70 II. FUNDAMENTAL STRUCTURE OF PROTOPLASM 



rization increasing as the latter increases. Insulin was also thought 

 as a reversibly dissociable system, its unit molecular weight being 

 believed to be 6,000 (54). 



An interesting fact was found with insect viruses that the viruses 

 are isolated not only in the form of rod-shaped particles as above 

 described but also in much thicker rods each of which appears to be 

 composed of a number of the usual rods fusing together in parallel align- 

 ment. For example, in the case of polyhedrosis of the gypsy-moth 

 caterpillar such extremely thick rods as 160x415 m/<. were found in 

 addition to the usual rods of 41x360 m/i. In the case of nun-moth 

 caterpillar most particles were proved so thick as appearing almost 

 globular (34). Such a thick globular rod may be interpreted as the 

 elementary body itself from which only lipids have been eliminated. 

 The thinner usual rods or needles should be regarded as produced on 

 the dissociation of such thick rods. 



These thick rods have proved in general to be much longer than 

 the usual thin rods or needles, a fact which may depend upon lesser 

 degrees of the shrinkage due to the desiccation owing to their great 

 thickness. Williams and Steere (55) have found in electron micro- 

 graphs that also tobacco-mosaic virus particles exist in forming thick 

 bundles in the juices from infected tobacco leaves ; if the specimens 

 are washed with one or two drops of distilled water before drying 

 and shadowing with uranium, the bundles disintergrate into single 

 needles. 



2. Virus Particles Containing Lipids 



As above discussed, some plant virus particles or rods can be 

 regarded as elementary bundles whose structure has been altered by 

 a virus and from which subsequently lipids have been expelled. The 

 formation of similar particles may not be impossible if adequate physi- 

 cal or chemical effects other than viruses, which may be able to cause 

 some disturbances in the protoplasm structure to expel the lipids, 

 are applied to the protoplasm. 



It is, however, generally believed that no virus-like rods can be 

 isolated from normal plant tissues. Nevertheless, according to our in- 

 vestigation as shown already minute particles with double refraction 

 could be obtained from various normal plant materials when the saps 

 were treated with ammonium sulphate. It was uncertain whether or 

 not such particles having double refraction were aggregates of the rods, 

 but there seemed no doubt that the lipids could be expelled by the 

 action of ammonium sulphate, since the particles contained no lipids. 



