensions predicted from indirect 

 studies . 



Earlier it was mentioned that sometimes tobacco mosaic virus mutates to 

 form new strains which cause new diseases. The resultant virus nucleoproteins 

 are slightly different from that of ordinary tobacco mosaic virus. This can be 

 illustrated by the case of a particularly interesting strain of tobacco mosaic 

 virus which in nature causes a disease of ribgrass. This virus produces a 

 disease in tobacoo plants which, in its later stsigea, looks a bit like tobacco 

 mosaic. Two stages are illustrated in Figure 6. 



