We perceive the world around us through colors, sounds, geometric patterns, and smells. Although various theories and models have been proposed to explain how the senses are processed in the brain as sight, sound, and smell, we are still in the infancy stage of understanding these magnificent senses that God has gifted to animals and humans.

There are two types of photoreceptors in our eyes, which are in the form of rods and cones. These receptors are equipped with the ability to perceive certain wavelengths of vibrations in the outside world as light and color. They are sensitive to colors and to differences between black and white. The hundreds of color tones perceived by the cone cells reveal themselves by combinations of different wavelengths of red, green, and blue light.

Hearing receptors located in the inner ear are stimulated according to the frequency and volume of sounds, similar to the logic of vibrating strings of different lengths in an instrument and are perceived as sound in the brain. In the olfactory sense, there are about 400 different receptors.

Before the sense of smell occurs in the brain, an extremely complex decoding system operates within millions of odor molecules. It is not yet known how the signals from these receptor cells are brought together to trigger a particular sense of smell. If the codes of smell can be decoded, it may be possible to understand how animals find mates, offspring and food, and how molecular regulation is involved in understanding emotions, stress, appetite, and mood.

One of the biggest problems in understanding odor is that there is not always a relationship between the chemical structure of a molecule and the smell that is sensed. Two chemicals with very similar structures can smell very different, or two very different chemical structures can be perceived as almost the same odor. Often, fragrances are not a single substance, but a mixture of tens or hundreds of aromatic (odor-producing) molecules. For example, the smell of coffee or fermented cheese consists of a mixture of dozens of different proteins, fats, vitamins, and carbohydrates.

In this complex structure, the question is how a certain molecule gets in contact with other molecules to produce a common odor pattern. When you look at the tastes of three or four different types of pears or apples, the smell is different, as is the flavor of each one. When we isolate each of the minerals, organic and inorganic compounds in the structure of the apple, the smell they will produce individually is very different from the smell they will produce together. The fact that each of the apple types exhibits a different smell is related to the amounts and combinations of substances it has, but we do not know much about how this happens.

It is more or less understood how the two types of receptor cells in the human eye respond to light and the chemical processes involved in their operation. But it’s unclear how signals from 400 different kinds of olfactory receptors come together to trigger a particular sense of smell. Also, because working with the proteins in the membranes of these receptors is a difficult task, what these membrane proteins look like and how they work is based on guesswork. However, thanks to the developments in the field of computers and artificial intelligence in data analysis, we can hope that there will be more progress soon in decoding odors and the fine architecture of biological structures.

In a study published in Nature, thousands of scents were introduced to a panel of people and to an AI system. “Using the structure of these molecules alone, the AI algorithm did well at predicting the smell of compounds compared with the average group assessments …, and it performed better than the typical individual sniffer.” One thing that can be deduced here could be that smelling is a subjective experience. Artificial intelligence, on the other hand, is man-made and does not have a soul, and is also deprived of the experiences that people encounter throughout their lives. Thus, it has been successful in dividing odors into groups more accurately in the predictions it makes by looking only at the codes of the molecular structures uploaded to the computer [1].

An arcane password

There are millions of olfactory neurons in the nose. They are created as the biological hardware used for sensing smells, and each typically carries only one type of olfactory receptor. The group of genes encoding them was discovered in the early 1990s, a discovery that was awarded with the Nobel Prize [2]. Each of these receptor types can recognize one or more odors, and each odor can also be recognized by multiple receptors. Therefore, it has been calculated that millions of neurons connected to 400 different types of olfactory receptors will respond to approximately one trillion chemical odor substances with the combination they will make together. Aashish Manglik, a biochemist at the University of California, San Francisco, argues that this system is incredibly perfect and flexible, and that this is the only way to understand the incredibly diverse chemistry of nature.

An important step in decoding odors will be to understand what these olfactory receptors look like and how they recognize chemicals. However, according to Manglik, these proteins, which are located in the membranes of the recipient cell, are very difficult to decipher, because it has not yet been possible to produce and isolate enough proteins to be analyzed.

Some of the scientists who study the subject of smell on insects have figured out the structure of the receptors that insects use to smell [3]. However, although the olfactory receptors in insects appear to be completely different from those in mammals, it is estimated that the working logic is the same [4].

Recently, two more receptor cells in the olfactory system of mice were deconstructed, and it was found that both of these receptor types detect clearly bad odors, such as the smell of fish or rot, which are the main components of common body odors in many animals [5, 6].

