Amazing sensitivity

We can detect over 10,000 different smells. However, dogs have one million smell cells per nostril, and their cells are significantly larger than those of humans: small wonder they train dogs to search for illegal drugs on people or in their luggage.

Smell is one of our senses and an important one. Our sense of smell directly affects our sense of taste (do you really enjoy a good meal if your have a bad cold?).

Smell can also release emotions such as fear, happiness, and sexual desire. Some chemicals are particularly associated with the 'awakening' of the sexual response – pheromones. A male moth can detect a female by her smell or pheromone when she is miles away.

The sense of smell is one of the body's protective mechanisms. For example, the detection of smoke or burning clearly has survival value; equally, it helps to be able to discern that food has 'gone off', has turned rancid or begun to rot – think of the smell of fish that is no longer fresh. This is caused by the chemical trimethylamine. Some unfortunate people have an inherited condition called trimethylaminuria, which means that they have a fishy odour about them (see Trinculo's description of Caliban, perhaps one of the first cases to be recorded in literature).

And some people are born with a condition known as anosmia, which means that they are unable to smell or have a limited range of things that they can smell.

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