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.
