Review of the significance of fibre size in fibre-related lung disease: a centrifuge cell for preparing accurate microscope-evaluation specimens from slurries used in inoculation studies.

Intratracheal, intrapleural and intraperitoneal inoculation studies in animals are widely used for identifying important factors in the pathogenicity of fine fibrous particles and estimating the potential of new materials to produce human pulmonary disease. Evidence on the significance of fibre size is reviewed, with emphasis on direct data derived from airborne fibres in asbestos mines and fibres retained in the mineworkers' lungs. This evidence indicates a need in mesothelioma-related inoculation experiments for means of measuring fibres down to 0.01 microns in diameter. A test cell, developed for preparing microscope-evaluation specimens from injection slurries, has a sector-shaped sedimentation chamber and is used in a swing-rotor centrifuge. To minimize re-formation of aggregates that are dispersed by shearing forces during sedimentation, a sample of the slurry is diluted beforehand to a degree indicated by the length of the longest fibres seen in the light microscope. Fibres and other particles are collected as a uniform deposit on a collodion film enveloping a microscope cover-glass. Current techniques are used to prepare specimens from films for light microscopy, scanning electron microscopy and the transmission electron microscopy which is so necessary for measurement of very fine fibres. Applications of the cell to fibre samples from other sources are outlined.