From Big Medical Encyclopedia

SMELL — property of various substances to influence receptors of the olfactory analyzer, causing a specific feeling.

There are many theories of the nature 3., from which the greatest recognition was gained chemical and physical. theories. According to the chemical theory the smell is a consequence of presence in the environment of certain concentration of molecules of the smelling substances. Shotl. the scientist Moncrieff (R. W. Moncrieff, 1954) suggested that on the ends of nerve fibrils of the olfactory analyzer there are receptive holes of various form and feeling 3. arises when the molecule of the smelling substance in a form approaches a hole as a key to the lock.

According to other researchers, 3. depends on affinity of molecules of the smelling substance to a membrane of the olfactory analyzer and physical. - chemical properties of molecules, i.e. from presence at them of functional groups, from a form and the sizes of molecules etc.

The greatest distribution from chemical theories 3. the stereochemical theory of J. Amoore, on a cut 3 received. substances depends on a form of its molecules, and that is very important, how precisely the form of a molecule corresponds to a form of a hole on the surface of olfactory receptors. Thus, conformed molecules or parts of molecules of substances will have similar smells.

Based on J. Amoore's theory, it was succeeded to predict a smell of synthesizable substances in some cases. However chemical theory 3. does not reveal communication between a smell of substance, its chemical structure and reactivity, and often describes only external compliance of forms.

On physical. theories, 3. — the collision of molecules of odorous substances with molecules of oxygen and nitrogen of air which is followed by the electromagnetic radiation in an infrared spectral range influencing receptors of the olfactory analyzer. Attempts to establish connection between 3 are made. substances and frequency of its infrared radiation. Shortcoming physical. theories 3. the fact that on its basis it is difficult to explain why differently optical isomerides of substances absolutely identical on absorption spectrums smell is, and at the same time the substances differing on radiation spectrums in infrared area equally smell.

It is considered that 3., perceived by the person, it is possible to divide into the main (primary) and difficult.

J. Amoore allocated seven primary 3.: camphoric, acute, mint, flower, musky, radio, putrefactive. For each of them the sizes and forms of holes were approximately calculated. This quantity of primary smells is not final; other scientists call four, six, nine, twenty five and more primary 3. From primary 3. difficult smells are combined.

The person is capable to distinguish qualitatively to 10 thousand 3., and animals — much more. It is necessary to consider subjectivity of perception 3., since 3. the same substance it is perceived by various people differently. Sensitivity to 3. changes also depending on fiziol, conditions of the person (sometimes age), temperature and humidity of the environment and other factors. It is even more difficult to distinguish intensity 3. and to classify them by force.

There is an organoleptic scale biol, estimates of force 3., on a cut intensity is classified in points: 0 — the smell is absent, 1 — a smell scarcely noticeable, 2 — clear, 3 — moderate, 4 — strong, 5 — intolerable.

Threshold sensitivity of the person to smells is rather low and is much lower, than at other animals, napr, at dogs, fishes and insects: for trinitrobutit toluene it it is equal to 5X10 - 15 g/cm 3 air (4X10 10 molecules in 1 cm 3 air), it is approximately same for oil to - you, is higher for ethane thiol and alpha ionone (respectively 4X10 8 and 3X10 8 molecules in 1 cm 3 air). Dogs perceive 3. it is less these substances in concentration on 3 — 7 orders. Some insects are capable to perceive 3. sexual attractants in incredibly small concentration — about 30 — 50 molecules on 1 cm 3 air.

A number of substances, in addition to impact on olfactory receptors (olfaktivny substances), are capable to irritate at the same time flavoring terminations of a trifacial. At the same time flavoring feelings, merging with feeling 3., change it. Also contrast — increase in sensitivity to one 3 can be observed. after influence of another or mutual easing 3. if at a gas phase there are two or more smells. One of 3. can dominate, or their action is summed up with education qualitatively new 3. (that is especially often used in perfumery); also mutual extermination of two 3 is possible. Depending on concentration of the smelling substance 3. can qualitatively change.

Despite bias of olfactory feelings, they are important for animals and the person. By means of 3. animals find food, avoid harmful, toxicants, learn about emergence of predators. By means of odorous substances animals mark «the» territory, find individuals of an opposite sex etc.

On the basis of olfactory feelings some diseases of the person still were in the ancient time diagnosed. A number of diseases at which are observed specific 3 is known to the qualified doctor. (e.g., a smell of acetone at a diabetic coma, a putrefactive smell at abscess of a lung, a smell of sourcrout at a mephitic gangrene, etc.). 3. is the strong activator of department of digestive juices, appetite raises or oppresses. 3. various origin can cause reflex reduction of blood vessels, increase the ABP level, strengthen action of the heart etc. Many data on influence 3 are saved up. on working capacity and mood of the person. Also esthetic value 3 is big., e.g. 3. flowers, perfumery products etc.

In many industries there is a profession — the taster 3. These are first of all the perfumers distinguishing the thinnest and the most difficult 3., hundreds of components including sometimes, tasters of grades of tea, wine, coffee, tobacco etc.

In criminalistics researches on identification of the person on individual 3 are conducted. By means of 3. sexual attractants (see) successful fight against mass wreckers of agriculture is conducted.

Attempts of creation of ways of objective registration 3 become. E.g., cars of some firms are supplied with the device which is not allowing to include ignition if the driver is in an ebrietas. At the heart of ways of objective registration 3. hromatografichesky, spectral, colorimetric and other techniques can lie.

See also Anosmia , Sense of smell , Olfactory analyzer , Feeling .

Bibliography: Bronstein A. I. Taste and sense of smell, M. — L., 1956, bibliogr.; Wright P. X. Science about smells, the lane with English, M., 1966, bibliogr.; Tamar G. Fundamentals of touch physiology, the lane with English, M., 1976, bibliogr.; Physiology of touch systems, under the editorship of A.S. Batuyev, L., 1976; Physiology of touch systems, under the editorship of G. V. Gershuni, p.1, L., 1971.

And. X. Tambiyev.