Olfaction exhibits both high sensitivity for odours and high discrimination between them. We suggest that to make fine discriminations between complex odorant mixtures containing varying ratios of odorants without the necessity for highly specialized peripheral receptors, the olfactory systems makes use of feature detection using broadly tuned receptor cells organized in a convergent neurone pathway. As a test of this hypothesis we have constructed an electronic nose using semiconductor transducers and incorporating design features suggested by our proposal. We report here that this device can reproducibly discriminate between a wide variety of odours, and its properties show that discrimination in an olfactory system could be achieved without the use of highly specific receptors.

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Membranes prepared from the olfactory mucosa of the rat show a high level of adenylate cyclase activity. The activity increases up to 2-fold in the presence of physiologically relevant concentrations of odorants and is inhibited by Ca2+. The level of cyclase activity found is sufficient to explain the speed of olfactory transduction, which occurs on a time scale of tens of milliseconds.

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The reaction between NaN, and I, in aqueous solution with liberation of N, is induced by both Na,S,O, and Na,S,O,, and studies of both processes have been made over fairly wide ranges of conditions. The induction by Na,S,O, which yields H,SO, and N, is slow, and kinetic measurements have been made by determining the rates of consumption of iodine and of production of N,. The effect of [I-] on both rates is characterized by a pronounced minimum in the region of [I-] = 0*01-0'02. The results are accounted for in terms of a chain mechanism, involving the intermediates S,O,Iand S,O,N; (or S,O;), with different primary steps in the regions of low [I-] and high [I-]. The latter correspond t o the first steps in reactions which have been found t o take place in absence of N;, viz. the reaction between S, O; -and I, in presence of very low [I-] and the reaction between S,O;-and I-. The former of these has been studied kinetically but as yet no mechanism is proposed for it. The products of reaction in S205---I,-N~ systems include S,O;-, H2S04 and N,. The reactions are too fast to follow by ordinary kinetic methods and experimental work has been limited t o investigation of the over-all stoichiometry and of the relation between I, consumed to Na,S,O, consumed under a variety of conditions. A possible chain mechanism for the reaction is suggested. Based on this work an experimental method was evolved by means of which the rate of the direct reaction between Na,S,O, and I, could be measured in mixtures containing excess I,, and a reaction mechanism derived from these data is proposed for the I,-S,O;reaction. The mechanism suggested is