[The power of odors--pathogenic or unpleasant].
Modern toxicological studies have prompted us to rethink the role of olfaction and odours in our world. Our sense of smell is able to discriminate between an almost unlimited number of compounds of different chemical composition at extremely low threshold levels. Olfaction is classified as a chemical sense because of the bimolecular excitation process between the stimulant and receptor molecule. Receptor molecules of the olfactory epithelium have a variable region of the molecule which can differentiate between an unlimited number of aromatics. The sense of smell--the oldest phylogenetic sense--is therefore in very intensive contact with the "chemical" environment. Virtually all of the aromatic products which we are exposed to are highly complex chemical mixtures of numerous individual components which have a toxic potential little investigated to date. The perception of odours can be interpreted as a warning--a protective mechanism necessary for survival. At the same time, however, the exaggerated use of perfumes is held to be indicative of a highly cultured status. Unlike any other sense, that of smell is directly connected to archaic areas of the paleocortex region of the cerebral hemisphere, so that an odour will fill us with joy or abhorrence outside of our control. Odours cannot, therefore, be analyzed rationally without eliciting instinctive reactions, positive or negative, which result in acceptance or rejection. The highly developed memory for odour types is believed to be coupled to the route of the olfactory tract. The use of olfactometry today enables odours to be reliably quantified and characterized in a reproducible manner.