404 Special Procedures III (chap. 24) I 



SECTIONING 



Recovery of sections was difficult until Hillier and Gettner (1950) 

 developed a water trough attached to the knife, thereby permitting 

 the sections to float directly onto a fluid surface as soon as they were 

 cut. The trough is filled with 10-40% acetone or ethyl alcohol in 

 water to facilitate the flattening (also see Solelo, 1937). The sections 

 are picked up from the solution onto the coated grids, or, if some- 

 what compressed, are transferred first to 50% alcohol and then to 

 grids. 



For serial sections see Gay arid Anderson (1954), Williams and Kail- 

 man (1954), and Westfall (1961). 



The thickness of the sections can be determined by the color analy- 

 sis of Porter and Blum (1953). While the sections float on the bath, 

 they display interference colors depending on their thickness. Silver 

 indicates a thickness of 20-50 millimicra; gold, 50-80 millimicra; 

 purple, 80-130 millimicra. Silver and gold sections are best for elec- 

 tron microscopy, but as they begin to appear blue or green they are 

 getting too thick for efficient observation. 



Three-dimensional images may be obtained by metal shadowing and 

 this is finding favor with many researchers. Metals, such as silver, chro- 

 mium, palladium, platinum and others are evaporated on the specimen 

 at a small angle. A thin film of the metal covers the specimen except for 

 a "shadow" caused by the specimen being in the way of passage of the 

 metal. From the shape and dimension of the shadow, height and con- 

 tour of the specimen can be observed. (Williams and Wyckoff, 1944; 

 Williams and Backus, 1949; de Harven, 1958) 



Plastic sections can be used for optical examination. The sections 

 (1-2 microns) are dried on a slide, immersed (12-24 hours) in xylene 

 to remove the plastic and then can be stained for light microscopy, or 

 mounted for phase microscopy. (Borysko and Sapranauskas, 1954; 

 Farqiihar and Rinehart, 1954; and Houcks and Dempsey, 1954) 



See also Fernandez-Moron (1960) for the application of low temper- 

 ature techniques for electron microscopy luilizing helium ii. In addi- 

 tion, this source describes the use of a liquid nitrogen stage for cooling 

 specimens during observation in the electron microscope. 



References: Farquhar (1956), Hall (1953), Mellors (1959), and Pease 

 (1960). 



