Aromatherapy involved inhaling pleasant smells and is a non-medicinal form of treatment for various psychological disorders. A nice smell triggers hormones of happiness (serotonin, dopamine, oxytocin, and endorphin) and helps overcome depression by stimulating the brain. A smell disorder is a malfunction that might even indicate neurological and psychological illnesses. One of the most crucial parts of the brain that is impacted by Parkinson’s or Alzheimer’s is the region that specializes in sense of smell. We mostly fail to notice what a blessing it is to be able to smell until we lose it. Otherwise, we are exposed to thousands of different smells every day.

Even minor issues with the nose can cause major inconveniences. Nasal congestion lessens the quality of everyday life: it is hard to sleep with a congested nose; even if you manage to fall sleep, the quality of sleep drops significantly.

The magnificent functions of the nose are as follows:

1. Sense of smell enables us to identify beneficial and harmful things and keep away from harmful ones. The nose helps spread the feeling of peace and happiness produced by nice smells that influence the spirit through the brain (olfaction).
2. The nose helps protect the respiratory passage from diseases by moistening and heating the inhaled air as it is carried to the lungs and cleaning foreign objects from the lungs with the mucus it secretes (inspiration and regulation).
3. It regulates the resonance of sound vibrations formed in the vocal cords, thereby virtually acting as loudspeakers (phonation).

These functions are miraculous, and yet we never contemplate them or their perfect engineering.

The nose: our body’s air-conditioning device

Before inhaled air reaches our lungs, it passes a turbulent current through the nose, which is by all means a perfect air-conditioning device and air filter.

Air that enters the nasal cavities through the nostrils flows through inner nasal canals to the nasopharynx (upper-frontal pharynx). It then flows down the pharynx to the larynx and finally to the lungs. Inside the nostrils are hairs that trap and filter dust, sand, pollen, and little bugs. Cleaned of these particles, air then passes through canals (meatus), which are anatomical engineering wonders in each nostril, and over turbinal structures (conchae) (Figure 1).

The exterior of these scroll-shaped canals in the nasal cavity are lined with a moist layer that secretes the fluid called mucus. Thanks to the magnificent architecture of the air conditioning chimney made up of these canals and folds, particles of dust are retained by this mucosa membrane. On this membrane there are also thin hairs (cilia) which constantly wave to and fro. This movement carries particles of dust not toward the lungs but toward the nostrils, which are then expelled when the person sneezes or blows the nose. If it were not for this precisely built structure, the inhaled air would directly go to the lungs without undergoing cleaning.

The inner working of the nose also heat or cool air, as necessary. The mucosa that lines the inside of the nose is rich in capillaries and mucus secretion. As inhaled air travels through the nose, it both warms up by absorbing heat from the blood in the mucosa veins and gains moisture by absorbing it from the mucosa. For example, when a person inhales through air from a room where the temperature is 20-22°C (68-71°F), the air heats up to 32-35°C (89-95°F) and becomes 95-98% moist by the time it reaches the larynx. If the same person breathes in through the mouth in the same room, the inhaled air can warm only up to 28–30°C (82-86°F) and reach a moisture point of 80-85%.

Without the nose, air would not be heated, moistened, and purified. The dusty, dirty, or cold air we inhale would directly go to the lungs, which would cause frequent illnesses in them and the upper respiratory tract.

How do we smell?

The nose is created with the ability to distinguish about ten thousand different smells. Its magnificent architecture is a perfect means of transport that facilitates the sense of smell in our brain, which is the real center of smell in our body. As this sense of smell function in our body, we take pleasure out of it in our soul.

The “smell molecules” communicated through the air first reach the receptors in the “olfactory epithelium” in the upper region of the nose that is equipped with a multitude of nerve cells. The stimulus that is converted into an electrical signal in this epithelium is conveyed to the smell center in the brain through olfactory nerves (Figure 2). All this process the smell molecules go through in the nose and the brain interact and impact with our soul in such a subtle way that we take delight and even be healed.

The sense of smell in certain animals (especially in dogs, moths, and some fish species) is hundreds of times more sensitive than in humans. For these animals, it is crucial for finding food and their survival.

The inability to perceive smells, or “smell blindness” (also called “anomia” in medicine), can be temporary or permanent depending on the underlying factor. Anomia is usually temporary in cases of the flu, cold, bad sinus congestion, or allergies. A decrease in olfactory sensitivity (hyposmia) can also be caused by nasal congestion, enlarged adenoids, nasal polyps, nasal deviations, or concha bullosa, which prevent air currents from reaching the olfactory region. The sense of smell usually recovers when these anatomical abnormalities are corrected; only in cases when duration of sinusitis is prolonged, namely when it becomes chronic, does loss of smell become permanent.

The impact of the nose on our voice quality

We can feel the effect of our nose on our voice quality, such as when the voice changes due to congestion or closing the nostrils with our fingers. Experienced physicians can immediately diagnose nasal congestion from the way a patient talks. Life is indeed an ordeal for people who cannot breathe easily through their noses.

Air cleared of germs

Nasal mucus is a slightly acidic secretion that carries an antibody called “immune globulin A” (IgA). Its slight acidity as well as the antibody in it allows the mucus to eliminate various germs, and the respiratory tracts are thus protected against perilous sources of illness.

The tiny sweeping hairs that line the interior of the nose can break down or stop working altogether because of certain germs, particularly viruses that cause the flu, filthy and dry air, sulfur dioxide, carbon monoxide, and cigarette smoke. Because nasal cleaning is disrupted, disease-inducing microorganisms can easily cause upper respiratory tract inflammation and other serious infections.

 The nose’s role in taste

Smell is crucial for a better perception of taste. Indeed, when there is a problem with the function of smell, a person’s sense of taste suffers, too. Nice smells have a favorable impact on the sense of smell. If we could not detect the bad smell of a rotten, harmful food item, we would not be able to stop ourselves from eating it and harming our body.

The importance of smell is highlighted in religious traditions. It is reported that the Prophet Muhammad, peace be upon him, mentioned putting on pleasant perfumes among other things that were the traditions of the messengers of God. Clippings from mush, camphor, amber or aloeswood were also burnt in the Prophet’s home for their pleasant scents.

Humans rarely consider their sense of smell. In fact, we tend to take it for granted. But through the nose’s perfect design, we are to smell and taste so much of the world around us, which is surely an everyday miracle.

Figure 1: The magnificent design of the anatomy of the nose

Figure 2: The awe-inspiring structure of the olfactory region

The oral cavity is one of the many systems that is perfectly designed while a fetus develops in a mother’s womb

The first event that takes place inside the mother’s womb is the union of sperm and egg to form into a single cell which later takes the shape of an embryo by rapid division and development. This embryological development occurs in three stages.

In the first of these stages (2-5 weeks), the fertilized egg (zygote) proliferates by dividing and planting itself to the womb wall (implantation). During the advance of the zygote towards the womb, some biochemical signals are sent in order to make the mother sense this situation. Via these signals, the mother’s body is prepared to supply the necessary nutrients to this cellular mass. When these biochemical signals reach the ovaries, various hormones are secreted and the ovulation that occurs during monthly periods is ceased.

During the second stage (5-6 weeks), major activities are started inside the cellular mass, which is now in the form of an embryo. The developmental process of organ and system generation from cells begins.

