[Submicroscopical study of the granule-containing cells of bronchial carcinoids]

The submicroscopical structure of three bronchial carcinoids was studied. In all the cases, in the cytoplasm of tumor cells secretory granules formed from cisterns of the Golgi apparatus were found. Two types of granules were observed. The first ones were from 150 to 250 nm in size, the second--from 400 to 600 nm. Granules less than 500 nm in size comprise about 90% and cannot be observed by light microscopy because of the low resolving power of the microscope. It is suggested that the secretory product is eliminated by diffusion through the granular and then plasma membrane. The granules are assumed to be heterogeneous in their chemical composition. Secretion of other compounds in addition to serotonin is presumed. The ultrastructural similarity of the tumor cells and Kulchitsky cells is no proof of theif histogenetic relationship.