II. THE SIZE OF VIRUS PRATICLES U 



It is generally believed that vaccinia virus particles are much greater 

 in size than influenza virus particles, but according to an electron 

 micrographic study by Wyckoff (22) particles similar in diameter to those 

 of influenza have been seen developing from certain cells of chick 

 embryo inoculated with vaccinia. 



At present, the virus size is usually determined by electron micro- 

 graphs, but as we were unable to make use of this method, the particle 

 size was measured by us in the following way : The average dry weight 

 of a single virus particle was first estimated under the cardiod-ultrami- 

 croscope in Beobachtungskammer by counting the number of particles 

 in a virus protein solution of a known concentration, and subsequently 

 the diameter of the particles was calculated from this dry weight. 



Since the diameter is a function of the cube root of the weight, a 

 considerable accuracy should be expected in the values thus obtained. 

 By this method the writer estimated vaccinia virus from rabbit or calf 

 skin tissue to be about 0.25^ (17); this appears agreed well with the 

 value estimated by electron microscope and reported by other workers. 



At any rate, it seems probable that the particle size is in the main 

 subjected to the host cell in which the virus was produced. If viruses 

 are to be produced from the protoplasm, it should naturally be expected 

 that not only particle size but also many other properties are more or 

 less governed by the host cell. In fact, it is actually shown that even 

 the chemical composition of a virus appears sometimes to vary with the 

 source from which it was isolated. 



Thus, the work of Knight on influenza virus indicated that the 

 virus particles isolated from mouse lungs or from embryonated hen's 

 eggs possess an antigenic moiety characteristic of the respective host, 

 although they seem to be homogeneous, electrochemically and in sedi- 

 mentation behaviours (23). It was also confirmed that chicken tumour 

 virus bears a resemblance in its chemical composition as well as in the 

 immunological property to normal particles isolated from the chicken 

 tissue (24) (25). With equine encephalomyelitis virus a similar fact is 

 known : The virus isolated from embryonated hen's eggs resembles 

 remarkably in the immunochemical behaviour to the normal component 

 (26) (27). Poison and Wyckoff, investigating 17 kinds of amino acids, 

 found that there was no significant difference in the chemical composi- 

 tion between E. coli and its phage (28). 



2. Difference in the Resistance of Virus due to Particle Size 



Virus preparations obtained by our method appear in the main to 

 consist of homogeneous particles under the microscope, but if examined 

 carefully it will be revealed that this is not the case. We were able to 



