II. THE SIZE OF VIRUS PARTICLES 19 



water. It is worthy of note that this water was claimed to exist in 

 forming a water layer several molecules thick surrounding the particle 

 as in the case of vaccinia virus, since X-ray pattern from the internal 

 structure of the particles was found similar for dried virus and for virus 

 in solution. 



Not only protoplasm protein particles, but also usual protein mole- 

 cules in solution seem to be combined generally with great quantities of 

 water. From X-ray analysis Crowfoot (41) estimated the water contents 

 of crystalline haemoglobin and lactoglobulin to be respectively 46.6 and 

 40.8 per cent. Bull (42) stated that a crystalline protein combined so 

 much water as 83 per cent in the saturated water vapor. 



There seems no doubt that the majority of water quantity, proved 

 by the writer to exist in the association with the virus particle, is pre- 

 sent outside the particle in forming a thick water layer, although the 

 true water content, /. e., the water present inside the particle must 

 also be considered. Thus the diameter of the hydrated particle should 

 be much greater than that of the desiccated one. Nevertheless, viruses 

 were previously called ultramicroscopic pathogens and their invisible 

 nature was looked upon even as one of their characteristics. In fact, 

 vaccinia virus particles, isolated by our method, whose diameter even 

 in the dry state is so large as 0.25 /j are never visible under the 

 ordinary microscope if examined in a neutral solution, but usually will 

 become visible when the pH of the solution is adjusted to a weakly acid 

 pH near the isoelectric point and stained properly with fuchsin water 

 solution. 



This remarkable property of the virus may probably be due to the 

 thick water layer surrounding the particles as well as the true high 

 water content. The fact that the particles become visible at a weakly 

 acid pH may be ascribed to the minimum swelling at the isoelec- 

 tric point. 



Bacterial cells infected with phage are known to swell up and 

 become invisible before bursting into phage particles. We could like- 

 wise ascertain this phenomenon (9) which may be attributed to the 

 water molecules sttracted by the lyophylic groups which may be libe- 

 rated in the course of the coagulation or the denaturation of the pro- 

 toplasm by phage infection. 



