The division of the mature mammalian brain and spinal cord into regions
of "white" matter and "gray" matter is observable upon the most cursory
inspection. Microscopic examination indicates that the "white" matter
regions are characterized by a multilamellar sheath (myelin) which sur-
rounds the axons. A morphologically similar myelin imparts the white
color to tracts of the peripheral nervous system, although, as is empha-
sized throughout the book, there are very significant morphological and
chemical differences between central and peripheral myelin. The rapid
postnatal accumulation of myelin is temporally associated with
increasing functional capacity and presumably indicates some important
role related to neuronal activity. The ability of myelinated axons to
conduct electrical impulses much more rapidly and with much lower use of
energy, relative to unmyelinated axons, is now generally accepted. As is
evident from the above capsule description, a considerable body of
information concerning myelin is available. However, as in other areas
of research the unknown expands before us more rapidly than we are able
to add to our core of knowledge. This is a corollary of the axiom that a
good experiment raises more questions than it answers. Among the areas
currendy under investigation in many laboratories are the following:
interaction of myelin-forming cells with neurons, assembly and metabo-
lism of myelin, molecular architecture of myelin, and the details of the
functional role of myelin.