One research team succeeded in imaging for the first time in an electron microscope how a protein in a human odor receptor binds to an odorant molecule. It was seen how propionate, the cause of a pungent cheese smell, enters and binds to a pocket on the receptor, then changes the shape of the receptor and transmits information. Still, the exact nature of this occurrence is not understood [7].

Although the researchers are very excited, they are also aware that solving just one of the hundreds of receptors that detect odor substances will not yet say much.

They later saw that two separate compounds, both of which smelled of menthol, bound to the receptor at different places. They think that different odors probably bind to a single receptor in different places, triggering different events. This helps explain the level of complexity in scent codes. It can explain why two different chemicals can have similar odors, or why chemically similar compounds can smell so different. For example, the two types of carvone compound have the same structure as the mirror image of each other, but while one of them is perceived as the smell of mint, the other smells as cumin or dill. The mystery of this is hidden in these olfactory receptors. Efforts to unravel this mystery continue; our findings so far can be compared to a few drops of water from the ocean of God’s infinite knowledge. Meanwhile, with the help of techniques such as machine learning and artificial intelligence, odor molecules that bind to 20% of the olfactory receptors in humans have been identified. During the studies, they scanned millions of compounds to figure out which molecules would bind to the two receptors and found that one of these receptors was tuned to the smell of orange blossom and the other to the smell of honey [8].

Nose-brain connection

When a molecule of an odor attaches to the receptor cell and is processed, the resulting molecular information goes to a brain region called the olfactory bulb, which is located behind the bridge of the nose, and from there to the olfactory cortex in the brain. This olfactory cortex is much more mysterious. Research focuses on understanding how the information from the receptors is organized in the brain and by what principles and patterns the perception of smell emerges. If the mystery of this is solved, it may be possible to generate a similar pattern in the brain to detect a certain smell as if there is a substance even though there is no smell.

It seems that many new paths of discovery will be opened in the future of our world. Perhaps we will be able to understand how animals react to certain odors and find their direction. We may develop new techniques for eliminating harmful insects, diagnose diseases such as tuberculosis, cancer, and diabetes through smell, and discover how the coronavirus destroys smell receptors and suppresses the sense of smell. We might also produce devices that detect explosives and drugs, as well as electronic noses capable of identifying substances in contaminated wastewater. It is even possible that smartphones will one day be enhanced to detect and transmit smells, just as they currently process images and recognize voices. In relation to these developments, aromatherapy is another potential field that could advance significantly if we can identify which areas of the brain are activated by specific scents and how this knowledge can be applied to treat diseases.

Some faith traditions attribute the unpleasant odors associated with certain psychological disorders to metaphysical beings, such as demons. As we deepen our understanding of the olfactory system, we may uncover some of the underlying causes of these psychological conditions. The wisdom behind practices like drawing water into the nose during ablution in certain forms of worship may also become clearer, as scientific research continues to reveal more about the connection between the nose and the brain.

References

1. Smith, K. (2024): The most mysterious sense: Cracking the odour code. Nature, Volume 633, 5 September.
2. Buck, L. & Axel, R. (1991): A novel multigene family may encode odorant receptors: A molecular basis for odor recognition. Cell 65, 175–187.
3. Butterwick, J. A. et al. (2018): Cryo-EM structure of the insect olfactory receptor Orco. Nature 560, 447–452.
4. del Mármol, J., Yedlin, M. A. & Ruta, V. (2021): The structural basis of odorant recognition in insect olfactory receptors. Nature 597, 126–131.
5. Guo, L. et al. (2023): Structural basis of amine odorant perception by a mammal olfactory receptor. Nature 618, 193–200.
6. Gusach, A., et al. (2023): Molecular recognition of an aversive odorant by the murine trace amine-associated receptor TAAR7f. Preprint at bioRxiv https://doi.org/10.1101/2023.07.07.547762
7. Billesbølle, C. B., et al. (2023): Structural basis of odorant recognition by a human odorant receptor. Nature 615, 742–749.
8. Jabeen, A., de March, C. A., Matsunami, H., & Ranganathan, S. (2021): Machine learning assisted approach for finding novel high activity agonists of human ectopic olfactory receptors. Int. J. Mol. Sci. 22, 11546.

Every one of our five senses is unique in their own way. The miraculous sense of smell is pointed to in the famous story of Prophet Joseph when his father Prophet Jacob said, “I sense the fragrance of Joseph” from afar, and when he rubbed his shirt to his sightless eyes, he regained his sight (Qur’an 12: 94, 96). This suggests that smell, or sweat, may be a guide for researchers regarding the diagnosis and treatment of diseases.

