FIVE FACTS ABOUT SMELL @ALICEBARTLETT

1. Humans have three chemical senses • Smell • Taste • Trigeminal

2. 1.2% of people do not have a sense of smell* • In 1987 1.5 million people were tested with six different compounds, and 1.2% of them reported not being able to smell anything. This condition is known as anosmia.

*I am one of those people Hi.

3. Some smells are smellier than others and nobody knows why • Test by isolating the smelly compound and diluting it in water. • Dilute until people can no longer identify the compound present.

***SUB-LIST TIME*** TOP FIVE SMELLY SMELLS: 1. Grapefruit juice 2. Cork odour 3. Butter 4. Pepperoni 5. Strawberry

Comparison of detection thresholds in water: • Citral [Lemony]: 32ppb • Menthene-8-thiol [Grapefruity]: 0.00001ppb ! Menthene-8-thiol (grapefruity) is 3.2 million times smellier than citral (lemony).

4. There are seven primary smells These classifications are more psychological than chemical but are very handy for talking about smells.

***SUB-LIST TIME*** SEVEN PRIMARY ODOURS: 1. Camphoraceous (moth balls) 2. Floral 3. Pepperminty 4. Ethereal (detergent) 5. Pungent (vinegar) 6. Putrid (bad eggs) 7. Musky

5. We don’t really know how humans detect smell. If you are ambitious to find a new science, measure a smell. -Alexander Graham Bell 1914

You have between five and six million smell receptors

You have 347 different types of smell receptor. ! One smell receptor will detect several (similar) molecules and react with different intensities to them.

Your olfactory receptors seem to act in a combinatorial way.

THE PROBLEM • The thing we don’t know is: what causes an olfactory receptor to trigger. There are two competing theories and neither have been disproven.

“Shape Theory” states that molecules fit into receptors like a lock and key. • Shape theory makes sense intuitively and has historically been the preferred theory

BUT THERE ARE PROBLEMS • Some compounds with vastly different shapes smell the same. • And some compounds with very similar shapes smell totally different.

Let’s talk about limonene • Limonene has two mirror molecules. The left molecule smells like Lemons and the right molecule smells like Turpentine.

“Vibration Theory” states that it is not the shape but the vibration pattern of the molecule that determines its odour. • This would allow molecules of the same shape to smell different • BUT there are examples of molecules with the same vibrational energy that smell different!

These two theories are the best we have and it’s been 100 years. **SLOW CLAP**

THIS TALK IS OVER.