And during the third stage (from the 8^th week until birth), the embryo has become a fetus, and its facial and bodily structures have begun to be immaculately shaped (Figure-1).

How do organs develop?

Tissues and organs of the embryo, which morphologically starts to look like a human, develop from three layers, which are called the ectoderm, mesoderm, and endoderm. While the baby continues to come to life inside the mother’s womb, the cranial and facial regions, along with oral cavity, start to form via the development of cells in the area called the neural crest. This development is the result of perfectly corresponding functions in between the epithelium and outer mesenchyme, which results in the facial skeleton and formation of teeth.

Jaw and facial development occur during the 4-12 weeks in the womb. By the end of the 10^th week, the face can be seen with an ultrasonographic examination.

The nose forms at this point. Mid and lateral nose projections develop. A forehead projection called the “frontonasal protrusion” forms in between the two sided mid nose projections. These projections initially develop towards the lower direction because of the volume of the tongue. Later, after the palate has begun to form, and with the growth of the lower jaw and the downward extension of the tongue, like an open-close bridge, the lower and upper jaw join at the midline by rising upward. This union takes place from front to back, like closing a zipper, stage by stage.

This way, the oral cavity and the surrounding structures (tongue, teeth, etc.) that will enable speech and taste are knit, loop by loop, inside the mother’s womb. (Figure 1-2)

Due to the complexity of this process, if there happens to be any failure in the merging, some anomalies can form, such as split lips or palates. These splits are anomalies present at birth. Such lip or palate splits may arise during this phase of the pregnancy because of various negative factors: they can stem from inter-family marriages, diseases that the mother experiences during the first three months of the pregnancy (especially measles or toxoplasmosis), exposure to radiation, alcohol consumption during pregnancy, or various drugs the mother uses. These anomalies need to be corrected by plastic surgeons, upper respiratory tract specialists, and orthodontists.

Despite these anomalies, most of the time, babies are born with their oral cavities in perfect working order – which is extraordinary given the complexity of the process.

Reference

Oral R. J, Goldman H.M. Thoma’s oral Pathology.The CV Mosby Comp. St. Louis.

Figure-1: Ultrasonographic image of the facial region of a fetus in the mothers womb.

Figure-2: Upper jaw bone

The dispersal of scent takes place via the thermal and light-like behavior of the fragrant particles in the air. Thousands of points, letters, and words are positioned in each and every air particle. Each molecule is created in a form to carry sounds, sights, and odor. Millions of sound waves, scents and images are being transported and translocated into each of the trillions of air particles without deforming or mixing. As our knowledge pertaining to this transport grows, new technological products that will enable the transport of odors will be offered to the service of mankind.

Our sense of smell occurs in the brain. The chemical molecules exiting a lemon peel stimulate the odor receptors in the nose, which are then transmitted to brain to be interpreted as electric signals. Our olfactory system can easily distinguish more than ten thousand scents. This has inspired scientists to design similar devices. These models are called “electronic noses.”

A series of chemical receptors are utilized in the electronic nose instead of the receptor proteins of the human nose. Each of these is designed to sense various scents. These devices are difficult to produce, as the cost grows for a more sensitive device. The signals that sensors collect from the environment are converted into binary codes via electronic systems and then sent to a computer. The role of human nerve cells in charge of sensing odor is replaced by the electronic systems of a computer.

Mostly in their early phases, electronic noses are beginning to be used in various sectors, primarily those involving foods and perfumes, as well as the medical and chemical industries.

How does odor transportation take place?

As I already mentioned, the aromatic molecules transported via air particles in their gaseous state are detected by the smell sensor system and converted into electric signals. Quite a few different materials are used as conductors: conductive polymers, semi-conductive metal oxides, a quartz-crystal micro-balance (QMB), surface acoustic wave (SAW) sensors, pellistors, and infrared sensors.

Once the electric signals are converted into binary, the odor information is determined via a software program in which algorithms such as artificial nerve networks and support vector machines are employed. This information is then transmitted to a remote medium via lines of communication, such as a computer network, the internet, or another form of mobile communication. The odor type is received in the target computer. This detection stage can be completed in the target PC when necessary.

Today’s technology can only permit the transmission of odor data. In order to perceive the transmitted information at the target location as smell, the scents must be present as stored in containers and must be triggered via received odor data to be dispersed. The research in this field is limited, with ongoing pilot studies.

How can diseases be diagnosed with odors?

The natural functions of the human body, such as sweat, blood, urine, and feces, can be used to help diagnose diseases. The odor of the gases in human breath holds significant information regarding body health. There are between two hundred and four hundred different gases found in human breath. Furthermore, the number of gas types detected and described in the breath can exceed three thousand. While blood gets cleaned in the lungs, the gases of the used blood pass to the breath via the alveoli. Therefore, many critical pieces of bodily information are present in the breath.

The gases exhaled through our breath are composed of various alkaline and aromatic compounds. Each of these is a potential indicator that provides information about a disease. The gases and their ratio in the breath of a healthy person are well established. Since the ratio of the gases in the breath gets altered depending on the cause of an illness – such as diabetes (Type I and II), cancer of the ear-nose-throat, tuberculosis, and women’s reproductive diseases – can be diagnosed by utilizing the electronic nose.

There are other uses for the technology, too. NASA is developing a highly sensitive artificial nose for space research. This device will almost be able to distinguish every type of chemical compound, making more sensitive measurements than a human nose. With this device, the detection of harmful substances in the space station will be possible.

Google has announced that significant progress has been made regarding the “Google nose” which helped revolutionize searching for aromas. The Google Aroma database (http://www.google.com.tr/intl/tr/landing/nose/) stores more than 15 million kinds of scent. The days when we will be able to smell the scent of any product through our internet based devices do not seem to be too distant. To make this possible, sound waves would be converted into odor signals. There is a partially-imaginary video prepared to show how this can feel.

New technologies will change our relationship with smell, which has always been deeply important to humanity. Reference is made of this in the Qur’an, especially when the Prophet Jacob of Canaan sensed the fragrance of his son, Joseph, who was hundreds of miles away. The verse, from the chapter of Joseph, reads, “Surely, I sense the fragrance of Joseph, unless you would consider me a dotard. “It shows how valuable scent is to us, as anyone who has had a long lost memory triggered by an unexpected smell understands. As the verse suggests, losing our sense of smell is akin to losing our minds. Research has borne this out, as one of the first symptoms of Alzheimer’s disease is the loss of smell. In fact, monitoring loss of scent has helped with the early detection and prevention of Alzheimer’s. This is yet another way that our body has been perfectly calibrated to cue us in to its messages. In this regard, as with many, technology is still trying to catch up to nature.

We have to breathe in order to live. The oxygen, which is essential for us, is cleansed and its heat and moisture are regulated as it passes turbulently down the narrow channels of the nose. Thus, the air we breathe is made ready for service to the alveolus in the lungs. In this way, approximately fifteen square meters of air, which is inhaled with 23,000 breaths daily, is processed in the nose.

