Pheromones are frequently employed in courtship routines. These chemicals are released in tiny quantities into the surrounding medium and they have a powerful physiological effect on members of the opposite sex. They are common in moths and account for the brush like antennae of the males which makes them more sensitive to the chemicals as they drift from the receptive females into the air. Humans also release pheromones and they are known to cause dramatic changes in the heartbeat rate, blood pressure and dilation of the pupils; they clearly stimulate adrenalin release, or the autonomic nervous system. We are unaware of their presence or their effects upon us.