2. Sense of Smell

IMG_6949Up next in the Sense Series is olfaction. Many of us know that dogs are expert sniffers, but it’s hard to imagine just how great they are at it without directly experiencing it for ourselves. My favorite attempt to demonstrate just how dramatic this difference is was done by Stanley Coren in his book “Do Dogs Dream?” He explains that we can smell one five-millionth of a gram of butyric acid (a component of sweat) evaporated into a cubic meter of air. While this sounds fairly impressive, dogs can detect this same amount of butyric acid dissolved into 250,000 gallons of water. For another comparison, we can just barely smell 1 gram evaporated into a ten-story building. Dogs can smell this 1 gram dispersed over 135 square-miles, up to a height of 300 feet in the air — roughly the size of the city of Philadelphia. The natural question following this statement is: how?

Humans are not very good sniffers. We only care to notice the really good ones or the really bad ones and our nasal anatomy is mostly to blame. We use the same nostril to inhale and exhale, which means as soon as we get ahold of a good smell, we let it out just as quickly. In order to get an adequate sniff of something we have to repeatedly inhale without exhaling. In other words, we hyperventilate. This also lends itself to habituation of the olfactory world around us. Your perfume only smells great for the first few minutes after you spray it and the rest of the day you’re left wondering if it’s still there.

Dogs would consider our noses obsolete, as they’ve evolved way beyond the simple inhalation method. They draw in a current of air, while displacing the air already inside their nose – either out through the slits of their nostrils or deeper into their noses and out of the way – in order to allow the new air access to the lining of the nose. Wind generated by the exhale creates a current of air over the new scent that helps to pull it into the nose. If you watch your dog sniff the ground, you will notice dust move about underneath his snout. This is him exhaling while sniffing, something we can’t do or we’ll lose the smell. In addition, they have a bony shelf-like structure in the nasal cavity that traps air, preventing it from being pushed out during exhalation and allowing enough molecules to accumulate for recognition.

This method of sniffing provides dogs with many superpowers. One of which being the avoidance of habituation to smells. They can constantly reset their sensory receptor cells by refreshing the scent in their noses. Therefore, a dog has a potentially endless amount of time to sniff.

Now that the smell has made it into the nose (again and again and again and..), it is welcomed by over two hundred million sensory receptor sites. For comparison, humans have about six million. Some of their sensory receptors fire together, in response to different molecules, creating an exponential difference between our abilities to receive olfactory information. In other words, a beagle’s nose may be millions of times more effective than ours.

This means that, while we can smell a pungent rose, dogs can smell the difference between each rose petal. They can not only tell that a caterpillar made an appearance on an individual petal, but also how long ago and even in which direction it left, by wiggling each nostril independently of each other.

But for dogs, sniffing doesn’t stop with the nose. They also possess a vomeronasal organ located above the roof of their mouth and below the floor of their nose. In other animals, flehmen, or lip curling, occurs in order to get pheromones to their vomeronasal organ. Dogs, however, do not curl their lips. Instead, their wet noses and sometimes straight consumption brings pheromones into the mouth or nose for access to this organ. Pheromones are found in things like feces, urine, and sweat, which can explain why dogs often get up close and personal with these seemingly inappropriate bodily products.

In addition to having the tools to gather more scents, dogs also have the hardware necessary to process these smells. The area of the brain devoted to analyzing smells is about forty times greater in dogs than in humans. These olfactory bulbs make up an eighth of the mass of a dog’s brain. That’s proportionately larger than the occipital lobes, or visual processing center, of our brains.

The takeaway of this information is that dogs were designed to smell. It explains many of their odd behaviors, like crotch-sniffing, jumping up to our faces, licking our mouths, nuzzling our armpits, rolling in decaying matter, eating feces, and sticking their heads out of moving cars. They’re constantly trying to “see” the world around them. If we deprive our dogs of sniffing a house guest, we’re basically asking them to meet someone blindfolded. If we constantly pull their leash while we’re out on a walk, we’re not allowing them to read the newspaper, to get all the daily gossip about the neighborhood. But, worse than that, we’re not allowing them to satisfy an entire eighth of their brain.

Next time you’re mad at your dog for wanting to stay at that fire hydrant for way too long, think about everything that’s happening in his nose. Who’s the walk really for? If it’s for your dog, call it a smell walk, and let him take his time seeing his world.

This blog will address canine olfaction, and how our best friends’ abilities have been used to our advantage, more in the future.
Until then, what else can we do to stimulate their oversized snouts? What strange behaviors do we now have a better understanding of?


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