The area behind the nostrils has been equipped with an acclimating system that is astonishingly sensitive and which scientists have difficulty explaining. This system not only regulates the heat and moisture of air, but at the same time, it possesses a mechanism that perceives harmful molecules in the contents of the air and gives an alarm. By stimulating the nose’s mucosa, this alarm mechanism shows activity by evacuating with the speed of a hurricane the air in the lungs via the nose and mouth-this is what we call sneezing. As a result of sneezing, the harmful matter that entered the body with the inhaled air is expelled from the body.

How and why do we sneeze?

It is a Divine blessing that we do not become ill frequently in spite of the millions of microorganisms that enter our body everyday mainly through the air we breathe. The microbes that enter our noses with the air we breathe are caught together with dust by tiny hairs here called cilia. Those that escape here are asked for a password by the anti-bacterial mucus secretion emitted by the epithelium tissues in our noses. In order for smells to be perceived by the nerve cells of molecules, the thickness of mucus must be around .06 mm. If the mucus layer were thicker, our sense of smell would be decreased, and if it were thinner, the defense system would weaken and cilia would be easily harmed. In addition, with its content and density, this secretion is responsible for filtering foreign particles in the air and for moisturizing the air to make it suitable. Because it is dangerous for things to pass this point, the body’s alarm that we call sneezing kicks in and microbes are expelled in this way. Sneezing is one of the most important defense mechanisms of the upper respiratory system. When the thresholds of the special nerve cells in the nose are stimulated, the signals reach the brain and the sneezing reflex kicks in. The mucus tissues are stimulated, mucus is secreted and the capillaries widen. Meanwhile an itching or tingling sensation is felt in the nose. As a result of the warning coming from the brain to the head, neck and stomach muscles, air is closed into the area where the vocal chords are and pressure is greatly increased in the lungs. Later, while the air is suddenly and loudly forced out, the foreign matter in the nose and respiratory path are thrown out. Because the nerves responsible for sneezing are also connected to the eyes, tears are usually secreted during sneezing and at this time the eyes involuntarily close.

In addition to the discomforts of the flu, the common cold, and bronchitis causing sneezing, external factors like nose polyps, flying pollen, dust, perfume, animal hairs and even suddenly looking at the light can also cause it. Because some people are sensitive to certain factors, they can be affected faster and they will sneeze. Some are more amenable to sneezing during certain periods. For example, it has been determined that pregnant women are more inclined to sneeze due to the hormonal change they are experiencing. It has also been established that the members of some families sneeze consecutively in certain numbers (3-5 times); this situation supports the idea that sneezing attacks can be hereditary. It is known that men sneeze more than women and that white people sneeze more than black people. One out of five people sneeze when they look at a bright light while walking in the dark. Due to the sudden reflection of light, the pupil of the eye contracts and the emission of tears increase. This emission reaches the upper division of the nose cavity by means of the tear ducts and, stimulating the mucus tissue in the nose, it triggers sneezing. In illnesses such as the common cold, the mucus in the nose quickly triggers sneezing because it is more sensitive.

Beware of cluster bombs

Sneezing is one of the rare moments when the body desires a situation different from its normal functioning. Sneezing and coughing lead to a movement of air strong enough to break the mucus bond, and as a result, droplets are formed. It has been established that the speed of air and the particles in it while being expelled from the mouth at this time is close to 100 miles per hour. Those who carry the viruses of illnesses like the flu scatter about close to one hundred million microorganisms during sneezing-like a cluster bomb. From 2,500–5,000 droplet seeds can remain in the air for hours in the cloudlet that has been formed. As the diameter of the droplet seeds decreases, their period of staying in the air increases. The diameter of droplet seeds that remain in the air for a long time and cause the spread of illnesses is between one and five microns.

Rather than food and drink, tuberculosis spreads by deep respiratory movements like sneezing and coughing via droplets loaded with bacillus. Dispersing in the air into smaller particles, the droplets are inhaled by healthy people by means of the respiratory path.

If necessary precautions are not taken in regard to a viral infection, it can spread throughout the world in one month, because the droplets carrying the virus can travel forty meters when you sneeze, six meters when you cough, and two meters when you talk. For this reason, illnesses like the flu which spread with droplets are frequently seen during the winter. For one person sneezing several times in places where there are crowds of people means that the virus spreads to hundreds of people within a few minutes.

Is sneezing beneficial?

The movement of cilia in the upper respiratory path is very important in regard to the health of the lungs. They hold the harmful matter coming with the air, trigger the sneezing reflex, and together with mucus, prevent them from entering the lungs, thus performing a very important protective duty. The expulsion from the body of matter that is probably harmful together with the air in the lungs is a blessing that provides a person with a great benefit. Consequently, formerly natural powders like black pepper known as snuff were breathed into the nose in order to sneeze. While sneezing, the brain and cardiovascular veins expand and tear and sinus ducts open; thus, the dead air we normally cannot exhale is forced from our lungs.

When sneezing, a high amount of pressure is generated in the body, especially in the stomach area and brain. Due to this pressure, a lot of blood goes to the cardiovascular veins, and in fact, serious situations like fainting can occur during sneezing attacks. However, sneezing is beneficial to a healthy heart. Fully closing the mouth and holding the breath while sneezing can bring about bursting and tearing in the lungs. The ribs can even break with an intense and unbalanced sneeze. If a person tries to stifle the sneeze after the sneeze reflex has occurred by closing his mouth and nose, he can harm the brain and bring on paralysis or when the pressure increases in the capillaries in the brain, bleeding can occur. In this situation, people, especially those who have undergone an operation, can be seriously harmed. In addition, veins in the eyes can expand and rupture. When sneezing is triggered, a person should relax and not prevent the sneeze.

In addition to providing protection against harmful things that have entered the respiratory system, sneezing is a reflex that is a means for relaxation, relief and invigoration of the body. If this reflex had not been put in the body, it would be difficult to escape many harmful things that would give discomfort. During sneezing, the rest period after diastole of the heart increases. This is probably the reason why we say, “Bless you” when someone sneezes. Prophet Muhammad, peace and blessings be upon him, said, “One of the six rights of a believer over another is to make a prayer when he or she sneezes,” and “One of the times when prayer is accepted is at the moment of sneezing.” It was related that the Prophet, peace and blessings be upon him, “covered his face with his hands or a cloth when he sneezed and he lowered his voice.”

We are being reminded of the value of our health which God bestows upon us anew each time we sneeze. Sneezing is a cloud of mercy not only for us, but also for those who witness this moment with prayer and with whom we share feelings of gratitude.

Adem Arikanli is a freelance writer from Turkey with an interest in health and biology.

I have been positioned in the center of your face so masterfully and delicately that even my slightest displacement would cause your face to become disfigured immediately. You would lose your good looks if I were wounded or spoiled. It seems to me that after creating your whole face and body, God placed me very accurately so that I can be in perfect harmony with them, and even with your soul. We noses appear in countless shapes-slender, long, narrow, wide, flat, Roman (convex), sharp and stubby noses. In the past, some wise men used to comment on people’s personality by looking at the posture and shape of their faces and bodies. The different shapes of noses would give them ideas about the intelligence and the will power of each person. It is true that there is a relationship between my shape and your personality. However, it would be wrong for someone to claim to know all about you just by looking at my shape, since your other organs affect one another too; some can neutralize the effects of others. Moreover, discipline and education can change many of the characteristics of a person. So, do not judge people just by looking at their nose.