Some of the novel characteristics of the sense of smell have recently been explored. Studies jointly conducted in three emerging disciplines, namely artificial intelligence (AI), nanotechnology, and molecular chemistry, have suggested that it may be possible to diagnose one’s diseases using the smells of his or her sweat, urine, and breath.

Imagine that Parkinson’s disease, multiple sclerosis, kidney failure, Crohn’s disease, pulmonary hypertension, chronic kidney disease, or any type of cancer could be diagnosed through a simple assessment of the smell of your breath without any painful procedure including having to insert a probe, syringe, or any other apparatus into the body. It would be so convenient, wouldn’t it? We know that breathalyzers are being used for many decades to detect drunk driving by analyzing the sample breath from a driver. Scientists have been curious as to why such an approach could not be utilized to detect other diseases in this manner and have thus engaged in an interesting research.

A team of researchers from universities in Israel, France, Latvia, China, and the United States have recently managed to diagnose 17 diseases with an accuracy rate of 86 percent using an analyzer that determines the molecules in breath samples with the help of AI software.

The scents that emanate from human bodies are as unique as fingerprints in that they are determined by genetics and metabolic differences among human beings. Human babies know their mothers from their scents, and they would not accept being nursed by a woman other than their mother unless they are extremely hungry. Every household has its unique smell. Couples know each other from the scents of their loved ones. The wise purposes for why such an abundance of smells exist in our lives include their whetting our appetite for eating food, feeling spiritual gratifications, and knowing and avoiding spoiled food and other potentially harmful substances. Evidently, when human health deteriorates, foul byproducts – such as the defective molecules that are the result of fermentation, death, decaying, or wrong synthesis due to faults in cells, tissues, or organs – start to move around the body through blood circulation. Some of these consequential defects are removed from the body via perspiration through the skin, urination through the kidneys, or exhalation through the lungs.

Molecular composition of breath

To better grasp this process, we need to have a closer look into the molecular composition of breath. When we exhale, we release nitrogen, oxygen, carbon dioxide, argon, and water vapor. Human breath also contains organic volatile chemical molecules in gas form that can readily blend into air due to having a high vapor pressure at a normal temperature. US biochemist Linus Pauling, one of the founders of modern quantum chemistry and molecular biology who won the Nobel prize in chemistry in 1954 and the Nobel peace prize, examined volatile substances in 250 samples of human breath using gas-liquid chromatography in 1971. Pauling is commonly regarded as a pioneer in the field of modern breath analysis. According to a study conducted 40 years later, exhaled breath contains more than 3,500 chemical compositions mostly consisting of trace amounts of volatile molecules [1].

Most of these compositions are metabolic products synthesized or decomposed based upon the functioning of the organism as a whole and some of them are called biomarkers. For instance, lung biomarkers are related to the processes that occur in the respiratory system, especially in one’s airways. Assessments of these biomarkers is useful in the diagnosis of inflammatory diseases of the respiratory system. Some examples of these biomarkers include hydrogen peroxide and isoprostans, nitric oxide derivatives, metabolites, inflammatory markers such as arachidonic acid (for instance, prostanoids, leukotrienes and epoxides), and adenosines. Breath temperature is also considered to be an important factor in prototypes of an “electronic nose” which takes all of these factors into consideration and in which new analytical and computer technologies integrate them together to produce unique results have started to be manufactured. In regards to diagnosing diseases through odor detection by animals, it is known that dogs are capable of diagnosing Mycobacterium tuberculosis, which causes tuberculosis, by smelling breath while rats can do it by smelling the sputum [2].

In a study, a blood sample taken from a patient with colon cancer was tested against blood samples from healthy subjects and a dog was able to diagnose the sample from the patient with cancer at every run. This study demonstrated that there is such a thing like the scent of a specific cancer and chemical compounds that are unique to cancers may be circulating in our body.

A research team led by professor Hossam Haick from the Israel Institute of Technology collected breath samples from 1,404 healthy people (control) and people suffering from 17 different diseases. These diseases included lung cancer, colorectal cancer, head and neck cancer, ovarian cancer, bladder cancer, prostate cancer, kidney cancer, gastric cancer, Crohn’s disease, ulcerative colitis, irritable bowel syndrome, idiopathic Parkinson’s disease, atypical Parkinson’s disease, multiple sclerosis, pulmonary hypertension, preeclampsia toxemia, and chronic kidney disease.

