Light and electron microscopic histochemistry was carried out on the serous secretory granules of the parotid acinar and sublingual demilunar cells of the Mongolian gerbil. These are bipartite in structure with a central dense core and a rim of lower density. Light microscopic techniques included staining of sections with Alcian blue and PAS reaction before and after sialidase digestion. PA-methenamine silver, dialyzed iron, colloidal thorium and ruthenium red reactions for mucosubstance were compared on control and pronase digested materials. The results obtained have been interpreted to indicate that the peripheral rim of the granules contained mainly sialomucin whereas the central dense core was rich in protein. Freeze-etched replicas and frozen thin sections of the gerbil salivary glands revealed the bipartite substructure of the granules to be a consistent structure regardless of specimen preparation procedures.
The secretory granules in the serous acinar cells of the monkey submandibular gland which also have a central dense spherule and a rim of lower dense matrix were tested in the same way with the PA-methenamine silver method. A positive reaction was limited to the rim of lower density matrix, indicating that this granular matrix is rich in carbohydrates in contrast to an unstained dense central spherule which is digested with pronase. Morphological and cytochemical similarities of the granule content between species are compared.