6 I. INTRODUCTION TO VIRUSES 



been changed into such particles and isolated as such. According to 

 our experiment, for example, phage particles weighing about lxl0~''r 

 in the dry state were obtained per cell of E. colt, whereas the dry- 

 weight of a single cell was estimated to be l.lXlO~''r (9). Since the 

 ■dry weight of a single coli-phage particle obtained by us was measured 

 to be about 1 X 10"^ r, some 10' particles would be produced from a single 

 bacterial cell, if its whole protoplasm was changed into phage particles. 

 On the other hand, Delbriick estimated the number of phage particles 

 produced from a single cell to be 100 to 300, and designated as "burst 

 size" (10); this figure seems to be in accord with our estimation. 

 Likewise in the case of vaccinia virus, from the infected skin tissue of 

 a rabbit or of a calf are obtained amounts of particles so large that 

 the whole protoplasm of the tissue seems to have been converted into 

 the particles. In addition, it can actually be observed under the micro- 

 scope by the dark field illumination that the cells are fully packed with 

 virus-like particles (11). 



From these facts we have concluded that the protoplasm has the 

 property to be readily changed into minute particles by physical or 

 chemical effects and that when produced by a virus the particles are 

 endowed with the virus activity. Our theory of the virus was based 

 on the fact above stated that virus-like particles can be obtained from 

 the normal cells, but most workers seemed to pay little attention to 

 this important fact when it was first found by us. In recent years, 

 however, this became generally accepted and at present particles are 

 called "normal components" or "healthy particles" (12), although no 

 workers seem as yet to value this fact so high as we do. 



When the normal particles were first recoginzed, the writer expressed 

 the opinion that the relationship between the particles and the virus 

 might be comparable to that between serum globulins and the antibody. 

 This belief has become at present still much firmer to the writer ; the 

 reason will be made clear by degrees with the progress of the 

 description. 



3. Virus Particles as Denaturase 



Under the microscope by dark field illumination, normal particles, 

 even when not liberated from the cell, can be observed in the cell 

 itself. When cells, such as those of the rabbit brain or liver, are pressed 

 between cover-glasses and observed, almost the total cell-body appears 

 to be decomposed by the mechanical pressure into minute particles. 



Phage particles can be seen under the microscope, but in the 

 growing young cells no virus-like particles may be observed. However, 

 if bacteria are treated with such chemicals as a salt of heavy metal, 



