120 II. FUNDAMENTAL STRUCTURE OF PROTOPLASM 



length of a globulin molecule stretching in its polypeptide chain. 



Such lipid-free particles, however, do not represent the only 

 feature of the plant viruses, but they may rather be a peculiar feature. 

 Thus, also in plant viruses coagulated elementary bodies themselves 

 can be recognized as the most common virus particles as in animal 

 viruses. In addition, also the elimination of lipid itself is by no- 

 means peculiar to plant viruses ; various polyhedrosis viruses of 

 insects are isolated in lipid-free, needle-shaped particles similar to 

 certain plant viruses both in shape and length. 



Ammonium sulphate can sometimes expel the lipid from the plant 

 protoplasm, so that crystals like those of some viruses are occasionally 

 obtained from normal plant saps by treating with the salt. 



In healthy plant cells the combination between the protein and 

 lipid appears to be so firm that lipid elimination fails to occur of 

 itself without the action of a certain virus, and consequently the 

 lipid-free needles are customarily believed as the only feature of the 

 virus. It seems possible, however, to produce virus-like lipid-free 

 particles in plant or insect tissues by the application of some proper 

 agents other than viruses. 



The action of viruses may arise from the pattern of the protein 

 molecules constituting the particles, and the effect of the pattern may- 

 be strengthened by the polymerization of the protein. Lipids are not 

 necessary for the virus action, but indispensable for the protoplasm to- 

 freely change in its configuration when infected by a virus. Owing to 

 the lipids, proteins can change their structure in the protoplasm, the 

 change being transmitted throughout the cell, thereby the structure 

 specific to a virus is given rise to. The free motions of protein mole- 

 cules in the protoplasm owing to the presence of lipids must be the- 

 essential picture of the life itself. 



The bundles of protoplasm-protein threads appear to have the 

 property to associate end-to-end to form unusually long filaments. As 

 a consequence certain plant viruses may occasionally reveal them- 

 selves in long filaments. At the same time, the bundle tends to split 

 into shorter fragments, being accompanied, as a rule, by either a loss 

 or decrease in the virus activity. It seems probable, however, that 

 some plant virus proteins are so brittle that they can split into ex- 

 tremely small fragments without great disturbance in their structure 

 and consequently without loss of its activity. In such a case, viruses 

 can be obtained in extremely small particles. A number of plant 



