Abstract

Experimental inhalations of silicon dioxide and tobacco smoke cause a gradual increase in the number of pulmonary macrophages containing metachromatic material within the nucleus and cytoplasm, and they may assume the appearance of mast cells. Many pulmonary macrophages containing metachromatic material were found in anthracotic human lungs.

Histochemical techniques identify this material as acid mucopolysaccharides. After a more prolonged action of pneumoconiotic substances, mucopolysaccharides disappear after hyaluronidase extraction.

On the basis of these findings the increased amount of acid mucopolysaccharides in the connective interstices of the lung during the phase preceding the onset of fibrous lesions is explained by the prolonged irritative action of pneumoconiotic substances, which are believed to determine hypersecretion of acid mucopolysaccharides by the pulmonary macrophages.