Anyway, since these are subjective matters, they are not our focus now. What I would like to tell you about is the objective truth about the delicate art and meaning in my creation. My Creator has designed me as a projecting organ on the head-and not only on your face, but also all vertebrate animals, especially mammals. I am the organ that is used most by animals to hunt for food, to feed, and to look for their young or their mate. I am placed at the front of your body, and like a detector I sensitively recognize smells. When animals find something new, they first poke me into it to understand what it is. That is why the idiom “to poke your nose into something” is used commonly among humans, meaning to interfere with something that does not concern one. Most animals use the sense of smell more than humans do. Since they do not possess the intelligence and consciousness of humans, they acquire some of the necessary knowledge to survive through their sense of smell. However, humans are given intelligence and consciousness, and so they are not supposed to “poke their nose” into everything. Of course, that does not mean that I am useless. On the contrary, I have many functions and a complex and meaningful structure.

In the middle of your face is my external component, which is shaped like a pyramid. Because it is made of cartilage, this part is quite flexible. My tip is beaked and there are plates on my two sides. The cartilage in my tip is connected to a bone in my upper part between your eye sockets. This bone, called the nasal bone, is a part of the main bone of the forehead. A cartilaginous bridge that is lined in the middle divides my nasal cavity into two nostrils which lead to the outside. The hard palate at my base also makes up the roof of your mouth. The soft palate that is behind this extends to the nasal portion of the throat (nasopharynx). During the act of swallowing, it rises and closes off the upper pharynx to prevent food and saliva from escaping from your throat and being forced up into my back. If, when eating, you feel tickling in your throat and cough, this palate cannot close off, and the food can lodge in me and come out of my nostrils. Another benefit of this system can be seen in patients and those who are about to have surgery, when their pharynx is closed off. In such situations, patients are provided with food, liquids and air via a tube which runs through me.

The journey of the air you breathe, which you have to do in order to survive, starts with me and continues as far as your lungs. The air that enters through my nostrils is not always clean and of good enough quality to enter your lungs. If low-quality air reaches your lungs, you will get cold, infected, and sick. To protect you from that, our All-knowing God created everything carefully, taking measures to ensure your well being. He has placed air-filtering hairs at the front part of my cavity, and He has covered the inner surface of my rear with a mucous membrane (mucosa) that has a fluid form. The structure of my cavity is quite complex. Along with my two lateral walls, there are three horizontal bone shelves called the concha (or the turbinate), comprising the inferior, the middle and the superior turbinates. These narrow, shell-like structures increase the surface area of my cavity and thus help to warm and humidify the air easily before it reaches the lungs. That is, the air you inhale does not pass to your lungs until it is conditioned and filtered by me. This process is initiated by the hair in my front part, which prevents the entry of dust particles. Then, the air passes through the curled aperture formed by the concha. The concha is covered by a sticky mucous membrane which produces a secretion. This slippery secretion, along with the cilia, traps smaller foreign particles such as the dust of coal, soot, bacteria or pollen. In addition to that, since the pressure inside me is lower than the pressure outside, I can easily warm and humidify the air that passes through me.

The sides and the surface of my superior concha are lined with a very special epithelium which has a role in the sense of smell. The smell receptors, which are the cilia cells, and other supporting cells constitute the olfactory epithelium for smell. Everything that releases molecules into the air has a smell of its own. Perception of a smell occurs in the brain as a result of a very complex chain of reactions. Indeed, I have no idea about how this process happens but people talk about several theories. Since the vibration and the structure of every molecule which reaches me through the air currents differ from every other, each molecule causes different chemical reactions and electrical impulses. The molecules that come through the air dissolve in the moisture which lies on my epithelium and they chemically stimulate the cells for smell. If my mucosa dries out and loses all its moisture in dry air, it becomes more difficult for the molecules to dissolve and for you to breathe. My sense of smell also weakens or gets lost in the event of a lack of the element of zinc, which normally exists in small amounts in your body.

There is a reason why the color, taste and smell of garlic are different than that of a rose or jasmine flower: it is because each creature is created out of different compounds, as if in a laboratory of its own. Therefore, the molecules that spread into the air from those different compounds and the impact they cause will naturally be different. Indeed, what is interesting here is the wonderful system which perceives each of the molecules of so many different compositions as a different smell, categorizes it, and stores its information in memory. Whenever I experience a new smell, by its composition and vibrations, I instantly figure out its difference from other smells. Then, I help to store it in the brain’s memory related to the smell so that I can recognize that smell if I come across it again. All of those functions in their complexity remain an enigma which is still being studied by physiologists of smell. Another wonderful attribute of my smell-receptor cells is the fact that they sense the smell very strongly at first and after a while, they are not as strongly stimulated as before, resulting in a temporary paralysis of those cells. Thus, a situation called “habituation” occurs, and this is an indication of God’s mercy. If God had not created this “fading” of constantly existing smells, the sewage, garbage, tannery or butchery workers would not be able to do their work.

The mucosa that lines my cavity can easily become swollen with blood and tissue liquids. During viral or bacterial infection, or an allergy like hay fever, my cavity might become blocked completely, which makes it hard for you to breathe. Infection of your upper respiratory tract causes me to run and get blocked. You know how stagnant water gets smelly and swampy, whereas running water does not hold dirt. Similarly, when I get blocked, bacteria reproduce very fast and get transmitted to other respiratory organs. That is why, when you catch cold, you must do your best to prevent my getting blocked. Hot, aromatic or spiced teas might help you, but the best thing is to pour a weak solution of saline (salt water) into your nostrils, which will clear the congestion. As for nasal drops, do not use them unless you have to, since they will cause addiction and other side effects.

Your skull also contains four major pairs of air-filled cavities (sinuses) at my sides behind your cheeks and above me behind the forehead. In the event of infection of your sinuses, inflammation of your tonsils, or the growth of polyps, my discharge becomes constant and turns into flu or chronic rhinitis. Besides that, if I bleed it may be an important first symptom of many illnesses. Many conditions, including high blood pressure and several illnesses with fever cause bleeding inside me. Indeed, bleeding from me in patients with high blood pressure can be seen as a warning and protection against serious conditions. If, because of high blood pressure, my blood vessel did not split, bleed and decrease the pressure, a vessel in your brain would split, which would result in a much worse scenario.

Peter, from now on, do not ever forget to give thanks to God when you smell a flower or anything else with a beautiful scent. Inhale the air deeply with the pleasant impression the scent leaves on your soul. Our Lord God Almighty, who has given you the air as a blessing, bestowed you with me as a filter to clean the harmful particles from that air. If He had not done so, your lungs would fill with soot and dust and they would fail eventually. You would not be able to sense the taste of food because the experience of flavor cannot be achieved by the taste buds alone. It is me that helps them to do that. For instance, a person whose olfactory epithelium has been ruined cannot tell whether it is an apple or a radish that he or she is eating. If you cannot sense the odor of the foods you eat, you will not be able to get their flavor, either.

