Electron Microscopy Observations on a Spontaneous Mastocytoma in a Dog

The ultrastructure of a dog mastocytoma examined with the electron microscope after fixation in glutaraldehyde, post-fixation in osmiumtetroxide and butyl-methyl methacrylate embedding is described. The ultrastructural characteristics with particular regard to the submicroscopic morphology of specific granules were studied in details, also with the aid of comparative observations on thick sections stained by Giemsa and toluidine blue. On the basis of their observations, the authors describe the following characteristics of neoplastic mastcells: microvilli, a well-developed Golgi region, centrioles, mithocondria, ribosomes, endoplasmic reticulum and 4 different types of granules. Other mastcells, with various degree of regressive phoenomena, had almost no microvilli, multiple interruptions of plasma membrane, mithocondrial swelling as well as vacuolar and fibrillar aspect of the cytoplasm. The morphology of different types of intracytoplasmic granules is discussed also in the light of parallel observations made by other authors. Expulsions of granules were not observed. The hypothesis of the phospholipidic nature of the lamellar component of granules is suggested.