The pathogenic nature of finely particulate silica.

Silicon is the second most abundant element in the earth's crust. Because of the solubility of silicates of alkali metals a considerable quantity of silicon is absorbed by plants and variable amounts are ingested with plants by animals. Of the amount ingested a small proportion gains an entrance into the body and is distributed in all tissues. The question which has been entertained by many workers is whether silicon is an essential element in animal metabolism. On certain theoretical grounds silicon is considered to be classified among those possibly essential (1)