Olfaction (also known as olfactics) refers to the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates. For air-breathing animals, the olfactory system detects volatile or, in the case of the accessory olfactory system, fluid-phase chemicals. For water-dwelling organisms, e.g., fishes or crustaceans, the chemicals are present in the surrounding aqueous medium. Olfaction, along with taste, is a form of chemoreception. The chemicals themselves which activate the olfactory system, generally at very low concentrations, are called odors. History As described by the Roman philosopher Lucretius (1st Century BCE), different odors are attributed to different shapes and sizes of odor molecules that stimulate the olfactory organ. The modern counterpart to that theory was the cloning of olfactory receptor pr

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