ELECTRON MICROSCOPY OF VIRUSES 67 
patches can be seen in the virus particles indicating some kind of 
internal organization. This central “nucleus” of dense material 
has been investigated by McFarlane and Dawson (1948) after special 
treatments. Two important chemical reactions of viruses which are 
Open to examination under the electron microscope are their inacti- 
vation by various methods and their neutralization by specific antisera 
or, to put it another way, the antigen-antibody reaction. Not much 
work has been done on the microscopy of inactivation though it is 
known that the virus particles do not appear to have changed much 
after treatment with formaldehyde. The particles of tobacco mosaic 
virus have been photographed after supersonic radiation and have 
been shown to be split up into smaller non-infectious units. 
Anderson and Stanley (1941) have used the electron microscope 
to study the reaction between tobacco mosaic virus and its antiserum. 
Photographs taken of the purified virus alone showed it to, consist 
of particles about 280 mu long and about 15 mu wide. Micrographs 
of a mixture of this virus and normal rabbit serum showed virus 
particles of normal size and indicated little or no adsorption of the 
serum particles on to the virus particles. 
Similarly, no adsorption took place between the tobacco mosaic 
particles and antisera from rabbits prepared against the viruses of 
tomato bushy stunt, potato virus X, and tobacco ringspot. However, 
when its specific antiserum is added to the tobacco mosaic virus, a 
different state of affairs is revealed under the electron microscope. 
When dried on a collodion film an hour after mixing, photographs 
show particles about 300 mu long by 60 mu wide with a charac- 
teristic fuzzy profile. If the mixture is applied to the collodion film 
several hours after mixing, an irregular framework of thickened 
antigen (virus) particles may be seen. It is suggested that the fuzzy 
profile of the virus particles is due to an adsorbed layer of asym- 
metrical molecules from the serum, arranged along the length of the 
particle with their long axes at right angles to the axis of the virus 
particle whilst the irregular framework, formed after several hours, 
may possibly be the antigen-antiserum precipitate. 
A similar study has been made of the antigen-antiserum reactions 
of two viruses, those of tomato bushy stunt and southern bean mosaic 
which have spherical particles, but using the metal shadow-casting 
technique in a pure suspension and at sufficient concentration, those 
viruses show a pronounced tendency to associate in regular crystal-like 
arrays. When mixed with their specific antisera, however, the particles 