Dear Peter, I think I have described myself to you sufficiently. I even support your spectacles for you! I have given you brief information without too much detail about my microscopic intricacies. While even one hair inside me cannot be placed by itself, do you think it is possible for me to have formed myself when I am equipped with thousands of intricate elements, each with a reason? Which sculptor, do you think, can make the nose of a sculpture, without a hammer and chisel in his hands and without a model and will in his mind? Other than the belief in God, there is no way of explaining my creation, which is a thousand times more splendid than the making of the nose of a sculpture. So, whenever you wash your face and look into the mirror, examine me carefully again and remember our God Almighty who created us out of nothing.

Irfan Yilmaz is a professor of biology at Dokuz Eylul University, Izmir, Turkey.

I am placed inside your chest cavity as two air sacks-or bellows-surrounded by your muscles. I took my first breath right after birth and I still keep working non-stop. Even while you are sleeping, I fulfill my function with the automatic command I receive from the respiratory center at the back of your brain. My close friend Heart started working even before me while you were in the womb. I was resting then; actually I hadn’t even formed fully. As all your needs like food and oxygen were met in the body of your mother-whose heart you occasionally break-I didn’t have to make extra effort to get air, being filled and emptied. Even if I had attempted to do so, I would have had no chance of succeeding; since you were contained in the amniotic fluid, an attempt to breathe could have caused you to drown.

The first breath I take after birth is critical and rather difficult, since the windpipe is still much narrower than normal. On the other hand, the number of my alveoli where oxygen exchange with the capillaries is realized is so high in relation to body size that it balances the situation. When I make my first move and fill with air, I put pressure on the arteries and veins. Then the vessel directly connecting my artery to my mother’s aorta is dismissed, the curtain between the valves is closed and the blood circulations are separated. If this curtain is not properly closed and a gap remains in between, the oxygen-rich blood and the used-up blood mix and result in the disease known as cyanosis-or “blue baby” syndrome. As these two kinds of blood mix, the tissues are not supplied with sufficient oxygen and the white parts of the skin and eyes assume a bluish appearance.

Turning blue-purple due to lack of oxygen in the tissues is the same for smokers. Cigarettes-my archenemy-contain hundreds of toxic substances, such as carbon monoxide, which combine with the hemoglobin in blood and prevent oxygen transfer. Therefore, the lips of smokers turn slightly purple. You need to be careful with the air you inhale. The windpipe which brings air into me is covered with a ciliated epithelial tissue which catches the dust brought along and sweeps it outside. While you are asleep, the vibrating cilia of this sweeper work throughout the night and in the morning you get rid of the outcome of their propulsion by clearing your throat. However, every draw of a smoker kills 800–1,000 of our ciliated epithelial cells. After some time, they become unable to sweep the toxins (carbon, sulfur, lead, etc) inhaled with the air. I can’t stand it anymore! The increased air pollution is already putting enough strain on us… this habit is just too much for a lung to handle! It is just… an open invitation for cancer! Sorry, Peter, I didn’t mean to be rude. I appreciate that you don’t smoke, but I wish those who do would realize how splendid a mechanism they are destroying.

Now let me tell you about what a work of art I am. As you also know, art in a structure becomes more meaningful with functionality. As is the case with my other friends with which I work in your body, I am perfectly made to fulfill my duty. In other words, never mind forming an organ like me as a consequence of molecules and cells accidentally coming together, even a single protein molecule in my structure does not come to existence through unconscious causes.

With every breath you take, the pressure of the oxygen within the air inhaled rises, so it passes through my membranes by diffusion and into the adjacent capillaries; there it combines with hemoglobin molecules. At the same time, the carbon dioxide passes through the same membranes into me, and I dispose of it. Both of these are easier said than done! You breathe 13–14 times a minute and the whole thing is repeated over and over. As I keep expanding and contracting during breathing, which you are unaware of most of the time, first of all I need to be very flexible. Together with this flexibility, my most important quality is having the largest possible surface area within the smallest volume. My surface area of around 100m2 (as large as a tennis court) is made to fit into your chest cavity in the form of thin membranes so that my large surface allows gas diffusion. These membranes need to be kept wet; a special fluid is secreted as a precaution and respiration is realized smoothly. Without this fluid, my membranes would just stick together, unable to carry out their duty.

You can compare the course of the air inhaled to that of a car passing from a highway onto increasingly smaller roads and in the end reaching a dead end in the small sacks named alveoli. The air coming in through the mouth and nose unites at the expressway named the trachea, or the windpipe, which is 15cm long and 2–3cm in diameter. Incidentally, I have a couple of things to tell you about the way you breathe. As a matter of fact, inhaling is the duty of the nose. I’m sure it also has a lot to say as well, but let me just mention a simple fact about it. Now, you should inhale through your nose, so that the air you take in gets warm, wet, and is cleaned from dust. If you try to breathe this way, you do not trouble me much, and reduce the risk of catching a cold or an infection of upper respiratory system. Inhaling through the mouth helps dust and germs get into me and you might contract various illnesses from bronchitis to pneumonia. Now you know why kids who have adenoids who sleep with their mouth open get ill so easily. Sorry, I couldn’t help speaking on behalf on the nose.

Well, what were we talking about before that? Oh yes! The ways through which the inhaled air passes. As the name suggests, the windpipe which makes the air reach me is a cylindrical tube surrounded by 16–20 cartilaginous rings. As it is placed beside the esophagus, one side of the rings is made of soft cartilaginous tissue instead of hard, so that they don’t hinder swallowing. The muscular tissue near these rings helps them widen and narrow during respiration or coughing. I sometimes warn you by making you cough. Maybe it seems to be a disturbance, but if I don’t push out air by coughing through the contracted windpipe, contaminants can clog me up and cause you to suffocate. Therefore, the burst of air-what you call a cough-is a great blessing to you.

The sound system at the tip of the windpipe is another wonder. The used air I send out vibrates the cords in that voice-box and produces such melodies, gives voice to such speech! The air divides into the two lungs. My two sides are not symmetrical; the one on the right is divided into three, and the one on the left into two. I think this was meant to make room for the neighbor on the left, the heart. In addition, if there’s any cancer growth in me, the diseased part can be taken out by an operation and I can keep on functioning. God knows the wisdom behind this form. After that, these main bronchi separate into 8–10 thinner branches, like highways connecting to narrower roads. This branching resembles a tree turned upside down. At the tips of these thin branches are the respiratory bronchioles resembling clusters of grapes. The small spheres which make up the cluster are the end of the road and are the most vital parts. These spheres named alveoli are made of very thin membrane and they are surrounded by a net of capillaries (picture 5). These are the functional spots where gas exchange is realized.

I hang in the thorax with veins and arteries all around. There are two layers of protective membrane over me. One of them is stuck on me, whereas the other is stuck on the ribs which form the chest cavity. There is a fine and slippery fluid in between these two layers and it neutralizes the friction every time I inflate and deflate. If it hadn’t been placed there, I would wear out and be damaged. As I inflate during inhalation, the chest cavity should expand simultaneously to make space for me. If it weren’t given a flexible form, I would fail to breathe and you would eventually die. Fortunately, the protective set of ribs and their connection with the spine are flexible enough to make me work comfortably. In addition, the dome-shaped muscular partition (diaphragm) separating the thorax from the abdomen contracts and pushes down the organs in the abdomen. Thanks to the simultaneously programmed movement of both the ribs and the diaphragm I inflate with air and expand.

