Injections of stilbamidine cause morphological changes in myeloma cells. During this treatment large basophilic granules appear in the cytoplasm which show a tendency to become confluent. These granules stain red with pyronine and can be visualized in the supravital stain with neutral red. One of the main constituents of these inclusions consists of ribose nucleic acid.
These morphological changes seem to be limited to myeloma cells, since in none of the other bone marrow elements do comparable granules or inclusions develop.