The wet mucosa layer covering the insides of our nose typically attracts volatile chemical molecules. When odorant molecules come into contact with receptor cells located inside this mucosa epithelium, they become bound to these receptors and send electric signals to some 2,000 glomeruli, which are spherical structures consisting of nerves that can receive smells and encode them as electric signals in the olfactory bulb in the front and base of the brain. There are approximately 2,000 glomeruli around the surface of the center of the sense of smell. Smelling consists of interpretation of the patterns encoded based on the odorant molecules in these glomeruli. The human nose is capable of detecting one trillion smells. In Haick’s study, nanotechnology and machine learning replace the biological brain in the process of smelling.

Haick-led scientists used an organic carbon detection layer that controls the electrical resistance of layers made up of nanotubes through which nanotechnological molecules pass through in order to identify volatile organic compounds associated with specific diseases. The electrical resistance varies based on the type of volatile organic chemical molecules. AI software analyzes these changes in a machine learning system to determine which molecule occurs differently in ill people than healthy people in any specific disease. So far, gastric cancer was detected with an accuracy rate of 92-94 percent in the measurements made on more than 8,000 patients in clinics. Thus, researchers were able to discover that every disease has its own unique breath print [3].

As the diagnosis of diseases with the help of smell makes progress, the number of cases in which odor patterns in breath or sweat are determined increases. This raises the hope for detecting many diseases at an early stage even before their symptoms are manifest. An accuracy rate of 90 percent has been achieved in early diagnosis of preeclampsia, a disease associated with high blood pressure during pregnancy [4].

Dr. Hirsch says that the device that can diagnose lung cancer with an accuracy rate of 90 percent is able to detect a special “odor” coming from cancerous cells. The oily sebum secreted from the skin before any symptom of Parkinson’s disease has a musk-like scent which is not bad, but different from the normal. When physicians use the same technology to detect Parkinson’s disease, other cancers, kidney failure, multiple sclerosis, and Crohn’s disease, the accuracy rate is 86 percent. Ammonia in one’s breath is a sign of kidney failure. Researchers from the University of Illinois have developed a single-use device that can detect the breath print of kidney failure at a very early stage. There are even cases where doctors can diagnose certain diseases just utilizing their nose sensitivity without the need for special equipment. For instance, when a person’s liver starts to deteriorate and fails to decompose certain toxins these pollutants will accumulate in one’s urine, sweat, and even breath, and the odor of raw fish will be sensed.

If you have an infection in your gingiva, bacteria will secrete waste products that smells like rotten eggs due to hydrogen sulfide. This odor tells us that the person in question has gingivitis, a dental abscess, or poor oral hygiene. Diabetic patients have a fruit-like breath odor. This may indicate diabetic ketoacidosis as the body uses fats for energy due to a lack of sufficient insulin or lack of proper use of existing insulin. Sour breath is one of the early symptoms of infectious mononucleosis, caused by Epstein-Barr virus. In some rare metabolic diseases such as trimethylaminuria, foods such as fish, liver, eggs, and some vegetables cannot be digested in the intestines, and as they decay, they give off a strong “fishy” odor. In maple-syrup-urine disease, caused by a genetic disorder, infants are unable to decompose certain portions of proteins, and as a result, their urine, earwax, and other body liquids smells like maple syrup.

References

1. Popov, A. T. (2011): Human exhaled breath analysis. Annals of Allergy, Asthma & Immunology, Volume 106, Issue 6, p. 457.
2. Bijland, L.R., M K Bomers, M.K., Smulders, Y.M. (2013): Smelling the diagnosis: a review on the use of scent in diagnosing disease. Neth. J. Med.Jul-Aug. 71 (6): 300-307.
3. Nakhleh, M.K., Haick, H. et al. (2017): Diagnosis and Classification of 17 Diseases from 1404 Subjects via Pattern Analysis of Exhaled Molecules. ACS Nano 2017, 11, 1, 112–125.
4. Nakhleh, M.K., Baram, S., Zaher, R.J. et al. (2016): Artificially Intelligent Nanoarray for the Detection of Preeclampsia under Real-World Clinical Conditions. Advanced Materials Technologies 1 (9): 1600132

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 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.

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.

