THE MORPHOLOGICAL APPROACH 95 



whether virus may be multiplying in the cytoplasm or the nucleus. The mito- 

 chondria, however, seem both in the nerve cell and tissue culture to remain 

 unaffected until fairly late in the destruction. 



C. Encephalitis 



Although there have been relatively few cytological studies of the effect of 

 the arbor (arthropod-borne) viruses on cells, these do illustrate certain 

 general problems and so will be discussed here. The virus of eastern equine 

 encephalomyelitis produced varying degrees of gross destruction of cells in 

 tissue culture, dependent upon the cell strain used (Bang and Gey, 1952; 

 Bang et ah, 1957). Using a tissue culture method of preparing cells for 

 electron microscopy, the cytological aspects of these infections were studied. 

 It was shown (Bang and Gey, 1952) that piecemeal destruction of the cell 

 occurred. Individual fibrillar processes (Fig. 13). normal for the rat fibroblast, 

 were destroyed by the virus before any effect on the rest of the cell was apparent. 

 In other cells, the virus was found on the very edge of the cell, sometimes in 

 the presence of destruction, sometimes without any change. Subsequent 

 quantitative studies by Dulbecco of virus release from cells showed that this 

 virus is gradually released from cells over a period of some hours. 



This picture of varying or limited amounts of destruction is completely 

 changed when the same virus is studied in primary explants of chick em- 

 bryos, either in roller tube cultures (Bang, 1955a) or in slide cultures (Bang 

 and Gey, 1949). Here, the destruction was shown to be accompanied by an 

 almost complete replacement by the virus. 



A somewhat related virus (Egypt 101) has been studied by the fluorescent 

 antibody technique not only in mouse brain but also in cultures of human 

 epidermoid carcinoma (Noyes, 1955). The antigen was found 24 hours after 

 infection in the cytoplasm, but there was no nuclear staining. There was 

 some concentration of the antigen in the paranuclear area at first, but later 

 it was found distributed throughout the cytoplasm. 



XI. Tumor Viruses 



Three fundamental questions may be raised concerning tumors induced 

 by viruses: 



1. Are cells which are infected by neoplastic viruses morphologically 

 different from cells infected with other viruses? Specifically, are there differ- 

 ences in the localization of the virus, the alterations hi ultrastructure in the 

 cell, the mitotic abnormalities, and the mechanisms of virus multiplication 

 and virus release? 



2. Is there any direct relationship between the presence of morphologically 

 identifiable virus and the malignant nature of the cell? Are there reliable 



