'GRAY' AND 'WHITE' MATTER.--The 'gray matter' of the brain and cord is
made up of nerve cells and their dendrites, and the terminations of
axons, which enter from the adjoining white matter. A part of the mass
of gray matter also consists of the neuroglia which surrounds the nerve
cells and fibers, and a network of blood vessels. The 'white matter' of
the central system consists chiefly of axons with their enveloping or
medullary, sheath and neuroglia. The white matter contains no nerve
cells or dendrites. The difference in color of the gray and the white
matter is caused chiefly by the fact that in the gray masses the
medullary sheath, which is white, is lacking, thus revealing the ashen
gray of the nerve threads. In the white masses the medullary sheath is
present.