Being in constant contact with the outer environment makes me susceptible to various diseases. Coughing is among the foremost signals I give in the case of disease, and sometimes-excuse me-I produce a mixture of blood and phlegm. Also, I may have difficulty in breathing and warn you with chest pain. You should be alert to my signals. If bacteria and viruses infect me, they might reproduce inside my air sacs, and cause stiffening and suppuration.

I am particularly sensitive to allergic disorders. When the straight muscles on the walls of my bronchi contact an alien substance, pollens for instance, the consequent histamine secretion makes my muscles contract. In addition, allergic diseases, which can affect blood vessels, affect me a lot since I happen to be one of the major organs contributing to blood circulation. As a result of the contraction of my bronchial muscles and difficulty in disposing of the mucus I secrete to defend myself, I have trouble with breathing-you call it asthma.

In addition to this, we can mention diseases like emphysema, acute or chronic bronchitis as problems I frequently face. Even your anger has a great impact on me. Breathing becomes more difficult immediately.

Peter, I’m sorry, it is not possible to summarize a work of art like me within a few pages, but I need to stop now… but please, keep away from polluted areas and cigarette smoke! Send me as much fresh air as you can. And even though you mostly take me for granted, like my other teammates, please reflect upon what a blessing I am.

Irfan Yilmaz is a professor of biology at Dokuz Eylül University, Izmir, Turkey.

New Findings in Biology

Olfaction was long considered a uniquely mammalian trait. Scientists have disproven this by showing that many intertebrates can smell. For example, birds were thought to be unable to smell, although they have nostrils in their bills. John Audubon, a famous nineteenth-century bird artist, reached this mistaken conclusion by observing vultures confronted with a covered and an uncovered animal corpse, he concluded that they could not smell. The minute weight of the birds’ olfactory bulb consolidated this widespread misconception. Recent research shows that birds use smell when finding and distinguishing food, choosing proper nesting sites and mates, and following avian navigation routes. Ken Stager, an orinthogist at Los Angeles County Natural History Museum, used turkey vultures to disprove Audubon’s vulture experiment. Marine biologist Betsy Bang, who measured the olfactory bulbs and tissues in the brains of 151 bird species, calculated the olfactory bulb’s mass as being between 3% to 37% of the brain’s entire mass. This shows that the ratio, and not the weight, determines a bird’s ability to smell.

Other examples are as follows:

•Pigeons perceive small amounts of odorants. If their olfactory bulbs are blocked, they become lost.

•Certain seabirds (e.g., white chinned petrels) are sensitive to the chemical emitted by their main food (plankton), and so follow an olfactory path over the sea.

•European starlings smell the best region for their nesting site.

•Chickens detect inedible bugs (e.g., bright-colored bad-tasting caterpillars) through smell and sight.

•Salmon return to their hatching sites years later by using the unique olfactory memory of these sites left in their brains.

Smelling is far more developed in mammals, especially dogs and cats, which can sense parts per billion or trillion and can identify millions of different odorants. Science would benefit greatly if such abilities could be reproduced in sensors. But first, how does the human nose smell?

Perceiving Odors

Scientists divide human olfaction into steps. First, a potential odorant emits an odor’s basic elements: volatile organic compounds (VOCs). We perceive an odor when molecules are transformed into an odor by binding the receptor proteins.(1) After binding with certain types of VOCs, these receptor proteins cause depolarization. The electrical charges produce unique signals, which the epithelium’s sensory cells transmit to our neural network (axons).

These signals then are carried to a cluster of neural networks in the brain (glomeruli).(2) Ultimately, the impulse reaches the hypothalamus and describes the scent through a process of classification and identification.

Quantifying Scents

Human odor panels or gas chromatography and mass spectroscopy (GC/MS) are used to identify odors. Such quantification is problematic, however, because it is hard to quantify the VOC’s perception in the nose as a unit of odor. Quantifying mass, volume, temperature, light intensity, and the molecular concentration of a soluble substance in a solution are reasonably objective and can be measured as a multiple of a standard unit.

But a standard olfactory measure does not exist, for it varies according to time and environment. Odor concentration is expressed as a multiple of a threshold: 50% of human “sniffers” must detect-not necessarily identify-it. This threshold is defined by the American Society for Testing and Materials (ASTM), and is accepted as the absolute threshold of odor perception. It takes 5 or 10 odor units for the human panel to identify the odor. GC/MS also can identify the odor’s chemical composition.

Electronic Nose

After developments in electronic sight and hearing, scientists sought similar progress in odor perception. Research began at the University of Warwick (Coventry, England) in the 1980s. Its participants coined the term “electronic nose,” now commonly known as “e-nose.”(3) Their progress made it a commercial commodity with many applications.

E-noses have moved from being metal oxide devices, to conducting polymers, and now to laptop-size or pocket-size odor sensors. The Swiss Federal Institute of Technology (Zurich) has made one the size of a wrist-watch. However, current e-nose use is largely restricted to labs and military applications. Scientists are trying to match or surpass the human sense of smell’s accuracy and sensitivity, after which they will work on surpassing that of the canine species.

Uses and Advantages

E-noses have a wide application in agriculture. Since they can detect minute differences, an e-nose using polymer materials can determine whether a tomato is sun-ripened, picked green, or internally damaged, and whether apple juice comes from a concentrate or is authentic but pasteurized.

Volunteers often test such products. But who wants to determine if corn oil is rancid or canola oil is oxidized? E-noses, having no such “qualms,” detect changed odors in oil samples and provide far more accurate reports.

In animal science and poultry, e-noses provide detailed reports about spoiled food. Judy Arnold, a microbiologist in Athens, GA, researches food quality for the Agricultural Research Service (ARS).

In 1998, researchers discovered that e-noses can detect gases produced by spoiled poultry products. They claim that an e-nose can determine freshness, period of time in a refrigerator, and the amount of fat in white meat. Such an objective evaluation benefits poultry farmers and producers by eliminating returns of “funny-smelling” poultry. E-noses also can detect meat’s decay rate and bacteria, overall quality and freshness, the composition of mixed meat-part products (e.g., processed meat), and how long a ham has been dry-cured. Given this, the e-nose’s ability to examine a bundle of scents makes it very useful. It can perform hundreds of preliminary assessments that would occupy a chemist for months.

The military uses e-noses to detect land mines and traces of chemical-biological weapons. This is important, for over 100 million land mines litter 62 war-torn countries. Although dog-sniffers are useful, this practice is inhumane (dogs are often injured) and impractical (they need lots of training).

E-noses also are better than metal detectors and ground-penetrating radar and infrared imaging-the former detects even tiny pieces of metal, whereas the latter often images pebbles. As e-noses can identify traces of TNT or similar explosives to the 100 parts per quadrillion level, their detection rate is far more accurate and efficient. Nomadics, a Still-water, OK-based company, produces a cigar-box-sized e-nose for this purpose. Tufts University produces an optical e-nose that is designed and functions much like a mammalian nose.

Environmentalists use e-noses to analyze air. For instance, e-noses can report the chemical makeup of odors emitted by a farm’s store of manure, detect the compounds causing that odor, help minimize leaks, and determine a new diet that will decrease such odors. With their ability to detect toxic VOCs and compounds leaking from a factory’s or waste site’s storage areas, e-noses will help environmentalists force industry to change its practices. The major difficulty here remains sampling, as concentrations vary with time and place.

