Transmission electron micrograph of secretory granules in an alpha cell of an islet of Langerhans in the human pancreas. In a number of endocrine glands, the small dense granules are separated from their limiting membrane by a clear zone. It seems likely that this appearance is due to loss of fluid content or extraction of less condensd soluble protein during specimen preparation. This interpretation is made the more plausible by the observation that better fixation of the same cell type sometimes succeeds in preserving material of appreciable density between the granule and the limiting membrane, as illustrated in the following figure.