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W, SCHAFER 



in vertical section and approximately rectangular in horizontal section. 

 This inner body consists of DNA and protein. It is surrounded by a 

 protein coat (b). A further structural element (c) is located in a central posi- 

 tion above and below this protein coat, and is claimed to be protein. The 

 entire mfective particle is bounded by a membrane, which consists of two 

 layers and probably contains lipid, as weJl as other components. The nucleo- 

 protein inner body, which can only be seen clearly after treatment of the 

 virus particle with pepsin, varied considerably in size and form in the studies 

 of Peters and Nasemann (1953). Along with various transitional stages, some 



Fig. 1. — Structure of the mfective particle of vaccinia (Peters, 1956). 



particles were observed that no longer had any pepsin-resistant central body. 

 These particles were not characterized biologically. They bring to mind the 

 nucleic acid-deficient S antigen of poliovirus. Since they are of lower mass, 

 they are probably not present in the preparations purified by ultracentri- 

 fugation and studied by the other chemical methods. 



Of the virus-specific products which accompany the infective particles the 

 LS antigen has been most completely studied. It has been isolated from virus- 

 free filtrates obtained from the extracts of infected dermal pulp of rabbits. It 

 can be highly purified by precipitation at a suitable pH (isoelectric point, 

 pH 4.8) (Craigie and Wishart, 1936; Shedlovsky and Smadel, 1942). Such 



