V. FINER STRUCTURE OF VIRUS PARTICLES AND ITS SIGNIFICANCE 71 



It appears to the writer rather strange that virus-like rods are 

 generally believed to be never produced without virus, although we 

 are unable to determine whether or not adequate stimuli other than 

 a virus can give rise to the production of virus-like rods in plant 

 tissues, as we unfortunately have neither the electron microscope nor 

 ultracentrifuge. The above mentioned fact, however, that particles 

 or bodies with double refraction are produced by the addition of 

 ammonium sulphate suggests the possibility of rod formation without 

 virus. 



Yamafuji and his collaborators (56) claimed that they could pro- 

 duce tobacco-mosaic and polyhedrosis virus in plant leaves and silk- 

 worms respectively by application of such chemicals as H2O2 or 

 hydroxylamine. It is a question whether or not viruses themselves 

 were actually produced, but at least it seems certain that some che- 

 micals could cause the expulsion of lipids to form virus-like bodies or 

 aggregates. They attempted to connect oxidation process with this 

 apparent virus formation, but it should be remembered that oxidizing 

 agents, in general, exhibit profound effects upon protoplasm structure 

 and that the general mutagenic activity of peroxide in microorganisms 

 seems fairly established (57). Mutagenic activity of some agents can 

 be considered to be based upon their ability to produce a structural 

 change in nucleoproteins in protoplasm as discussed later. Therefore, 

 if some agents could raise, like viruses, certain changes in protoplasm 

 protein to break the combination of the protein with lipids, virus-like 

 rods containing no lipids would be produced. According to a more 

 recent report by Yamafuji et al. (57 a) polyhedral virus crystals formed 

 chemically in silk-worm larvae exhibit the same electrophoretic pattern 

 as those produced naturally by infection. 



It seems to be believed by a number of workers that certain plant 

 viruses, at least tobacco-mosaic viruses, are rod-shaped particles, and 

 that such rods or particles are the only feature of the viruses. How- 

 ever, the writer holds the opinion that the virus particles without 

 lipids are rather an exceptional existence even in tobacco-mosaic 

 viruses, but that like many animal viruses these plant viruses usually 

 exist in particles containing lipids. If the combination with the lipids 

 was not broken by the virus infection, elementary bodies would coa- 

 gulate in their natural state even in the plant cells and would come 

 out as virus particles. 



We failed to obtain any particles or aggregates having double re- 

 fraction from infected tomato leaves in summer even when ammonium 

 sulphate was applied, but could isolate in abundance only particles 

 containing considerable quantities of lipids as in the case of animal 

 viruses. Bawden (25) stated that the yield of plant viruses varies 