Caltech has used Department of Defense funding to develop a device that identifies odors in seconds. Its 32 components swell like sponges when exposed to a particular vapor, and its resistance (hence conductivity) changes accordingly. As it can detect any type of odor, doctors at the Children’s Hospital in Los Angeles are studying medical applications. Currently, it is applied to patients’ breath to help diagnose upper respiratory infections.

The major advantages of e-noses over human noses in these areas are objectivity; ability to measure odors over long real-time periods; and immunity to fatigue, infection, mental state, hazardous material, and adaptation (gradual loss of sensitivity).

How E-noses Work

E-noses have three functional components: a sample handler, a gas sensor array, and a signal processing system. Its output identifies the odorant, estimates its concentration, and relates its characteristic properties. A sensor recognizes different types and concentrations of odors through its arrays, each of which has a different sensitivity. The resulting combination provides the response pattern that enables the e-nose to identify odorants.

In a typical e-nose, a vacuum pump pulls the first air sample into the tube housing the electronic sensor arrays. The air sampling unit exposes the odorant to the sensor, after which VOCs interact with the surface and the sensor’s active material until reaching a steady state. The sensor’s response is recorded and transmitted to the signal-processing unit. When completed, a washing gas cleanses the sensor. After the reference gas is applied to the unit, the sensor is ready to measure again.

E-nose Technologies

The sensor is the e-nose’s key element, and the sensor type is its defining characteristic. There are 5 types of e-nose sensors, as follows:

Optical sensors: Optical fiber sensors work through fluorescence and chemoluminescence. The tube’s glass fibers contain a thin encoated active material in their sides and at both ends. As VOCs interact with the organic matrix’s chemical dyes, the dye’s fluorescent emission changes the spectrum. These changes then are measured and recorded for different odorous particles.

Fiber arrays with different dye mixtures can be used as sensors. These are fabricated by dipcoating (binding a plastic solution to a substrate), micro electromechanical system (MEMS), and precision machining. The main advantage is that this adjustable tool can filter out noise. Also, since many dye forms are available in biological research, sensors are cheap and easy to fabricate. But the instrumentation control systems are complex, which adds to the cost, and have a limited lifetime due to photo bleaching (the sensing process slowly consumes the fluorescent dyes).

Optical sensors are sensitive and can measure low ppb (parts per billion); however, they are still in the researach stage of development.

Spectrometry-based Sensors: This group consists of a molecular spectrum-based gas chromatography (GC), an atomic mass spectrum-based mass spectrometry (MS), and a transmitted light spectrum-based light spectrum (LS). The first two can analyze the odor’s components accurately, which is a plus. However, their use of a vapor trap to increase concentration can alter the odor’s characteristics. LS devices do not consume the sample, but do require tunable quantum-well devices. GC and MS devices are commercially available, while LS devices are only at the research stage. All spectrometry-based sensors are fabricated by MEMS and precision machining, and can measure odors to a low ppb level.

The GC tube decomposes the odorant into its molecular constituents, and MS forms a mass spectrum for each peak. The spectra then is compared to a large precompiled database of spectral peaks to classify and identify odorants.

MOSFET (Metal-oxide-silicon field-effect-transistor): The basic principle here is capacitive charge coupling. In other words, VOCs react with the catalytic metal and thereby alter the device’s electrical properties. The device’s selectivity and sensitivity can be fine-tuned by varying the metal catalyst’s thickness and composition. MOSFETs are micro-fabricated and commercially available, but can measure only parts per million. They can be manufactured by electronic interface circuits, which minimizes batch-to-batch variation. However, the gas produced by the VOC-metal reaction must penetrate the MOSFET’s gate.

Conductivity Sensors: The sensor types used here are metal oxide or conducting polymer. Both operate on the principle of conductivity, for their resistance changes as they interact with VOCs. Metal oxide sensors are common, commercially available, inexpensive, and easy to produce (they are micro-fabricated). Their sensitivity ranges from 5-500 ppm. However, they only operate at high temperatures (200°C to 400°C).

In conducting polymer sensors, VOCs bond with the polymer backbone and change the polymer’s conductivity (resistance). They are micro-fabricated together with electroplating and screen printing, are commercially available, and can measure from .1 to 100 ppm. They operate at room temperature, yet are very sensitive to humidity. Moreover, it is hard to electropolymerize the active material, which makes batch-to-batch variation inevitable. Sometimes VOCs penetrate the polymer chain, which means that the sensor must be returned to its neutral and reference state-a very time-consuming process.

Piezoelectric Sensors: These devices, which measure any change in mass, come in two varieties: quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices.

QCM sensors have a resonating disk and metal electrodes on each side. While applying the gas sample to the resonator’s surface, the polymer surface absorbs VOCs from the environment. Thus its mass increases, which increases resonance frequency. As the U.S. Navy has long used QCMs, this technology is familiar, developed, and commercially available. A QCM sensor is fabricated by screen-printing, wire bonding, and MEMS. Althoug it can measure a 1.0 Ng mass change, its MEMS fabrication and interface electronics is a major disadvantages. QCM sensors are quite linear in mass changes, their sensitivity to temperature can be adjusted, and their response to water can vary for the material used.

MEMS techniques should be handled carefully, for the surface-to-volume ratio increases drastically as dimensions approach the micrometer levels. Measurement accuracy is lost when the increasing surface-to-volume ratio begins to degrade the signal-to-noise ratio. This problem occurs in most micro-fabricated devices. SAW devices have much higher frequencies. Since 3-D MEMS processing is unnecessary, SAW devices are cheaper. As with QCM devices, many polymer coatings are available. The differential devices can be quite sensitive. However, interface electronics require more complex electronics than those of conductivity sensors for both QCM and SAW sensors. Also, as the active membrane ages, resonance frequencies can drift and so must be detected for frequency by time. SAW devices are commercially available and sensitive to mass changes at the 1.0 pg level.

Pattern Recognition

Any e-nose’s primary task is to identify an odorant and perhaps measure its concentration. After the signal processing step comes the crucial step of pattern recognition: preprocessing, feature extraction, classification, and decision-making. A database of odors must be formed for comparison purposes.

Preprocessing accounts for sensor drifts and reduces sample-to-sample variation. This can be done by normalizing sensor response ranges, manipulating sensor baselines, and compressing sensor transients.

Feature extraction involves dimensionality reduction, a crucial step for statistical data analysis, since the database’s examples usually are subject to financial constraints. The higher dimensionality caused by sensor arrays is reduced to relevant pattern-recognition information and thus extracts only significant data. As most dimensions are correlated and dependent, it is better to reduce dimensionality to a few informative axes.

Feature extraction usually is accomplished by classical principal component analysis (PGA) or linear discriminant analysis (LDA). PCA is a linear transformation that finds the maximum variance projections and the most widely used technique for feature extraction. But as PCA ignores class labels, it is not an optimal technique for odor recognition.

