In nature the siting of the organs responsible for picking up odours is very variable. In vertebrate animals such as man, the forward part of the head, usually just above the mouth is the invariable site. In the invertebrates this is far from the case. In the insects, odours are sensed by the antennae or feelers which project forward from the head. In the various worms the sensory cells are sited in pits on the side of the head and in flies they are even found on the feet. In each case, however, nature has contrived to locate these sensory organs in the most appropriate place where they can provide the maximum of information. Basically, in man the receptor area for smell is an off‐shoot of the respiratory system. (Fig. 1) A smell, odour, aroma — call it what you will — consists essentially of particles of gas and vapour and, as such, one cannot be aware of its presence until some of it enters the nasal cavity either via the nose, or, alternatively, by the back of the mouth.