100 



MICROSCOPY 



thetic plastic materials have been used. Embedding for electTon micros- 

 copy employs a methacrylate polymer— similar to Lucite and Plexiglas— 

 which is prepared from small monomer molecules during the embedding 

 process. 



Slices or "sections" of a block of embedded tissue are cut on a micro- 

 tome, an example of which is shown in Fig. 8-11. The block of material 



Image 



Objective 



Phase plate 



Object 



Condenser 



Annular 

 diaphragm 



Fig. 8-12. Phase contrast optics. The ocular is not 

 shown. Diffracted rays (dashed Hnes) take a differ- 

 ent path through the instrument than direct rays 

 (solid lines). The phase plate modifies and bal- 

 ances the light from the two sources. 



