Last week I was reading “Surely, You’re Joking, Mr. Feynman!“, a wonderful autobiography of the curious and hilarious Nobel winning physicist Richard Feynman. I was struck by one of his curiosity kicks: he wanted to see how well the human nose could smell. Were our smelling powers stunted in comparison to those of other animals? Could we take a book off the bookshelf and be able to tell if someone has read it simply by smelling it? Could we tell if someone has merely held it in their hands? He found the answer to be YES! I however, was not so sure. Feynman, after all, was quite the joker. I wanted to try it out for myself. But first, we had to learn a bit about the nose and how it works.
The nose is quite an interesting sense organ. When learning about the five senses, we often talk about how our sense of smell is so closely tied to our sense of taste. Remarkably, smell is responsible for 80% of the taste we associate with different foods! Our nose aids us in survival, it alerts us us to when food has spoiled and become potentially dangerous. It also alerts us when there is a fire or a leak of toxic chemicals that we may need to get away from. Our sense of smell is incredibly useful in our daily life.
As we breathe in, tiny airborne molecules lifted from the things in our environment enter our nose. As they become trapped in our mucus, they come in contact with special cells in our nasal cavity called olfactory neurons. These neurons are unique in that they are the only exposed nerve cells in the entire body! Cilia (tiny hairlike structures that line the surface of cells) pull the molecules to the neurons, stimulating them. Each molecule lines up to specific receptors, fitting them like puzzle blocks in a play toy. When the molecules bump into these neurons, they fire off an electrical impulse that runs through receptors in the olfactory bulb above your nasal cavity.
There are more than 1,000 different types of receptors which can identify up to 10,000 smells and varying intensities! Our olfactory receptors number in the millions and span an area the size of a postage stamp (for comparison, the olfactory sensors of dogs could cover the area of 60 postage stamps!). Once these receptors are triggered, impulses are sent to your brain, identifying the smell and triggering the proper response. Interestingly, these responses can range from a sense of urgency (fire danger), fond recollection (a familiar smell from childhood), pleasant feelings, or, of course, hunger.
Once we had an understanding of how the nose works, it was time to play with our sense of smell and see what it could do! We wanted to explore its role in aiding our survival. Would Kat and I be able to tell the difference between edible and inedible items based on smell alone?
BLIND SMELL TEST
Variety of edible items (apples, yogurt, crackers, etc)
Variety of inedible items (pine-sol, shoe, book, etc)
Small containers to hold your items
1. Have your partner stay in another room (or another area – no peeking!) while you fill your containers with your test items. We used a lemon, an apple, yogurt, an orange, pine-sol, a shoe, kettle corn, soap, vanilla, soap, and an onion. Make sure to mix them up so there is not a predictable order of smells.
2. On your paper, number and label the test items. Make a chart labeled Item/Edible/Inedible/Identified.
3. Blindfold your partner and slowly guide him/her to the table. See if your partner is able to identify any smells along the way.
4. Sit your partner down and begin testing! One by one, raise each dish under your partner’s nose. Ask whether it’s edible or inedible, as well as whether they can identify what the smell is.
5. Switch places!
We found that we were able to identify the edible/inedible nature of the items with 100% accuracy. Unexpectedly, we both confused the lemon and the onion when it came to identifying the smells!
As we age, our ability to identify subtle differences between smells decreases. Test this by sampling a larger age pool in your experiment.
FOLLOW YOUR NOSE!
Insects also have olfactory neurons and use them to identify scents, often in the form of chemical pheromones (scents that are used for communication). These olfactory receptors are located in their antennae, which they use to sense their environment. We’re going to demonstrate how ant scouts lay a trail of pheromones to lead others to a food source!
A strongly scented oil, perfume, or air freshener spray
Tile floor, or make a big paper trail out of construction paper
Go into a different room and load your sponge with a strong smelling scent.
While your partner is in another room, wipe the sponge along the floor, making a trail of scent. We used our tile floor, but you could also make a paper trail with construction paper and wipe the scent along that. Or, you could take it outside and spray along a concrete surface. When the trail is finished, place an apple or another tasty treat at the end of the trail.
Bring your partner in the room and secure the blindfold on him/her.
Pretend to be ants! Close your eyes and crawl along on the floor, with your partner leading the way. See if your partner can follow the trail all the way to the tasty treat!
Trade places! Have your partner lay a trail for you to follow.
Ant scouts lay a chemical trail as they hunt for food, allowing other ants to find the food once it’s discovered. As the other ants traverse the trail, they lay their own pheromones down on top of the scout’s, strengthening the scent. What would happen if you placed an obstacle over the scent trail?
Lay a pillow or other relatively large item over your trail and see if your partner can still follow it. Turn a fan on near your trail and see if that decreases your ability to sense the molecules as they enter your nose. What if you place a cotton ball with another scent on it over the trail? Will your partner still be able to follow it?
Take your experiment outside! Place a stick over the middle of an ant trail (don’t crush any ants!). Does it effect their ability to follow the trail? What would happen if you took a cotton ball with scented perfume and marked a line over the trail?
NOTE: After you make your observations, make sure you remove any obstacles so you don’t impede the ants’ food finding mission! Leave nature as you found it.
Finally, we were ready to try the experiments that had set us off on this course of aromatic curiosity! Richard Feynman was able to tell whether a book had been handled or opened simply by smelling it. Would we be able to do the same?
YOU CAN’T SMELL A BOOK BY ITS COVER…
1. Books on a bookshelf (or piled in a stack)
2. A partner
With your partner in another room, choose a selection of 5 books (make sure they are all right next to each other!).
Take one book off the shelf and rub your hands all over it. Make sure you only touch one book. When you’re finished, put the book back in its place on the bookshelf.
Call your partner in the room and point to the selection of books. One by one, have your partner pull each book off the bookshelf and smell it. Can your partner tell which book you’ve handled?
Trade places! Will you be able to tell which book your partner has touched?
Will this work on any surface? Try DVD cases, tools, silverware, the wall – anything!
SOMEONE HAS BEEN READING MY BOOKS!
There is a distinct smell that books have. The paper, the ink, the binding, the glue, all of these things culminate into a very specific “book smell”. Can you tell if the seal of a closed book has been opened?
The set up here is the same as in the previous book smelling experiment. However, instead of rubbing your hands all over the book, all you are going to do is open it, rifle through the pages once or twice, and put it back. Will your partner be able to tell which book you opened and will you be able to do the same?
Kat and I found the answers to these questions to be a resounding YES! We could tell with surprising accuracy whether books had been touched or opened simply by smelling them! We could smell the scent of the person who had touched the book, and we could smell a difference in the dust on and inside of a book if it had been opened. We were both very excited to be able to use our nose as detectives to gather clues in our library!
We found that this excitement carried over into many other areas of our daily life. Once we began paying close attention to the smells around us, we found our ability to detect them to be dramatically heightened. We could smell the trees as we walked through the park, could detect perfumes and smells from people in crowded areas, and could even smell the remnant popcorn molecules from a fair that left two days ago! We took our newfound delight in scent with us to the grocery store, to our garden, and to nearby bakeries.
The sense of smell is a wonderfully fun thing to play with. But, don’t take our word for it, try it yourself! Just stay away from the garbage can.