Based on a sensible interpretation of the cosmos and events, we considered the arrival and departure of each existence in this world very normal, a process taking place in a gentle manner; this mysterious journey instilled in us profound spiritual expansion, for it was a means of reunion, each action and replacement was like being discharged of duty and freedom from the burdens of service at the end of which await the realms of divine favors hat is constantly heard, touched and smelt; we, as humans, don’t hear or feel certain things after a certain period of time. In medical terms, this process is called “adaptation to the senses.” If we have to go into a very stinky place, we intensely feel the smell at first, but after a while, we begin to feel it less. Another example can be given about those who wear glasses. They sometimes search for their glasses in different places thinking that they have lost them, even though they still wear them.

Our friend’s adaptation levelwas a little higher than the normal, but considering the disturbance of those who wear glasses would feel on their noses, it is better understood that this adaptation is a great favor of All-Powerful and All-Knowing God.

In the absence of adaptation

If we weren’t endowed with the capacity of adaptation, our brain would be busy with unnecessary information and we would be disturbed by the constant touching in our body. The cells that feel the senses are called “receptors.” There is an amazing adaptation in most parts of the cells that sense the touching in the skin. For instance, when we wear something, we feel the first touch of the garment to our body, but this feeling caused by the garment disappears afterwards. If we were to feel everything touching our skin, life would be very difficult for us. Likewise, in some patients, the adaptation to senses disappears and this makes the things harder for them. Some patients, on the other hand, develops hypersensitivity. They feel pain and suffering even by the slight touching of their garments. It is very hard to cure this illness which is called “neuropathic pain” in medicine. They feel cancer-like severe pain. Scientists are still working on the studies to stop this kind of pain.

How does adaptation occur?

Adaptation happens as a result of a different mechanism for each sense. Touching causes a liquid movement in the cytoplasm of the receptor cells. This movement is sensed by the cell and conveyed to the brain in the form of electric signals. Despite the continuation of touching, the cytoplasm movement in receptor cells is stopped after a while and no signal is sent to the brain. So, no touching is felt. But when touching stops, as a result of a liquid movement in the cytoplasm of the receptor cells, a new signal prompts the brain that “touching is over.” In short, only the beginning and the end of touching is communicated to the brain. Despite the continuation of touching between the beginning and the end, the brain (rather the “soul”) is not bothered by this redundant information. Even though, many types of receptors serve in the process of adaptation to touching, only six of them have been thoroughly studied and named. The adaptation is not the same in all receptors; fast and advanced in some of them, while in some of them it is slow and weak. For example in touching receptors of the skin (Merkel disks), the adaptation is relatively little and there is no adaptation at all in some senses such as feeling the pain. In some receptors (such as Ruffini’s corpuscles) located in dermis (bottom layer of the skin), deep organs and joint capsules, the adaptation is very little. These receptors send the weight and pressure signals required for the absence of adaptation. Weight and pressure receptors located in the joint capsule are responsible for sensing the angle degree of the joint. The brain receives information from them about the angle degree of the joints and it constantly uses it while sending orders of movement to the muscles of the skeleton. We can walk and do the other movements that require balance thanks to these perfect processes happening beyond our consciousness. If the brain didn’t know the information regarding the angle degree of the joints, some jobs that require delicate balance such as the job of construction workers wouldn’t be properly done.

Adaptation in various senses

Adaptation in seeing (accommodation): Adaptation in seeing is different from the one for touching. If we keep looking at an object, we keep seeing it. In this sense, there is no interruption in adaptation and seeing. This is another favor of God among many of His favors. If the adaptation in seeing were to be similar to the one in touching, we wouldn’t be able to do many activities that require walking, reading, sitting, standing and being in balance. All-Merciful God placed different adaptations in our eyes appropriate for the jobs that they do.

Adaptation in seeing near and far: We keep seeing an object no matter how nearer or farther we move it. Despite the change in the distance of the object, our vision doesn’t change. These processes are automatically carried out depending on the distance we look and they are operated under the framework of optical principles such as changing the shape of the eye lens and approaching of the lens to the retina or moving away from it.

Adaptation in seeing in the light and dark: Our eyes detect and adapt to the new surroundings, be it light or dark. During this adaptation process, seeing in the dark and light is made possible by adjusting the degree of vision and increasing and decreasing it one million times. The activities of the photoreceptors (in the shape of rod and cone) are carried out by an amazing knowledge and power.

Adaptation in smelling (olfaction): The smelling receptors of the nose adapt to the bad smell at a rate of 50 % in its first encounter. So, the dense bad smell felt in the first encounter disappears immediately. A minute after this encounter, the sensing of the bad smell is eliminated upon the orders coming from the brain to the nerves of smell. Garbage men or cleaners or the people working in slaughterhouse or sewerage do not get disturbed, as a favor of God, by the bad smell as much as other people do.

