Evening star. [volume] (Washington, D.C.) 1854-1972, 1889-03-27
THE WAY OF THE NERVES.
Reflex Action and Something About Its
Modus Operandi.


| From the London Illustrated News
Underlying all the varied phases of nervous
action, we find one great and guiding princi-
| pie, for the first calculation of which we are
| indebted to the genius of the late DR.. Marshall
Hall. The principle is known as that of reflex
| action and one or two simple illustrations will
| familiarize US with its nature and modus oper-
andi am crossing the street and hear the
sharp trot OF cab-horse Just behind me.
| Anxious to avoid accidents, quicken my steps
and reach the opposite pavement in safety.
What has been the nature and operation of the
nervous mechanism in this case? Waves of
sound from the cabs motion first of all were
received by the drum of the ear. were trans
mitted to the inner ear. were modified and
assorted so as to reach the brain as 'sen-
sations OF sound. and were finally received
and dealt with by that part of the
brain set apart for the control of the hearing
sense. 1hereupon, consciousness of danger to
my personality was awoke. probably because
| the hearing part of the brain communicated
with the intellectual centers. At any rate, the
result of sound-waves striking my ear was the
awakening of my mind to the risk l ran in
crossing the street. Now, this first piece of
nervous play only goes so far as to include the
conveyance to the brain of message Cor
sensation from the outer world. 1t is clear
that, IN order to escape danger. must possess
means OF acting, like an intelligent policeman,
upon information received" Accordingly
the sensation of sound sooner or later is re
hected from the brain centers to other parts
OF the body-namely, the muscles. The latter
organs are stimulated to greater activity, and
am speedily landed on the opposite pavement
out of the way of the cab. Notice, then, that
this illustration presents us with a plain. I'M
vanished story of that ''refex action" which
underlles all our nervous operations. and which.
therefore. forms the foundation of all the acts of
our own lives, OF those OF my cats, and, indeed
REGULATES THE ACTS OF ALL ANIMALS.
When you draw back your head to avert
threatened blow, or when your eyelids close as
some one in play passes his hand rapidly be-
fore your eyes. it is reflex action you again il
lustrate In your movements. The eve receives
and its nerve transmits, a sensation of sight
TO the seelng-center of the brain. Thence is
reflected nervous command to the muscles
OF the neck. or of the eyelids alone. as the case
may be. When my cats are rOmping here and
there, each movement whereby Professor"
escapes his mothers attack is carried out by a
similar reflex action of his nervous system.
When you touch the feelers on a snails head,
and see them fold up in the marvellous fashion
they exhibit and when finally that mollusc
tires into the privacy of its own apartment Gas
represented by its shelly for a time, you are
merely witnessing reflex action in lower life.
The sensation of touch has been transmitted to
the nervous centers OF the snail, and those
centers In their turn have issued
the result Of producing the compulsory retire
ment just named 1t is with this reflex action,
as though one outside official (the sense organ)
receiving message. transmits it to headguart-
ers the brain and nerve ccnter); while the lat
ter dealing with the emergency which has
arisen. issues the commands to other officials
muscles, for example), and these latter carry
out the movements necessary for the welfare
of the state. Even when the mouth waters
at the sight of dainties-a phase of life ex-
tremely well seen in dogs who view from q
point OF expectancy the dining arrangements
their masters-it is reflex action which is re-
sponslble for this peace of physiological fool
lshness. The sensation of sight conveyed to
the brain is 'retiected' to the salivary glands
OF the mouth. and these discharge into the
OF service IN digestion. 1t is simply a matter
OF habit which induces the flow of saliva when
there Is nothing present to taste or to digest,
and, SO far, this action, like many others of
higher and lower life alike, is of
UNCONSCIOUS OR AUTOMATIC KIND.
Study this curious principle of nervous ac-
ton little more closely, one recognizes that
1t depends upon the existence of tolerably
constant series of parts. For example, there
must be an ingoing nerve to carry inwards a
message sensation from the outside world
This Is the ''sensory' nerve of science Then
there must exist a nerve-center, or receiving
office, as we may term it. whereat the message
is received and from which it is reflected, or
retransmitted, as we have seen. Lastly. there
is need OF a second or outgoing nerve which
shall carry this REFLECTED" message to mus
Giles or other organs as the case may be. This
latter nerve, because the effect of its motion is
to produce motion of one kind or another is
called the motor" nerve. These three things
are all that are necessary for the carrying out
Of our ifes acts. Doubtless there is much
more that is complex in the details of reflex
action but its essentials are ~ simDle I baya
described them. In this system of body-teleg-
raphy We see countless messages going in and
out from nerve centers, ruling and controlling
all the affairs of our existence. The BODY in
this view of matters, is a very busy state, whose
officials are i'll perpetual and constant commu-
nication with their heads of departments.
Finally, it must be borne in mind that while
we are conscious of much that We do. we are
also utterly unconscious of vast number of
our actions. When We come to think of it. the
fact of our resembling Messrs. Maskelyne and
Cooks figures, in some respects, is tremen-
dous advantage to us. We have not to think
about every act of life; hence we are saved much
intellectual wear and tear. Reading and
writing, and piano playing, and walking, and
many complex actions. may be and are per-
formed entirely without the necessity for
thought. Getting anything off by heart" as
the schoolboy puts 1T, lis really converting
something which at first cost intellectual effort
into something which is purely automatic in
its nature; and the things which are most ma
chine-like in our actions are Just those which
are most purely ''refex" in their nature. The
Indian thief tickles the sleeping man with a
straw, and causes him, in his sleep, to roll over
on his pillow. so that the valuables beneath his
head may be distracted. This may be an il
lustration of nefarious conduct; but it is, none
the less an excellent example of reflex action
unconsciously performed when human nature
lies still in the silken bonds Of deaths twin
brother, sleep"