MORPHOLOGY 



955 



left between them. Ultra-violet photographs show a more highly refractive out- 

 line corresponding to the periphery of the cell, and often an increased density 

 at the poles. Whether these appearances are due to the presence of a cell-wall 

 and to polar condensation of the cytoplasm respectively, or are merely the effects 

 of interfacial phenomena, it is impossible to say. The foot-and-mouth virus, 

 which is among the smallest of the viruses, is, according to Barnard (1937), rod- 

 shaped, the length being sometimes as much as three times the breadth. 



TABLE 59 



Approximate Sizes of Filtrable Viruses 



Staphylococcus 



Bovine pleuropneumonia spheres 



Rickettsia 



Psittacosis 



Pseudo-lymphocytic choriomeningitis 



Vaccinia 



Canary-pox 



Bovine pleuropneumonia particles . 



Rabbit fibroma 



Rabbit myxoma 



Lymphogranuloma 



Sandfly fever* 



Herpes 



Ectromelia 



Rabies 



Pseudorabies 



Borna disease 



Newcastle disease 



Influenza B 



Russian spring-summer encephalitis 

 Staphylococcus phage .... 



Influenza A 



Swine influenza (American) . 



Vesicular stomatis 



Rous sarcoma 



Fowl plague 



Staphylococcus K phage .... 

 Flexner dysentery phages D4, D12 



,000 



300 



275 

 190 



>150 



,125 



HOO 



I 90 



85 

 > 75 



. 62 



Staphylococcus phage 

 Lymphocytic choriomeningitis 

 Durand's disease .... 



m^ 

 50 



40 



35 

 33 

 30 



* Alternative size 



Coli phage 



Shiga dysentery phage D54 . 

 Salmonella phage S41 ... 



Rabbit papilloma 



Megatherium phage 



Infectious ansemia of horses. 

 Tobacco mosaic (long diameter) 



Rift Valley fever 



American equine encephalomyelitis. 



CoU phage C36 



Flexner dysentery phages D13, D20, D48 



St. Louis encephalitis 



Japanese encephalitis 



West Nile encephalitis 



Louping-ill 



Hsemocyanin molecule {Helix) . 



Coli phage C13 ^ 



Salmonella phage S13 >18 



Yellow fever J 



Foot-and-mouth disease i 



Poliomyelitis llO 



Mouse encephalomyelitis J 



Edestin molecule 8 



Serum globulin molecule 6-3 



Serum albumin molecule 

 Oxyhaemoglobin molecule 



Egg albumin molecule 4 



given as 20-40 m/x. 



>25 



22 



5-6 



Further information on the shape, size, and structure of the viruses is being 

 afforded by the electron microscope. By its use the elementary bodies of vaccinia 

 appear to be brick-shaped, to possess some sort of limiting membrane, and to 

 contain fine circumscribed areas of greater density arranged like the spots on 

 dice (Green et al. 1942) (see Fig. 233). 



The size of many viruses has now been calculated, mainly from data based 

 on the use of Elford's gradocol membrane technique, and to a less extent from 

 the microscopical photographs of Barnard, the electron micrographs of American 

 workers, high-speed centrifugation, and the rate of diffusion of virus particles 

 in a suitable medium. These different methods do not always agree in their 

 results. By the filtration method, for example, the figure reached tends to corre- 

 spond to the size of the smaller particles, by the centrifugation technique to the 



