Smell is something not peculiar to human. In animals, it has no apparent appreciations, but there is good amount of identification by the animals. Not only dogs but all animals, have good sense of identification of smell. In humans, it is highly adaptive. The sense of smell is picked up by bare nerve endings from a place called cribriform plate situated at the base of skull and at the roof of nose.
From that a cluster of nerves called the olfactory bulb reaches the uncinate gyrus, a place of recognition of smell. The cortex is the highest place, where the type of smell is recognized. Thus volleys of impulses reach this cortex from olfactory nerves. There is a peculiar phenomena for all sensory nerves.
When stimulation is continuous, the rate of firing of discharges becomes less from the nerve cells, unless renewed again with different wave length of stimulus. For example we do not realize wearing our shirt or shoes after some time unless it becomes uncomfortable. This phenomenon is called sense of adaptation. The same works with smell also as continuous stimulation of olfactory nerves, reduces the volleys of neuronal stimulation less, and becomes more adaptive. Even the bad smell of rotten food, or animals, death etc may be identified by the new comer to that place, but the residents may not realize. A fisherman does not identify the smell of dry fish, but others can identify it. Likewise, the non realization of perfumes by the person wearing the perfume becomes adaptive, while when others pass by that person they may realize the smell of the perfumes.
