he thin section, as the early workers
examined it, was practically colorless, and even the crudest details of
its structure were made out with extreme difficulty. Remak did, indeed,
manage to discover that the brain tissue is cellular, as early as 1833,
and Ehrenberg in the same year saw that it is also fibrillar, but beyond
this no great advance was made until 1858, when a sudden impulse was
received from a new process introduced by Gerlach. The process itself
was most simple, consisting essentially of nothing more than the
treatment of a microscopical section with a solution of carmine. But the
result was wonderful, for when such a section was placed under the lens
it no longer appeared homogeneous. Sprinkled through its substance were
seen irregular bodies that had taken on a beautiful color, while the
matrix in which they were embedded remained unstained. In a word, the
central nerve cell had sprung suddenly into clear view.

A most interesting body it proved, this nerve cell, or ganglion cell,
as it came to be called. It was seen to be exceedingly minute in size,
requiring high powers of the microscope to make it visible. It exists in
almost infinite numbers, not, however, scattered at random through the
brain and spinal cord. On the contrary, it is confined to those portions
of the central nervous masses which to the naked eye appear gray in
color, being altogether wanting in the white substance which makes up
the chief mass of the brain. Even in the gray matter, though sometimes
thickly distributed, the ganglion cells are never in actual contact one
with another; they always lie embedded in intercellular tissues, which
came to be known, following Virchow, as the neuroglia.

Each ganglion cell was seen to be irregular in contour, and to have
jutting out from it two sets of minute fibres, one set relatively short,
indefinitely numerous, and branching in every direction; the other set
limited in number, sometimes even single, and starting out directly from
the cell as if bent on a longer journey. The numerous filaments came to
be known as protoplasmic processes; the other fibre was named, after its
discoverer, the axis cylinder of Deiters. It was a natural inference,
though not clearly demonstrable in the sections, that these filamentous
processes are the connecting links between the different nerve cells and
also the channels of communication between nerve cells and the periphery
of the body. The white substance of