Odour subjectivity

ODOUR THRESHOLD The minimum concentration of a substance at which the majority of test subjects can detect and identify the substance s characteristic odour. 

Odour Legislation and controls Nuisance Subjective, empirical... 

Odour Legislation and controls Subjective, empirical ASTM methods... 

The lack of connection between the two phenomena is, of course, to be expected since colour is an objective phenomenon whereas odour is subjective, or, as Euzicka puts it, colour has a physical and odour a chemical influence on the human senses. 

It seems evident therefore that the unsatisfied affinity of an odoriferous body plays a fundamental part in the production of its odour by reason of one or more chemical reactions taking place in the olfactory organ the reactions must necessarily be complicated and rapid. They are at present entirely unknown and problematical, but no very great progress in the knowledge of this subject is likely to be made until the chemical properties of the osmoceptors have been determined. 

In 1899 Thoms isolated an alcohol from Peru balsam oil, which he termed peruviol. This body was stated to have powerful antiseptic properties, but has not been further investigated until Schimmel Co. took up the subject. The oil after saponification was fractionated, and after benzyl alcohol had distilled over, a light oil with characteristic balsamic odour passed over. It boiled at 125° to 127° at 4 mm., and had a specific gravity 0 8987, optical rotation -1- 12° 22, and refractive index 1-48982. This body appeared to be identical with Hesse s nerolidol, whilst in physical and chemical properties it closely resembles peruviol. The characters of the various preparations were as follows —... 

We add to the above-mentioned hydrocarbons, which during the operation should be kept thoroughly cool, a little more than the molecular quantity of fuming nitric acid or nitro-sulphuric acid. The acid should be gradually run in and the whole then allowed to stand undisturbed for from one to two hours, the resulting mass being then poured into water in order to get rid of the excess of acid. The well-washed substances thus obtained are then subjected to distillation by means of steam, whereupon simultaneously formed bodies, which smell like nitro-benzol and overpower the musk odour, readily distil over, whilst the pure substances remain behind. ... 

Bioassay of alternate molecular forms supports the view that the ORs are capable of resolving isomeric distinctions in neutral (non-biological) odourants. Stereochemical pairs of odours were tested for differential sensitivities in the blind subterranean mole rat (Spalax ehrenbergi). The subjects responded to one enantiomer, but not to its stereoisomer. Both sexes were attracted to the odour of R-(-)-carvone but unresponsive to S-(+)-carvone in contrast, males and females were repelled by the odour of (+)-citronellol, but not by (-)-citronellol (Heth et al., 1992). The lack of responsiveness by mole rats could be central due to lack of salience, or peripheral due to hyposmia/anosmia for one isomer. Both carvones have distinct odours for the human nose. 

Both primitive and advanced forms have been examined for vomeronasal excitation. The turtle VN nerve was the subject of EOG recordings elicited by small organic molecules and by specific signal compounds (Tucker, 1963 Hatanaka, 1987). The simple arrangement of the chelonian accessory area (Fig. 2.8) allows air or liquid delivery hence the preferred odourant vehicle varies with habitat across the aquatic or terrestrial turtles, and the land tortoises (Chap. 1 and Halpem, 1992). 

When choosing odours, particularly if you are interested in identication of individuals, it is important to make sure that the stimuli are equally familiar as otherwise the subjects may respond on the basis of novelty rather than cues of individuality (Martin and Beauchamp 1982). Also, the order in which the odours are presented should be counterbalanced so that order effects do not influence the results. Results from a recent study by Brown and colleagues illustrate the typical pattern of sniffing in this task (Fig. 6.1 Lee et al. 2003). 

The principal benefits of the habituation-dishabituation test arise from the speed of testing and the minimal need for equipment. Each animal may complete a nine trial session in less then 30 minutes. An additional advantage comes with the sequential presentation of the stimuli as this methodology avoids the problems associated with the mixing of vapours from different odour stimuli if the odours are presented simultaneously. The test is particularly well suited for field work as the stimuli may be presented on a substrate that the subject normally investigates, thus elicting a more natural response than one might encounter in a lab environment. 

If a null result ensues, subsequent replication of the experiment is one way to feel more confident that the results are reliable. Alternatively, the animals may be trained in a conditioned odour preference task as described below. This would enable the investigator to further understand why the subjects did not respond in the habituation-dishabituation task. Videotaping the results should also become standard practice. As well as creating a permanent record that enables behavioural... 

The towels were impregnated with one odour 60 min before their introduction into the animals enclosure by spraying the stimulus over the entire surface of the cloths (2 ml almond, 3 ml cKl). Both scented cloths (almond, cKl) smelled equally strong to human subjects. No odour, other than that of the cloth, was detectable from the towel sprayed with distilled water (3 ml). Following odour impregnation, each cloth was sealed in a plastic bag and handled with plastic gloves worn by the experimenters. 

The results were analysed by a within-subjects analysis of variance for factors of trial (1,2,3) and odour type (almond, cKl, water). The data were normally distributed (Shapiro-Wilks tests). Planned contrasts compared each of the two odours with the control odour. Only significant results are reported. The results for each behaviour were analysed separately. Four of the trials were videotaped to enable intra-and inter-rater reliability to be assessed for the observations. There was 100% concordance for both intra- and inter-rater codings. 

The subjectively perceived qualitative variance between the two sexes odours may be attributed to different levels of sex steroid homornes. However, analytical studies did not discover any qualitative differences in male and female odours (Zeng, Leyden, Spielman and Preti 1996). Only variable levels of steroid substances, like androstenes, have been found (Gower et al. 1985). 

Heritability of the odour signature is further supported by a study which showed that subjects not acquainted with odour donors were able to match odour of parents and their offspring but not odours of the spouses (Porter et al. 1985). The latter result again excluded the possibility that correct matching was due to shared environment. 

Most recently, Havlicek, Bartos, Dvorakova and Flegr (2006) tested women s body odour repeatedly across the whole menstrual cycle and focused specifically on axillary scents. Male subjects rated the smell of the samples as least attractive during menstrual bleeding and most attractive during the follicular (i.e. fertile) period of the cycle. 

For a socially living individual it is of high relevance to be aware of the emotional state of one s conspecifics. It is a fairly well-known phenomenon that animals of different species react to odour emitted by another animal which is under stressful conditions. This led several researchers to the question of whether emotional state in humans can influence their body odour. This possibility was first tested by Chen and Haviland-Jones (2000), who asked their subjects to wear armpit pads while watching 13 min excerpts from a comedy or a fearful movie. Most of them watched both excerpts. Subsequently three and six choice tests were presented to raters who were instructed to pick the sample that smelled of people when they are happy or... 

The second study used a similar method to induce specific mood in odour donors (Ackerl, Atzmueller and Grammer 2002). In this case, subjects watched a horror movie or a neutral movie. From three presented odours, female raters were asked to choose the sample different from the other two and say which one smells like fear . The different sample was picked significantly more often, but not judged correctly as fearful odour . However, fearful odour was rated as less pleasant and more intense. 

To fill this gap we specifically focused on the effect of red meat consumption (Havlicek and Lenochova 2006). We asked 8 male odour donors to adopt for two weeks a diet containing daily portions of meat, and 9 subjects to adopt a similar diet with a non-meat alternative. For the first ten days they were given a list of meals they should eat. The list of dishes for the two groups differed only by inclusion of... 

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