THE MORPHOLOGICAL APPROACH 91 



same general thickness as the virus particles themselves, would contain 

 different proportions of the virus particles, dependent upon the amount of 

 spherical virus caught in the particular section. Low and Pinnock (1956) 

 have further analyzed these appearances and rule out other arrays as explain- 

 ing the pictures obtained by Morgan et al. (1956b). Recent proposals by 

 Valentine and Hopper (1957) that the true shape of the virus is polygonal 

 (as seen in dried specimens), and that the shape is dependent upon the method 

 of preparation (Tousimis and Hilleman, 1957) may have relevance to this 

 characteristic crystalline pattern. Bloch et al. (1957) studied intranuclear 

 lesions from the same nuclei in Feulgen-stained and in electron microscope 

 preparations. By studying alternate thin and thick sections of HeLa cells 

 infected with types 3, 4, and 7, the intranuclear Feulgen-positive masses 

 were positively identified with the ordered arrays of virus particles (Figs. 11, 

 12). It was proposed that the virus particles developed from a Feulgen- 

 negative matrix. It was further suggested that viral and host DNA may be 

 differentiated by their reaction to a Feulgen azure-staining method. Finally, 

 type 5 virus infection of another cell type (Hep 2) has been shown to contain 

 an unusual crystalline protein within the infected nuclei. This new crystal- 

 line lattice consists of much smaller units and the complete inclusion is 

 Feulgen-negative. 



It is clear from all of these studies that an exciting beginning to the study 

 of intracellular lesions with this virus has been made. The dynamic aspects 

 will need not only sequential studies, but living cells and stained preparations 

 must be analyzed with fluorescent antibody. 



X. Poliomyelitis and Other Neurotropic Viruses 



A. Nerve Cells 

 1. Classic Findings 



Until the relatively recent evidence that a variety of tissue culture cells 

 was susceptible to poliomyelitis (Enders, 1954), attention had centered on the 

 lesions of the central nervous system and preeminently on the anterior horn 

 cell. Although the pathology has been fully reviewed (Bodian, 1948; Howe, 

 1952), the main points will be recapitulated in comparison with lesions 

 produced in the tissue culture system. The progressive changes begin with an 

 initial massing of chromatin, continue with chromatolysis, which progresses 

 even while mitochondria remain intact (McCann, 1918), and proceed eventu- 

 ally to complete necrosis of the cell and subsequent variable neuronophagia. 

 Of particular interest now are some samples of a motor nerve cell lesion which 

 was occasionally present after the acute stage of paralysis (Bodian, 1948). 

 This lesion comprised a large eosinophilic mass, sometimes with the nucleus 



