How Your Body Keeps You Well
By RUTH and DEWARD BRECHER
“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.
