-39- 

 the edge of the staining solution (Fig. 31), nor anywhere 

 else on the grid. 



Thin Sectioning 



Tissues examined by electron microscopy could be 

 directly compared to and correlated with those seen by 

 light microscopy when either the 0/G or toluidine blue 

 methods described in this study were used. ORSV 

 inclusions were readily located by light microscopy after 

 the tissues were stained with the 0/G combination and 

 subsequently could be processed for embedding and thin 

 sectioning. After ultrathin sections were made, the same 

 inclusions observed by light microscopy were also seen by 

 electron microscopy. However, the fine structure of the 

 cells and the inclusions at the ultrastructural level was 

 poorly resolved (Fig. 34). When Azure A was used, those 

 fine structures were even more poorly resolved. More 

 satisfactory results were obtained by using the toluidine 

 blue method. Semithin sections (0.5-1.0 /im) were made 

 with an ultramicrotome and stained with 1% toluidine blue. 

 Although this dye stains cell structures in a nonselective 

 manner, the viral inclusions can still be recognized by 

 their characteristic morphology and can thus be 

 differentiated from cell organelles in these semithin 



