Abstract
The radial components of the myelin sheath in the optic nerve of frogs (Rana pipiens) have been studied by electron mincroscopy. The nerves were fixed in OsO4 or KMnO4, embedded in methacrylate or epoxy resin, and, after sectionings, non-stained or stained with either potassium permanganate or plumbite ion method. The results obtained are summarized as follows:
1. The radial components are present in some of the myelin sheath of the optic nerve of the frog, Rana pipiens.
2. The radial components in transverse sections of the myelin lamellar layers appear as a series of small thickenings which are present in the interperiod lines of the myelin lamellae and stand in several rows arranged radially across the thickness of the myelin sheath. The dense period line of the myelin sheath at the site of the radial component somewhat increases the electron density. In oblique sections of the myelin lamellae the radial components appear as dense lines which show a parallel array running across the thickness of the sheath.
3. The thickness of the myelin lamellae increases at the site of the radial components.
4. The rows of the thickenings in the radial components show two different patterns of distribution in the myelin sheath; the diffuse and condensed types. The former is scattered in a relatively large part of the myelin sheath and shows a fairly large interval of 500 to 600Å between the individual rows, while the latter occurs in a small limited area of the sheath in group of many parallel rows showing a relatively small interval of 150 to 270Åbetween each rows.
5. Most of the rows of thickenings extend throughout the thickness of the myelin sheath, while some of them extend for only a part of the superficial layers of the myelin lamellae.
6. Sometimes the rows of the radial components extend continuously over two adjacent myelin sheaths which come into intimate contact side by side with each other.
