Courtesy Readers Digest 1981. November.
From the frontiers of science and the far horizons of
personal courage, these stories of medical triumphs and miracles will reaffirm
your faith in the awesome powers of the human spirit. Dramatic victories and human
triumphs
“Not sickness but health,” a famous physician once remarked,
“is the greatest of medical mysteries.”
Your own good health is an example. Every day your body is assailed by millions
of germs, many of which can produce illness or even death. Yet you stay well. Countless bacteria and viruses gain entry
into your body with the food you eat or the air you breathe or through breaks
in your skin. Yet you stay well. Some of them establish permanent residence in
your mouth, your nose and throat, or your intestines, where they may multiply
fantastically. Yet you stay well.
What protects you from these ceaseless assaults by bacteria
and viruses?
Though decades of study scientists have been slowly finding
out. Your health is safeguarded, they
report, by an ingenious series of defenses arranged in depth like the
successive lines of an army entrenched to ward off invaders.
Suppose, for example, that a germ-laden fleck of dust floats
into your eye. In all probability there
is nothing to worry about. Your eye
surface is constantly bathed in tears, which contains a bacteria-destroying
antiseptic called lysozome. Lysozome is
so powerful tat a single teardrop diluted with half a gallon of water will
still destroy at least one species of germs.
Your saliva and other fluids manufactured by your body also
contain lysozome, as well as other antiseptic chemicals called leukins, lysine
and plains, which have not yet been fully studied. Even your bare skin has considerable
germicidal power. For example, virulent
dysentery bacteria in a drop of fluid placed on a glass slide will survive for
hours, while those in a drop placed on the clean palm of your hand will be dead
within about 20 minutes.
Some kinds of germs can survive these external defenses and
even multiply on your skin. Before they
can harm you, however, they must gain entry into your body and then run an
amazing gantlet of other defenses.
Antiseptics in your saliva, for instance, attack germs entering through
your mouth. For those that are swallowed
and washed into your stomach powerful digestive juices lie in wait. Few of the harmful bacteria reach your
intestines alive.
Germs that gain entry through your nose must thread the
complicated maze of your air-filtering nasal passages. The surfaces of these passages are kept moist
by mucous fluid that acts like flypaper in catching germs. If the germs cause
irritation, they are sneezed out; or your nose starts to run and they are
flushed out. Germs that manage to reach
the tubes to the lungs are also trapped in a mucous fluid, and are sometimes
coughed out. Tiny hairs like fibrils are
constantly waving in the mucous fluid, propelling it toward your throat. Germs trapped in the fluid and meet their
fate in the well-guarded gastrointestsstinal tract.
When germs get into your body through breaks in your skin or
mucous surfaces—breaks so small that they may be unnoticed—the peril is
seemingly greater. Let’s say that you
step on a germ-laden nail. Watch germ
thus entering your tissues may divide into two after 20 minutes. If this rate were to continue, you would be
host to a million descendents within seven hours, and they and to several
quadrillion next day. By then your
entire body would, of course, be overwhelmed.
But before this can happen another type of defense, called inflammation,
will have come to your aid.
Inflammation begins when various chemicals are released at
the site of a germ invasion by the invaders or by the injured cells in your
body. These chemicals seep outward in
all directions until they reach the nearest blood vessels. There they cause a relaxing of the vessel
walls that enables plasma, the watery part of the blood, to seep out. Accompanying the blood plasma are white cells
called leucocytes, and various chemicals that curb bacterial growth.
Leucocytes are among the most curious and most effective of
your body’s defenses. In appearance they
resemble the one-celled animal called amoeba, and like the amoeba they can
propel themselves from place to place within your body. In some way most yet understood leucocytes
are attracted as if by a magnet to the site of a bacterial invasion. When they arrive they gobble up any invading
particles they find.
It is fascinating to watch this gobbling-up process through
a microscope. A leukocyte slithers up an
invading bacterium, crowds it against a solid surface, then flows its
jelly-like body around the bacterium to “corner” it. Next it opens a b\hole in its skin-like
membrane, and the bacterium is completely engulfed. A moment later the leukocyte slithers off
after its next quarry. Millions of
leucocytes are often mobilized at the site of an infection.
Other factors involved in inflammation help the leucocytes
in their work. In blood plasma is a
chemical called fibrinogen (the chemical responsible for blood clots), which
quickly solidifies into a network of strands and, with other plasma substances
and the leucocytes, forms a wall around the battlefield, trapping the germs so
that the infection is localized. Boils and
abscesses are typical examples of how this walling-off process safeguards the
rest of your body from germ invaders.
Even though bacteria are thus contained, the resources of
your entire body are mobilized to defeat them.
Some of the chemicals released during the battle enter your blood stream
and carry the alarm to storehouses throughout your body where leucocytes
reserves and maintained. Within minutes
millions of additional leucocytes are released into your blood, which carries
them to all your tissues. While this is
going on, your bone marrow is also alerted and it speeds up the manufacture of
new leukocyte reserves.
Some germs are coated with a repellent, which keeps
leucocytes away, and some have the power to kill the leucocytes that engulf
them. Even in death, however, the
leucocytes continue to release chemical injurious to germs.
