[Electron microscopic study of nerve tissue elements of the medullary substance of the canine adrenals].

A study was made of the fine structure of myelinated and nonmyelinated nerve fibers in association with the supporting Schwann cells in the adrenal medulla of the dog. The postganglionic sympathetic innervation of adrenal chromaffin cells is proven indirectlining granules (50--200 nm in size) in axoplasma of non-myelinated fibers, mostly in nerve endings on chromaffin cells.