92 F. B. BANG 



"apparently verging on extrusion from the cytoplasm." In addition to actual 

 destruction of the nucleus in the terminal stage of the infection, small 

 eosinophilic intranuclear inclusions were sporadically found. 



Electron microscope studies of cells of the central nervous system infected 

 with poliomyelitis have not been reported. However, the identification of the 

 Nissl substance which is first destroyed by virus as endoplasmic reticulum 

 (Palay and Palade, 1955) and the presence of quantities of this material at 

 the tips of the dendrites adjoining axons (Palay, 1956) would suggest that the 

 virus is able to parasitize susceptible material throughout the cytoplasm of 

 these specialized cells. 



2. Tissue Culture 



Living nerve cells have been studied in relation to the effects of the virus 

 upon them in tissue culture. In all three types of virus (Hogue et al., 1955, 

 1958), the first identifiable lesion was contraction and disintegration of the 

 extended dendrites. Contraction began at the tips of these long processes 

 and progressed until a process had withdrawn, at times leaving a bulbous 

 extrusion. Later the cell became granular, lost its surface film, and assumed 

 the character of a loose mass of granules surrounding the nucleus. Serial 

 photographs demonstrate these changes. Although pinocytosis has been seen 

 to occur at the tips of the axons in nerve cells in tissue culture (Hughes, 1953), 

 the role of this event in susceptibility to virus has not been considered. 



B. Epithelial Cells and Fibroblasts 



There have been many careful studies of the effect of poliomyelitis 

 virus on tissue culture cells other than nerve cells. These include phase 

 (Stoler and Gey, 1953; Barski et al., 1955; Riessig et al., 1956; Klone, 1955a; b) 

 and bright field (Harding et al., 1956) studies on living cells (Figs. 14, 15). 

 There have also been several sequential studies of such changes in which 

 cells were stained and fixed in correlation with the time of virus release 

 (Biessig et al., 1956; Dunnebacke, 1956a). 



1. Morphological Changes Observed in Living Cells 



The sequence of changes has been studied in individual cells by phase 

 microscopy. Klone (1955a) followed the effect of virus on monkey kidney 

 cells which showed no lesions 23 hours after infection. These retracted from 

 surrounding cells at 25| hours, the nucleolus lost form, and protoplasmic 

 extrusions appeared. Mitochondria remained normal through all of this 

 activity. At 26-| hours the cellular contraction continued, and the sharply 

 defined, irregular cell extrusions progressed. By 27| hours the extrusions 

 developed a series of fine extensions and branches, the cell nucleus was only 

 obscurely visible, and vacuoles appeared in the cytoplasm. In the course of a 



