Abstract
Cells of Listeria monocytogenes, were fixed with OSO4 in acetate-veronal buffer containing CaCl2 and NaCl, and treated with uranyl acetate, and after embedding in methacrylates, the thin sections were examined with an electron microscope. A lower density nuclear region occupying the central area of the cytoplasm is filled with fine fibrils. The cytoplasmic membrane consists of a double layered membrane separated by a lighter interspace. The cytoplasmic membrane invaginates into the cytoplasm and seems to be reorganized into the intracytoplasmic membrane system which appears in electron micrographs in a variety of configurations, such as parallel stacks of membranes, lamellar structures and clusters of vesicles, frequently adjacent to the cell wall and to the newly forming septum, and sometimes extends into the nuclear region. These membrane systems appear in cells at all the stages of cultural development, and even in partially autolysed cells as slightly disorganized structures.
