Document Qkzd5EqbN6rwb4Y2ZzOrkyO5k

-ommctl mainly > recognizable st nmscs were uneter (Figs. 5 nple these were ake lining mix!iat consisted of icklition to tin* iare.nt.lv normal ess than 1of hers by sincle normal phag.few days after d these smaller :ontained some 0). The larger as with heated CHRYSOTILE ASBESTOS AND AUTOMOBILE BRAKE LINING DUST JJ49 etiun of brake mm fine wun.'sidiml bodies. Fro. 7. A particle of brake lining dust within a mouse macrophage 2 wk after the injection of this dust. In this instance the dust consists of low density amorphous material within which are embedded recognizable crystals of chrysotile asbestos (C) and larger nonfibrous crystalline particles that probably represent metallic aluminum (A). X 63,000. chrysotile many of the larger particles although surrounded by cells, remained extracellular. Dead macrophages containing brake lining dust were found in the granulomas at all stages of the experiment, but they were less frequent than in granulomas produced by chrysotile heated to either 800C or 1000C. DISCUSSION The present study has confirmed previous suggestions that the physical shape of asbestos particles is important in determining the degree of fibrosis produced in t ssues. Several workers including King et ul. (1946), Vorwald et a]. (1951), and Webster (1965) have suggested that long fiber asbestos is more fibrogenic to lung tissue than short fiber dust and Davis in 1972 showed that this also applied to dust injected into the pleural cavity. It was found in this work that long fiber samples of a number of mineral dusts produced much more fibrosis than short fiber dust. In the studies using heated chrysotile it was found that if the dust was heated to no more than 400"C mechanical grinding still produced dust contain ing a large proportion of long fibers. When normal chrysotile is finely ground the original crystal bundles tend to split longitudinally rather than transversely and therefore very long thin fibers are produced. Sieving this dust removes most