LDA seeks to maximize the distance between class label examples and minimize the within distance, and thus is a more appropriate approach. LDA is also a linear transformation. For instance, LDA might better discriminate subtle but crucial odor projections, whereas PCA can remove the high variance random noise in a projection.(4)

The classification stage identifies odors. Classical classification techniques are KNN (k nearest neighbors), Bayesian classifiers, and ANN (artificial neural networks]. KNN with, say, 5 nearest points will find the 5 closest matches from the precompiled database. The closest match will be assigned as the tested material’s odorant class.

Bayesian classifiers first assign a posterior probability to the classes in the lower dimension and then pick the class that maximizes the predetermined probability distribution. ANN is closer to biological odor recognition. After being trained by the odor database, it is exposed to the unknown odorant in order to recognize the largest applicable response odorant class. The classifier estimates the class and places a confidence level on it.

In decision-making, risks and application-specific knowledge are considered in order to modify the classification. All decisions are reported-even a nonmatch.

Conclusion

As this article indicates, we can expect great progress in this area. And with each step forward, science and technology will continue to point toward the Greatest Artist’s most subtle designs and allow us to appreciate them better.

Footnotes

1. There are over 100 million receptor proteins of about 1,000 different types.
2. A human olfactory bulb contains approximately 2,000 glomeruli.
3. The terms “electronic nose” and “e-nose” are incorrect, for these devices cannot be considered “real” noses. The correct terminology should be “electronic arrays for chemical sensory and identification.” However, “e-nose” has gained wide acceptance in the literature since it first appeared during a 1991 NATO workshop in Reykjavik, Iceland.
4. Such nonlinear transformations as Sammon nonlinear maps and Kohonen self organizing maps also are used in feature extraction. These preserve the distance between pairs of examples when reducing dimensionality to 2 or 3.

References

• Baltes, Henry, Dirk Lange, and Andreas Koll. “The Electronic Nose in Lilliput.” IEEE Spectrum (Sept. 1998): 35-38.
• Barinaga, Marcia. “Salmon Follow Watery Odor Home.” Science 286 (22 Oct. 1999): 705-6.
• http://csmt.jpl.nasa.gov/enose.html.
• http://faculty.washington.edu/chudler/nosek.html.
• Malakoff, David. “Following the Scent of Avian Olfaction.” Science 286 (22 Oct. 1999): 704-5.
• Mamberts, Peter. “Seven-Transmembrane Proteins as Odorant and Chemosensory Receptors.” Science 286 (22 Oct. 1999): 707-10.
• Perkins, Sid. “Eau, Brother! Electronic Noses Provide a New Sense of the Future.” Science News 157 (19 Feb. 2000): 125-27.
• Schiffmann, Susan, and H. Troy Nagle. “The How and Why of Electronic Noses.” IEEE Spectrum (Sept. 1998): 22-32.
• Stern, Peter and Jean Marx. “Making Sense of Scents.” Science 286 (22 Oct. 1999): 703.
• Wolfgang, Gopel, and Tilo Weiss. “Design for Smelling.” IEEE Spectrum (Sept. 1998): 32-34.
• www.planetee.com/planetee/servlet/DisplayDocument?ArticleID=6899.
• www.sfn.org/briefings/smell.html.

Since the mid-1980s, there has been increasing interest in developing so-called “electronic noses” (e-noses), that is, electronic instruments that can detect and recognize simple and complex odors.1 And since the mid-1990s, nearly 20 years after the concept was originally published, the commercialization of e-noses has started to take place. The main reasons for this delay were the complex nature of the problem and the need for advanced technologies. However, the recent development of microsensor technology has led to low-cost integrated chemical sensors and application-specific microprocessing devices. This, coupled with our greater understanding of artificial intelligence, has allowed us to construct electronic instruments that perform in a manner similar to our own olfactory system.

E-noses are now being developed as systems for the automated detection and classification of odors, vapors, and gases. They are generally composed of a chemical sensing system (e.g., sensor array or spectrometer) and a pattern recognition system, such as an artificial neural network (ANN). At Pacific Northwest National Laboratory (PNNL), e-noses use ANN technology for the automated identification of volatile chemicals used in environmental and medical applications.2

The electronic nose works as follows. While a chemical vapor or odor is blown over a sensor array, sensor signals are digitized and fed into a computer. The ANN (implemented in software) then identifies the chemical. The benefits of e-noses include compactness, portability, real-time analysis, and automation.

FOOD INDUSTRY APPLICATIONS

Currently, the largest market for e-noses is the food industry. In some instances, e-noses can augment or replace panels of human experts and can reduce the amount of analytical chemistry performed in food production, especially when only qualitative results will do.

An electronic smelling device is a valuable tool for analyzing whether a product has gone bad. Potential applications of e-noses in the food industry are numerous: inspecting and grading food quality by odor; inspecting fish and beverage containers; controlling fermentation, automated flavoring, and microwave cooking; monitoring the ripening of cheese; verifying if orange juice is natural and/or fresh; testing plastic wrap for containing the odor of onions; and classifying grains and blueberry ripeness.

Using human odor panels to evaluate and control the quality of raw materials or finished products is extremely labor intensive, time consuming, expensive, and error prone. E-noses can quickly identify a characteristic odor classified as “good” or “bad” by the odor panel, thereby decreasing the workload, improving throughput, and reducing the cost of screening many samples at different stages of the manufacturing process. The system is applied easily to the manufacture and quality control of perfumes, cosmetics, and fine chemicals, as well as to packaging, monitoring environmental quality, the automotive industry, medical and diagnostic matters, and microbial classification.

ENVIRONMENTAL MONITORING

The PNNL is exploring the technologies required to perform cost-effective environmental restoration and waste management. This effort includes developing portable, inexpensive systems that can identify contaminants in the field in real time. Environmental applications of e-noses include identifying toxic wastes and household odors; analyzing fuel mixtures; detecting oil leaks; monitoring air quality, factory emissions, and hazardous chemicals; and testing ground water for odors.

MEDICAL APPLICATIONS

Since the sense of smell is important for physicians, an e-nose can be used as a diagnostic tool to examine bodily odors (e.g., breath, wounds, bodily fluids, etc.) and identify possible problems. Odors in the breath can indicate gastrointestinal, sinus, and liver problems, as well as infections and diabetes. Infected wounds and tissues emit distinctive odors, and odors coming from such bodily fluids as blood and urine can indicate liver and bladder problems. Currently, an e-nose for examining wound-related infections is being tested at South Manchester University Hospital.

In similar applications, ANNs have been used to track glucose levels in diabetics, determine ion levels in bodily fluids, and detect such pathological conditions as tuberculosis.

While the inclusion of visual, aural, and tactile senses into telepresent systems is widespread, the sense of smell has been largely ignored. PNNL recently proposed a more futuristic application of e-noses for telesurgery. In this application, an e-nose would identify odors in a remote surgical environment. These identified odors then would be transmitted electronically to another site, where an odor generation system would recreate them.

The next decade should see the cost of e-noses fall dramatically, with the result that they will be used not only in industry but also in everyday life. They can be used, for example, to detect tainted foods in the refrigerator, ensure clean clothes in the washing machine, detect poor air quality in the car, and perhaps even help us monitor our own health.

FOOTNOTES

1. J. W. Gardner and P. N. Bartlett, Electronic Noses (Oxford, UK: Oxford University Press, 1999).
2. http://www.ivanhoe.com/docs/backissues/electronicnose.html.