CHAPTER IV 

 THE CRYSTALLINITY OF VIRUSES 



1. The Fusion of Particles 



Virus-like particles can be isolated also from healthy plants by 

 the same procedure by which the particles are isolated from animal 

 tissues. We carried out experiments with plant materials such as leaves 

 of cucumber (jCiicumis sativus, L.). kidney-bean plant {Phaseolus vul- 

 garis, L.), tomato plant {Solanum lycopersicum, L.), poplar (Pophdus 

 nigra, L.), spindle-tree {Evonynus japonicus. Thumb.), dandelion {Ta- 

 raxacum Melongena, L.) and petals of flowers of bindweed (Catystegia 

 subvolubilis, Don.) (24). 



Virus-like particles were recovered without exception from all these 

 normal plant materials. In the case of tomato plant, we used leaves 

 infected with mosaic virus as well as healthy ones, and were able to 

 isolate similar particles from both materials. Berkefeld-filtrates of these 

 plant saps diluted with water were added with acetic acid and precipi- 

 tates produced thereby were separated by means of ordinary centrifuge. 

 In the majority of cases the optimum precipitating point was found at 

 a more acid side than in the case of animal materials, and particles 

 obtained were proved to be usually smaller than those of animals. 



Plant particles thus obtained shared a peculiar property not present 

 in particles of either animal or bacterial origin, and tended to aggre- 

 gate into larger particles or bodies. For example, particles of dande- 

 lion did form coccoid bodies of about 3/z in diameter when left at pH 

 4.0 for several days, and particles of cucumber aggregated to bacillary 

 bodies which sometimes further developed into large homogeneous pro- 

 tozoa-like bodies. It is a noteworthy fact that in such bodies original 

 particles entirely disappeared, but on the addition of dilute alkali, the 

 particles would reappear and occasionally the homogeneous bodies would 

 be broken down into the particles. 



The fusion of particles into such larger masses was never observed 

 with animal or bacterial particles. Some of such large masses would 

 appear as if they were crystals, but no double refraction was demon- 

 strated. Occasionally uniform large bodies were formed immediately 

 after the precipitation of particles by acetic acid ; in such cases it could 

 be clearly seen under the microscope by dark field illumination that 

 they were composed of minute particles which, however, when allowed 



