148 



MACROMOLECULAR COMPLEXES 



tions of fine structure. In osmium-cryofixation preparations, most 

 of these granules show a characteristic highly ordered paracrystalline 

 arrangement (Figs. 20, 21). Depending on the plane of sectioning, 

 a typical cross-grating pattern formed by dense round or polygonal 

 structures 30 to 40 A in diameter with a regular spacing of 50 to 60 A 

 is seen; or line patterns with the same spacing. This type of organ- 

 ization, which closely resembles the paracrystaUine structure de- 



Fig. 20. High-resolution electron micrograph of ultrathin section of para- 

 crystalline granule from pigment epithelium of guinea-pig retina, showing 

 highly regular arrangement of the constituent dense particles, 30 A in diameter, 

 with an average spacing of 50 to 60 A. Osmium-cryofixation preparation. 

 X 300,000. 



scribed in the inclusion bodies of certain insect viruses and other 

 biological paracrystalline components, is clearly different from the 

 compact lamellar systems of the myeloid bodies and other lamellated 

 corpuscles with a period of 40 to 100 A, as described by other 

 authors (Porter, 1957; Yamada et at., 1958). Examination of a large 

 number of sections discloses characteristic transitions between the 

 mitochondria and these dense pigment granules (Fig. 18). The 

 lamellar structure of the mitochondria shows dense patches of gran- 



