Of all the body’s sense organs, the nose gets the scanties regard. We worry about our eyes and ears – indeed, millions of people seek attention for them – but we ten to teak our noses for granted. Eyes, ears an lips are the stuff of poetry: the nose is kept to the grindstone.
Maybe all that is because nose causes so little trouble, and functions almost perfectly long after we are wearing glasses and perhaps a hearing aid. Everyday, the average nose cleans and conditions about 15 cu m (530 cu ft) of air, enough to fill a small room. Whether the day is freezing cold or fiercely hot, this neat little air conditioner delivers air at about the same temperature of 35 ° C (95 ° F) and suitably humidified, about 80 percent saturated.
Offer air conditioners are notorious for supplying bacteria-laden air. Our nostrils screen out impurities before they can reach the lungs. That is why doctors and wise parents urge children to develop the habit of breathing through the nose and not the mouth. The noses filters air in a two-part process. First, a barrier of stiff hairs just inside the nose traps larges particles of grip and pollen. If the invader is particularly offensive, it may be injected forcibly by triggering a sneeze.
Anything that beats the first defenses meets a tougher enemy, the mucous membrane, which acts like a kind of flypaper. To provide moisture for the air and a sticky mucus to coat the membrane, the nose secretes nearly a liter (about a quart) of moisture a day. The sticky mucus catches the bacteria, and kills them with an enzyme called lysozyme. This same agent protects our eyes from infection and makes breast milk so safe for infants.
To keep the flypaper fresh and sticky, the nose produces a fresh batch of mucus every twenty minutes. An army microscopic brooms – fine hairs known as cilia – poke through the mucus coating and, the old mucus coating and, with up to 1,000 strokes a minute, sweep the old mucus to the throat. The debris goes into the stomach, where digestive juices destroy out of the bacteria.
Normally, the cillia keep the mucus moving at about 6 mm (1/4 in) in a minute. Smoking and drinking alcohol to excess will slow down the flow, weakening the body’s defenses against airborne disease.
In addition to its major role as an air conditioner, the nose gives the voice resonance. And it identifies a smell – on average, about 4,000 different scents. A really sensitive nose, developed often by somebody born blind and deaf, can detect some 10,000 separate odors.