Adaptation in tasting: the adaptation happens one minute (at most) after the “tasting.” Yet All-Powerful and All-Knowing God created the adaptation capacity for the bitter materials very low, because most of these materials are a kind of poison for our body. Therefore when the babies unconsciously want to eat something poisonous, they take them out at once and are avoid of being poisoned.

Adaptation in temperature: The temperature receptors are intensely stimulated in sudden temperature changes. The adaptation occurs in 30 seconds or one minute as the intense of stimulation decrease. However there is no 100% adaptation, because the receptors sense both the sudden changes and constant situations. Remember, both extreme hot and cold are harmful for the body. The fact that the adaptation in this sense is limited is another favor of God.

Adaptation in hearing: When we enter a noisy environment, we are disturbed by the extreme noise. But two tiny muscles located in the middle ear contract as a manifestation of His mercy and prevent the sounds from being conveyed to the middle ear by masking all the sounds except for the ones of normal conversation. Workers in a noisy environment keep working as though they do not hear the noise at all.

Adaptation in feeling the pain: There is no adaptation in feeling the pain which is an indication of God’s mercy. If there were any adaptation to the pain, we would lose the patients before diagnosing and curing the illnesses. If a patient bothered by the gastrointestinal bleeding or appendicitis were to have an adaptation to the pain, after a few minutes he would not feel any pain before taken to the hospital and think that his illness is over and does not feel any need for a treatment. But possible inflammation of the appendix might result in the risk of death after a while.

Many of us are not aware of this perfect mechanism of adaptation. All these examples put forward the fact that the mechanisms bestowed upon our senses are very harmonious and adaptive to the working principles of our intellectual and spiritual faculties in the evaluation of various situations that we encounter in our life and they also show that humans were created as a whole. If we were deprived of such a blessing, we wouldn’t be aware of many changes that threaten our life and be bothered by the disturbing environmental conditions.

Omer Arifagaoglu is a professor of medicine. He lives in 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

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• 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.

Sight: When we look around, we see several shades of colors and hundreds of thousands of images. Human beings, and several animals, are able to see images when light enters the eye and releases an electrical signal through our the nerves to the brain. These signals are then transformed into the images, or pictures, that we see. All creatures see these images differently; some see images in different outlines in shape, color, clarity, circumstances, and distance.

Dogs, because of their hunting needs, see twice as much as do human beings. In addition, dogs have an outstanding ability to follow movement and to perceive direction, speed, and trajectory. Trajectory is what gives dogs the innate ability to plot an angle and predict an angle of movement. For example, dogs have an astonishing ability to know the exact spot where a moving object will land and know from which angle it will be coming. This is the reason why dogs are such good ball and Frisbee catchers; because they visually know the exact point of impact of an object as it falls back to the ground. Cats, on the other hand, have a different reason for being such good jumpers. Cats’ faces are flat between the eyes, a rare feature in the animal world, which makes it easier for them to work together. As a result, a cat can focus sharply and three-dimensionally, an ability that allows it to visually judge distances with great accuracy before jumping.

Rabbits, for example, are one of the few animals that can see all around them (front and back) without turning in either direction. Their eyes are located on the sides of their head, which enables them to see in all directions. Rabbits, frequent preys for predators, are always on the alert, and their eyes are located in the best place to help them see their enemies.

Human beings and wildlife animals have two kinds of vision cells that are located inside the back of the eye: cones and rods. Cones detect colors in bright light, including black, white, and gray. Rods provide sharp vision in dim light, but do not detect colors. Night creatures have more rods than cones, which provide them with sharper vision at night-but with only shades of gray. Also, to assist these creatures in the dark, they have a special layer in the back of their eyes, called the tapetum, which acts as a mirror when light passes through it. If the rod does not detect the light during the first passing, the tapetum reflects the light back to the rod, thus giving the rod a second chance to pick up on the light and see an image. It is this layer that makes some animal’s eyes shine in dim light.

