**3. Signals between organisms**

Music is often produced by an individual or group of individuals, and listened to, or perceived by, another individual or group of individuals. There is an excellent example of such action in cell signalling and that is the generation and response to pheromones (Agosta, 1992; Kell *et al*., 1995). Here small compounds are made and released into the medium outside of the organism (Figure 1). They are then carried in the flow of the liquid or gas, perhaps the atmosphere, which surrounds the organism to be sensed and responded to by another individual of the same species, but not the individual organism that released them. Pheromones are used for attracting a mate and sexual arousal for example. In human behaviour interestingly often music is used for the same purpose.
