The Topographic Distribution of Mineral Dusts in Some Pneumoconiotic Lungs

Abstract

All theories that have served to explain the formation of fibrous tissue in silicosis relate the development of the collagen fibers, directly or by inference, to the site of the silica particles. Recent studies1’ 2 have established that portions of some silicotic nodules may contain no demonstrable mineral particles and that dust particles formerly believed to be more or less permanently imprisoned at the site of their deposition within the lung tissue not only may be shifted from one region to another within the lung but may also be expectorated. Thus the occurrence of silicotic fibrous tissue without the demonstrable associated causative mineral particles should be considered no more anomalous than the more familiar finding of manifestly silicotic lungs with a relatively low silica content, that is, a silica content no higher than that of some non-silicotic lungs. Because the topographic study of the distribution of mineral dust in pneumoconiotic lung tissue gives promise of providing new information regarding the pathogenesis of pulmonary dust diseases such studies have been performed on routine cases that have come to the attention of the Industrial Hygiene Foundation. It is the purpose of this paper to summarize the results of some of these studies. Method Formalin-fixed lung tissue was embedded in paraffin, sectioned and stained in a routine manner. In addition replicate sections were also stained by a combination of the Van Gieson stain for collagen and the postassium ferrocyanate method for iron. The locations of selected fields in the stained sections were noted with the aid of a “field finder.”t Following photography of these fields, the sections were incinerated at 550#{176} for one hour, and after cooling, the acid-soluble portion of the ash was removed by placing the slides in concentrated hydrochloric acid for 30 minutes. They were then washed with running tap water, followed by rinsing in distilled water and air drying. The same fields were then rephotographed but under dark field conditions. Composites were made by superimposing the 2�4” x 2�4” dark-field negative upon the bright-field negative or the color transparency of the same field and after careful matching, fixing them in their relative position by means of transparent tape.