An owl’s eye, for example, is so sensitive in picking up light, that research shows that an owl can follow a trial lit up by a candle 1,000 feet away (3,600 meters).1

Another amazing sight feature is found in predator birds: “telescopic” eyes that allow them to see by making a far away distant object appear larger. Birds such as the hawk and eagle have the sharpest sight of any animal. These birds have about 1.04 million vision cells in the back of their eyes, which that enables them to see a mouse from as far as one mile away.2 (Human beings have only about 130 million vision cells.)3

Although animals are believed to see colors similar to the way humans do, scientists are not sure how bees and insects see color. Scientists believe that, among some other creatures, bees, birds, and insects can see a color that human beings can not: ultraviolet colors. In addition to red, blue, and yellow, flowers often have ultraviolet patterns that show these birds and insects the way to the plant’s nectar and pollen. Such sight makes it possible for these creatures to find and feed on the flowers’ nectar and pollen.

However, not all animals have only two eyes. Jumping spiders, for instance, have eight eyes. There are two big eyes in the front, and six smaller eyes on the top of the head slightly toward the sides. The two front eyes are very well developed and act as a pair of binoculars that give the spider a clear image of objects up to one foot (30 cms) away. The little eyes are called secondary eyes. These eyes can spot moving objects and have a built-in reflecting layer that helps the spider to see objects in dim light. The secondary eyes are the eyes that actually measure the distance the spider needs to jump to catch its prey.

Hearing: Just as with other senses, human beings and animals have different levels of hearing. Most animals have only two ears, which helps all of us locate the origin of a sound. Having two ears helps us locate where a sound comes from. Since sound reaches the ears at slightly different times, this makes a sound louder than in one ear. This difference in volume and arrival time in one ear is an indication as to the origin of the sound. Sound is expressed in hertz (cycles per second), which are repetitive vibrations per second. Adult human beings, with a normal hearing ability, can hear from twenty to twenty thousand cycles per second. Amazingly, wolves can hear up to eighty thousand cycles per second, and dogs can hear up to thirty-five thousand cycles per second, almost twice as many as humans.

Cats have a surprising hearing of between fifty to one hundred thousand cycles per second-three to five times than what human beings can hear. In addition, a cat’s ear has thirty muscles that control the ear muscles that can rotate 180 degrees. This give cats the opportunity to hear its surroundings without moving its head.

An owl’s ear, however, are located at different heights. The difference in height enables an owlit to determine if a noise is coming from a high distance or from the ground. Another interesting feature of many owls is a flat heart-shaped face. The shape of its face functions as a reflector that makes faint sounds louder. These two features enable owls to be the great hunters they are and helps them to hunt in the dark.

Not all animals and insects have “ears”; some have holes in either in their head or in another part of their body, and others have eardrums, such as birds, insects, and fish. Fish’s ears, for example, are located under its skin behind its eyes. This way, a fish can pick up on vibrations that pass their skin under the water. Other fish makes some of these noises by vibrating an internal organ or by rubbing their fins together. Fish use these vibrations to communicate with other fish, to mate, to warn other fish, or to swim together in groups.

Smell: Animals with different smelling needs have been created with different noses and different smelling abilities. Among the different abilities and noses, an elephant’s nose stands out in many individuals’ minds; at least mine. These animals’ noses are so amazingly equipped with different functions, it is surprising. An elephant’s nose (trunk) and upper lip weighs, on average, 300 lbs. (136 kgs.), and can take up and hold more than one gallon (3.7 lt.) of water at a time for spraying on another animal’s back. The trunk is also strong enough to pick up large logs, yet functional enough to gather thin blades to eat. In addition, an elephant can raise its trunk high in the air to smell if any predators are in the area. Another function that I grin at, is that elephants weighing so heavy sink to the bottom of a rivers when they try crossing it; however, they use their noses as snorkels when crossing a deep river by lifting their noses high above the water line to breathe.

Dogs have an astounding sense of smell; they are one of the animals with the best sense of smell. Dogs can pick up odors in concentrations of one part per trillion. A book called Scent, published by veterinarian Dr. Hugo Verbruggen, and dog trainer Milo D. Pearsall, mentions an experiment that illustrates how well dogs can pick up odors. It mentions that if a single gram of butyric acid, a chemical constituent in human perspiration, were released in a ten-story building and evaporated, a human being might be able to smell the odor for a very short moment by sniffing at a window. A dog, in comparison though, would be able to pick up the odor in the same amount if it were to spread over a city the size of Philadelphia anywhere within the city up to an altitude of three hundred feet (90 meters).4 It also mentions that if humans had only ten percent of a dog’s smelling ability that dogs have, we would have a totally different understanding of our world we.

Camels are desert animals that have been created with special channels that can hold moisture in the dry desert. Also, when the wind blows, a camel can close its nostrils to keep out the sand and dust.