If the leucocytes cannot complete the mopping-up operation,
they are joined by larger (but still microscopic) cells called
macrophages. These can gobble up not
only bacteria but also leucocytes that are harboring bacteria.
Usually when leukocyte or macrophage engulfs a germ it means
death to the germ, but not always. Some
bacteria can survive for long periods within cells which have gobbled them up,
indeed, a cell may occasionally prolong the life of a bacterium by protecting
it from antiseptic blood substances and from the drugs your physician
prescribes to help combat the infection.
Your body requires a way to dispose of these germs after they have been
engulfed, and of other waste products.
To provide for this, a network of channels called the
lymphatic system drains your body tissues.
Leucocytes, macrophages and invading particles enter the vessels of this
network and are carried by the lymph fluid to “regional lymph nodes,” the
glands, situated at strategic points through your body. Each node serves as a filter, holding back
bacteria and other particles. The lymph
fluid flows on from one node to another until it reaches the ones in the neck,
where it is discharged into the blood stream.
By then, generally, all germs have been filtered out of the lymph fluid.
Following an illness, however, disease germs may survive for
days or even weeks within the lymph nodes.
The glands in your neck are the final barriers, which prevent germs from
reaching your blood stream, and the survival of germs in them for long periods
explains shy these glands sometimes remain swollen and tender long after other
symptoms have disappeared.
Even if a few germs reach the blood stream, another alien of
defense stands ready. Your bone marrow,
liver, spleen and a few smaller organs are equipped with multitudes of
macrophages to filter invading particles out of your blood just as the lymph
nodes filter your lymph fluid.
How ate these leucocytes and macrophages able to distinguish
between invading germs or other particles and the cells or molecules of your
own body? Your body has a built-in
identification system, which labels invading particles! These labels, which attach themselves to
invaders, are called antibodies.
Leucocytes and macrophages will occasionally engulf almost any particle
they happen upon, but the ones they search out and devour with the greatest
voracity are those, which have been labeled as invaders by antibodies.
Most cases of recovery from an infection are traceable in
large part to antibody action. If you
have ever had scarlet fever, your body lacks antibodies tailored to fit the
streptococci, which cause these diseases.
But if streptococci secure a sufficient toehold in your body to
multiply, your antibody factories start tooling up. For several days, perhaps, the germs continue
to multiply and you get sicker and sicker.
By then, however, full-scale antibody production has begun and
antibodies are turned out in large amounts.
These latches into the scarlet-fever streptococci, which as soon as they
are libellee, fall prey to the voracious leucocytes and macrophages, and your
recovery begins. Substances in your
blood called complement also help out by destroying bacteria to which
antibodies are attached.
It is chiefly your antibodies, which make you immune to
second attacks of many common illnesses.
The first time you suffer from a disease such as scarlet fever or
measles your antibody factories take several days to learn the right
pattern. Once the lesson is learned,
however, production can begin much more promptly, and large amounts of
antibodies of the desired pattern may be turned out within a few hours after
the entry of a few thousand germs. Thus
the second and subsequent invasions of a particular type of germ are frequently
wiped out before you even suspect that you’ve been infected.
Antibodies are also the agents, which make in possible to
control infectious diseases through vaccination. A vaccine is a substance, which teaches your
body in advance how to manufacture antibodies promptly against a disease you
have not yet encountered. The Salk Polio
vaccine, for instance, uses polioviruses, which have been killed by
formaldehyde to teach your body how to manufacture antibodies against living
polioviruses.
A few kinds of germs have learned how to evade our antibody
defenses. The influenza virus is the
most striking example. Every few years a
type of flu virus comes along which is unaffected by common flu
antibodies. When this happens, influenza
“pandemic” sweeps the world. Witching a
few years almost everybody gets the new kind of flu and develops antibodies
against it—and about this time a new strain of the flu viruses pops up. Each type of flu requires a separate
antibody.
Most of the antibodies circulating in your blood are found
in a part of the blood plasma called gamma globulin. This antibody-rich substance ca be extracted
from the blood of donors and stored for considerable periods. Small injections of gamma globulin will
provide temporally immunity to measles and infectious hepatitis; the “borrowed
antibodies” in the gamma globulin act just like the antibodies you manufacture
yourself.
Newborn babies also stay well on borrowed antibodies. Their antibody factories operate poorly or
not at all during the first few weeks of life, but antibodies received from
their mothers before birth protects them for a time from most of the diseases
to which the mothers themselves are immune.
Babies also get protective antibodies in mother’s milk, especially in
the milk secreted during the first few days of nursing.
Some germs attack only cells in their immediate vicinity;
others release poisonous molecules called toxins which may circulate to other
parts of the body. Diphtheria and
tetanus bacteria are examples of these toxin producers. When attacked by toxins your body
manufactures antitoxins—that is, antibodies against toxin molecules. And just as you can be immunized against virus
diseases by means of vaccines containing denatured viruses, so you can be injections
of denatured toxins called toxics.
Could mankind survive without the human body’s miraculously
coordinated “defense in depth? It seems
unlikely.
No comments:
Post a Comment