62 AN INTRODUCTION TO THE STUDY OF VIRUSES 
for the type of membrane used the A.P.D. to the size of the particle 
just stopped by the membrane. This is the method used by Elford 
(1931). 
TABLE III 
THE PARTICLE SIZE OF SOME REPRESENTATIVE 
VIRUSES AND PROTEINS 



Virus | ze | Method of Measurement 
Bacteriophage S 13 . : : 8-12 ultra-filtration 
Bacteriophage staph. (Northrop) . 550-670 centrifugation 
Equine encephalomyelitis virus ; 32-39 centrifugation 
Foot-and-mouth disease virus . ; 8-12 ultra-filtration 
Gipsy moth virus (L. dispar) . : 415 X 160 electron microscope 
(virus bundles) 
Influenza A virus . : : ; 80-120 ultra-filtration 
Potato virus X 3 : E , 9°8 X 433 centrifugation 
Psittacosis virus. : : j 280 x 380 | visible light microscope 
Southern bean mosaic virus. ; aa sedimentation, diffusion, and 
viscosity measurements 
Tobacco mosaic virus. : 7 ES, 6 275 electron microscope 
One of the tobacco necrosis viruses . 20 electron microscope 
Tomato bushy stunt virus 5 : 26 electron microscope 
Turnip yellow mosaic virus. : 19°5 electron microscope 
Vaccinia : F é : : 240 X 170 electron microscope 
PROTEINS 
Helix haemocyanin : : P 31 centrifugation and _ electron 
microscope 
Horse methaemoglobin . . : 577 X-ray diffraction 
_— 

The recent method of radiation inactivation is based on the fact 
that, when a virus is inactivated by ionizing radiation (i.e. X-rays or 
a radio-active radiation, but not ultra-violet light), it is possible to 
calculate from the amount of inactivation produced by known doses 
of radiation what may be called the radio-sensitive volume of the 