Ants also fascinate me. These tiny creatures use odors to identify if an ant belongs in their colony or if it is an intruder. In addition, when an ant dies a certain odor is released, and other ants in the colony will carry the dead ant to a burial site. An experiment has been performed by scientists that placed this “dead” odor on a healthy ant. Although the marked ant was struggling and kept returning to the nest, other ants constantly carried this marked ant to their burial grounds in the belief that it was dead.5

Taste: Taste and smell are chemical senses. Although scientists can only guess what an animal can and does taste, they do know that animals have different taste buds. Taste buds are made up of tiny taste cells that enable us to taste sweet, sour, bitter, and salty substances. Mammals have the most taste buds, while birds have the fewest; insects have none. However, these animals and insects have special taste cells to detect the certain foods they need for survival.

Touch: All animals have a sense of touch. Many scientists believe that touch is the most important sense. The sense of touch indicates if we are hurt, cold, hot, and much more. Blind and visually impaired individuals rely on the feeling of touch to read Braille. Many animals and insects, however, have built-in antennas that help them avoid too close physical contact with other insects and help them detect food and surrounding conditions.

A blowfly (any fly that deposits its eggs on meat or wounds), for instance, uses its antennas to determine if the wind conditions are best for flying. If the wind is blowing too fast, the blowfly will wait until the wind calms down. This is an important feature, for this insect would not be able to survive flying in a strong wind.

Many animals and insects rely on the sensing of vibrations. For example, a spider relies on the shaking of its web to understand if it has caught food or if another spider has come to mate. A spider feels the vibrations through its long legs by waiting at the edge of its web. It is understood that when a spider returns to its web, it shakes the web to see how it vibrates. The results will let it know if something has been caught.

It is also interesting that some animals seek and show affection through touch, just like human beings do. Cats, dogs, monkeys, seals, and lions are some examples that show love and affection. As a cat owner, it is interesting to see the understanding of affection through touch. They enjoy being petted and seek for affection. A question asked by people, who have a cat or have been near a cat, is that why do cats purr and what causes this noise. Scientists believe that purring is produced by blood in a large vein in the chest that vibrates and is then magnified by air in the windpipe.6 Someone petting a cat can actually feel this vibration. Cats usually purr when they are happy or when being shown affection. However, the cat’s purr is more than a sign of content. Kittens, unlike many animals, are born blind and deaf. The vibration of their mother’s purring is a physical sign that the kittens can feel; it is somewhat of a signal to the kittens to be close to the mother and nurse. Also, the kittens’ purr is a signal back to the mother that their kittens are getting their milk and are healthy. This is an extraordinary survival mechanism.

“Super-natural senses”: There are several sensing abilities that scientists can not explain or categorize due to the several unique senses possessed by several animals and insects. Among them is the mosquito’s remarkable sense of heat that leads them to their victims. Female mosquitoes follow have several, however, the most remarkable one is that they can sense temperature differences of less than 1/250th of a degree Fahrenheit. This amazing sense of temperature enables them to land on the warmest and best vein of blood for food.

Another sense scientists have difficulty explaining is that birds, bees, and some other creatures have magnetism. Just as a compass has a magnetic needle that points north, these creatures have natural magnets that help them migrate and find food by using the earth’s magnetic field. They have natural tiny crystals of iron oxide, or also called magnetite, made front iron found in their blood. This enables these adorable creations to still find their way even when they can not see the sun.

People for many years have been puzzled how animals can sense an earthquake before its any “obvious” signs. One of the explanations is that animals, as described throughout the article, have unique and even, in some cases, better senses than human beings. Therefore, they are able to pick up on vibrations, sounds, and odors that humans physically can not, which may indicate to them that a disaster is about to occur.

A final note: Besides their senses, animals have a uniqueness and wondrous superiority over other animals the other with their physical attributes and characteristics. For example, some animals see or hear better than other animals, and some animals have unique physical attributes that other animals do not have. If you look at the beautiful and majestic kingdom of animals, you will find that each animal has a different beauty and awe that deserves much appreciation. This is a component that makes this world a fascinating and perfectly created one.

REFERENCES

1. The National Wildlife Federation “What do Do Animals See, Hear, Smell, and Feel?” (1990).
2. Ibid
3. Ibid
4. Roger A Caras, A Dog is Listening. Summit Books. 1992.
5. The National Wildlife Federation” What do Do Animals See, Hear, Smell, and Feel?” (1990).
6. Arline Bleecker, “Why Do Cats Sulk?” Globe Digests. 1998.