XI. WHEN TO USE SPECIAL MICROSCOPES 369 



J. SPECIMENS THAT REQUIRE MANIPULATION 



1. Microdissection, Microincineration, and Radioauto;i^ra]>hs 



Equipment for manipulation of materials under the various powers 

 of the microscope varies from a simple mechanically controlled tool 

 mounted on a base with three mutually perpendicular rack and pinion 

 movements to elaborate controls for needles, knives, or pipets. Some 

 work on a pantograph principle and others have hydraulic controls. 

 The equipment may be adjustable so that the full movement of a con- 

 trol may include only the diameter of the field of view at the magnifi- 

 cation used. The equipment is useful for dissection, exploration of 

 structure, injecting or placing materials and reagents, and still other 

 procedures possible only with high magnifications. Special chambers 

 are required to maintain the proper humidity and temperature for 

 work w4th living tissues. The simplest equipment may be home- 

 made and require little skill and practice for isolating bacteria, yeasts, 

 and spores (4i)- More elaborate equipment requires considerable 

 skill and experience for its efficient use as well as in making the micro- 

 needles and other tools used with it {6, p. 62). Microincineration of 

 tissues on quartz or hard glass slides is possible in a small furnace and 

 the location and identification of mineral components may be de- 

 termined with chemical and other micromethods. Owing to the 

 fragility of the specimens considerable skill and care are required of 

 the microscopist (4,4^)- 



The location of radioactive materials and tagged chemicals in 

 tissues (see also Chapter XVII) may be accomplished by placing 

 the tissue section on a photographic emulsion long enough for the 

 particles, or rays, to affect the plate, developing the plate, and cor- 

 relating the traces in the emulsion with their origins in the cells of the 

 tissue. The phase and darkfield microscopes offer promise in this 

 new and difficult field of microscopy (43) . Useful techniques should 

 include stereophotomicrographs for the lower magnifications with 

 sufficient depth of fields, or divided, double exposures on the same 

 film with part of the exposure at the level of the tracks and part at 

 the level of the tissue. Nonstereoscopic pairs of tracks and of tissue 

 can be superimposed with the stereoscope to aid in locating the origin 

 of the tracks. 



The last two methods require that the microscopist be skilled in 

 preparing and sectioning the material as well as in its interpretation. 



