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An evaluation of the ultrastructure of the myeloma cell in 19 cases confirms its marked pleomorphism. It ranges from a cell indistinguishable from the normal plasmacyte or its precursors to a cell with clearly abnormal configuration. Abnormal features included abnormalities in size and shape of the cell, nucleus, nucleolus and mitochondria; nucleocytoplasmic asynchronism; disorganization, atypical location and hypertrophy of the Golgi apparatus; and the presence of multiple centrioles. Six types of arrangement of the endoplasmic reticulum were differentiated. In certain cases there were cells with seemingly intermediate features between the lymphocyte or the reticulum cell and the plasma‐myeloma cell. Intranuclear and different types of cytoplasmic dense (osmiophilic) bodies were observed. These bodies likely represent condensed protein and some may be lysosomes. Some morphologic features suggest that the Golgi apparatus plays a role in the condensing process. The myeloma cell releases its secretion mainly by clasmatosis or cytoplasmic fragmentation.

A survey has been made of granulomatous lesions found in sections of bone marrow from 150 patients studied at the Mayo Clinic. These lesions have been found in a variety of disorders, some with known etiologic agents and others with unknown causes. With the exception of tuberculosis, histoplasmosis and brucellosis, in which the causative organisms were seen and identified bacteriologically, the granulomatous lesions were not thought to have any distinctive histopathologic characteristics. Prominent lesions, Langhans’ giant cells and necrosis were more common in the marrow of patients with disorders known to be associated with a granulomatous inflammatory process than they were in associations with other conditions.