Evening star., 1938-12-17
OF Stars, Men
And Atoms
Notebook Of Science Progress
In Field, Laboratory
And Study
By Thomas r. Henri.

By Thomas r. Henry.
Stuck-in-the-mud brain cells unable
to make the grade on the uphill road Of
evolution, constitute an important factor
| IN hereditary -mindedness
This appears from an intensive study
of the brain of an 8-month- -old feeble
minded child just made by DR.. P. A. Fitz-
gerald of University College, Dublin, who
has been working at the embryological
laboratory of the Carnegie Institution OF
Washington. This brain happened to be
an almost ideal specimen by which DR..
Fitzgerald could study the mechanisms
by which are built up the top layers of
the cerebral cortex, found only in human
beings and the higher apes.
Ordinarily the surface of the brain is
extremely corrugated, in distinction to
the almost smooth brains of the lower
animals This particular infants brain
was noteworthy because its whole CEN
tral portion, wherein are located the
centers of feeling and movement, was
smooth as the surface Of a billiard ball.
| Both its back where is located the CEN
ter of vision, and the front were as well
developed as those of normal infant of
that age.
1t was a case, the Carnegie embryolo-
gist deduced, in which the mysterious
| processes of brain formation could be ob-
served where they had halted at mid
way stage. The smoothness of parts of
the brain surface in mental detectives
had haon haF
strikingly as in this specimen. DR.. Fitz-
gerald was especially interested in get
ting to the bottom of the processes
which cause the top of the cortex to form
IN folds, depressions and ridges The
surface survey, according to the report
OF the work made to the trustees of the
Carnegie Institution, was followed by an
intensive microscopic study OF cross sec
tlons OF the brain In order to determine
what had happened to various types of
nerve cells which make up the completed
structure
The normal human BRAIN DR.. Fitzger-
aid explains, has a six-layered covering
OF nerve cells. This is the cerebral cor
tex the organ Of voluntary movement,
thinking and conscious life.
At first there is only a single layer, the
so-called ventricular apendyma. This
parity lines the inner surface of a hol-
low ball. Rather late in the course of
embryonic life the cells of this layer, i'm
pelled by some impulse which remains
obscure, begin to multiply and migrate
upward through the wall of this hollow
pail. With all the precision of soldiers
on parade they form themselves into the
different layers, one after another.
The nerve cell migration is far from
complete when a child is born. The bot
tom three strata are nearly complete.
but the upper three can barely be dis
cerned. The same condition is found in
the mature brains of such mammals as
the cat and the dog. Quite rapidly after
olrtn, however, the full human brain
rapidly takes shape. When the upward
migrating cells reach the place where
they are to stay they send out white
nerve hbers which extend downward to
make connections with lower brain and
spinal cord centers.
among the last brain cells to start
their migration are the Betz cells the
largest in the brain, which ordinarily are
found chiefly in the area Just in front of
tne center OF the cerebral corteX. It is
IN this area that all voluntary move
ments are initiated The Betz cells pre-
sumaoiy are the organs of all movements
which are not automatic reffexes.
THESE big cells can easily be dis
tlngushed under microscope and fur
nlsned Dr.. Fitzgerald with his chief clue
only very few of them were found in
the cerebral cortex itself, but they were
found stranded all the way through the
thick layer of nerve flbers which had
been laid down by the cells of the lower
three layers. The first two layers were
entirely absent.
1hey were like the heavy artillery of
an army advancing into positions whose
guns get hopelessly stuck in the mud all
along the line and have to be abandoned
Ihus the brain army's battle with life is
lest before the fighting actually starts.
Apparently it is in the first three law
ers, especially the second and third, that
the plling up of rising nerve cells, COM
olned with certain mechanical forces,
causes tne formation of the very rough
surface, covered with hills and valleys.
which is characteristic of the human
oraln. Ihe lower one goes down the evo-
lutlonary tree OF the species the smoother
the top layer of the brain and the less
the intelligence.
There are two possible explanations
Tor the failure of the cells which should
nave formed the upper layers to reach
their destination, DR.. Fitzgerald says.
One is that they were poor soldiers in
the flrst place, born without the stamina
for the hard uphill march required of
them. This would be a condition con-
genital with the individual and explains
IN part the hereditary mechanism of
feeble -mindedness. The other is that
they were poisoned by some toxins in
mothers body and weakened, like sick
soiolers, so that they had to fall by the
wayside.