Particle Identification

HISTOLOGIC ANALYSIS Many types of particles can be identified histologically if they are within the resolution limits of the light microscope. The "Particle Atlas" may be most helpful in such a situation (14) (unfortunately, no new edition is available). Inorganic particles can be isolated and concentrated for morphologic study by holding an unstained, uncovered paraffin section over a flame until the organic tissue has been incinerated.

QUANTITATIVE STUDIES In most cases, light microscopic observation with polarizing lenses provides sufficient semiquantitative information. However, for research purposes and other special circumstances, mineral particles in lung tissue can be analyzed quantitatively by a multitude of methods, either in bulk (macroanalytic) by X-ray diffraction, X-ray fluorescence, neutron activation analysis, atomic absorption spec-troscopy, or proton-induced X-ray emission spectroscopy, or with microanalytic techniques such as energy-dispersive X-ray spectroscopy and wavelength dispersive X-ray spectros-copy. Many of the advanced methods of microprobe analysis such as ion microprobe mass spectrometry are not readily available. Experts such as Dr. Andrew Churg (The University of British Columbia, Vancouver Hospital, Vancouver, British Columbia) or Dr. Victor L. Roggli (Duke University School of Medicine, Durham, North Carolina) may provide helpful consultation. For an excellent review of these methods, see ref. (15). It should be noted that the results of any quantitative method must be interpreted with some caution because particles tend to be distributed unevenly, which adversely affects the results of quantitative studies, particularly if the samples are small.

For the quantitative evaluation of asbestosis, ferruginous bodies are harvested from the fixed or unfixed lungs by digesting the tissue in 5.25% sodium hypochlorite. The solid residues are collected on membrane filters. The characteristic features of asbestos bodies allow reasonably accurate counts. For a detailed description of current digestion techniques and other methods of counting asbestos bodies, ref. (16) should be consulted. For the semiquantitative demonstration of asbestos bodies, dried scrapings from lung sections are often studied. Ferruginous bodies also can be viewed electron microscopically (17).

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