16 



I. INTRODUCTION TO VIRUSES 



periods the diminution rate became constant and the water content 

 would decrease rectilinearly. If we assume that the decrease in the 

 water content with a constant rate is due to the squeezing out of the 

 water contained in the particles and that the rapid decrease at the 

 beginning of the centrifugation with an inconstant rate is due to the 

 pressing out of the water interposing among particles, the water con- 

 tent of the particles can be estimated by measuring the content at the 

 period when the decreasing rate will become constant. In this manner, 

 with both vaccinia and phage, it was estimated to be about 90 per cent. 

 In Fig. 1 was shown the experimental result obtained with phage 

 particles. Such a result was obtained without any concern with the 

 virus activity, no differences being found between virus particles and 

 the normal ones. In the case of plant particles, after a certain period 

 of centrifugation the water content of the precipitate tended to become 

 constant as shown in Fig. 2. Accordingly, in such a case the water 

 content can be estimated more accurately than in other cases. 



20 'til 60 8S) WO 1Z0 T*0 

 Time of centrifugation in minutes. 



180 



Fig. 2. Centrifugal precipitation of vegetable protein particles from 

 the leaves of B. chinensis L. var. oleifera Makino. 



Secondly, it was calculated from the sugar-insoluble space of the 

 particle that approximately 10 cc. of water was combining with 1 g. of 

 dry particles ; the sugar-insoluble space of the particle was calculated 

 from the concentration of a sugar in the solution in which the virus 

 particles were suspended. The sugar concentration was measured 

 after a known quantity of the sugar had been fully dissolved in a 

 known volume of the virus suspension from which the particles were 

 subsequently centrifuged off. Experimental data obtained with vaccci- 

 nia virus particles are shown in Fig. 3. 



Thirdly, by counting the particle number under the ultramicroscope 

 the average diameter of dry particle was calculate^! to be about 0.25 jj. 



