46 II. FUNDAMENTAL STRUCTURE OF PROTOPLASM 



when its concentration is high, the estimation is impossible by measur- 

 ing the space incapable of dissolving a sugar. 



The routine method of determination of the water content by mea- 

 suring the particle density, which is estimated from the sedimentation 

 rate of the particle in various concentrations of substances, such as 

 sugar, protein, or inorganic salt, also may fail to give any indubitable 

 value, since the substances may penetrate into the particle when the 

 concentration is high as just pointed out. 



For such reasons the writer has been unable to estimate the water 

 amount actually contained in the particle. However, since the ordinary 

 virus particles can be regarded as the elementary bodies of protoplasm, 

 their water content should be similar to that of protoplasm itself 

 whose water content is generally accepted to be about 75 per cent. 

 Now, therefore, argument will be advanced on assuming the water con- 

 tent to be 70 per cent, a little less than that of protoplasm. 



As a particle should increase in diameter approximately by 1.6 

 times when a dry particle absorbes water until its water content be- 

 comes 70 per cent, vaccinia virus particle whose diameter is 0.25 jx in 

 dry state will become 0.4/z on water absorption to this extent. If water 

 is further adsorbed on this swelled particle and the total amount of 

 combined water reaches as great as 10 times its dry weight, the dia- 

 meter must increase again by 1.5 times. In this state, the thickness of 

 the water layer is calculated to be 0.09/i, or 900 A: in this calculation, 

 the density of the dry particle is taken as 1.33, a value which was pre- 

 viously obtained by the writer (7). 



According to the writer's estimation, the combined water amount 

 was similar without reference to the kind of virus. For example, the 

 amount of combined water was estimated to be similar both with vac- 

 cinia vi'/us and phage, whereas the particle of the former was found X.o 

 be greater in diameter as much as 3 times than that of the latter (8). 

 This must be a noteworthy fact, because, if the thickness of the water 

 layer was the same, the combined water amount of phage particle 

 should be far greater than that of vaccinia virus particle, but the fact 

 is that the amount is found to be the same, showing that the layer 

 becomes thinner as the particle becomes smaller. 



In the same way as with the vaccinia virus particle the thickness 

 of the water layer of phage particle is calculated to be 300 A on the 

 assumption that the diameter of the dry particle is 80 m// and its den- 

 sity is 1.45 ; also this value of density was previously estimated by 

 us (9). 



The water molecules forming the layer with such a thickness are 

 considered to behave themselves always in association with the par- 

 ticle. The sugar-insoluble space, as above mentioned, was sometimes 



