...		...

Dogs and their sense of smell is one of the greatest things that define them. When a dog makes a decision it is usually based on smell first, then sound, then sight.

This article explains exactly how miraculous a dog’s sense of smell is.

A dog’s sense of smell is its main communication tool. When a dog sniffs other dogs, they learn about their age, sex, and status. A person’s mood can also be evaluated by how they smell to a dog.

A dog can detect tobacco in “ 27 layers of polythene or locate termites” that no other instrument can detect. They can identify the faintest of smells, even when they're heavily masked by other scents - such as the odour of trace amounts of heroin that have been hidden in pungent aniseed.” (ref 1),

There has been much research about how dogs can detect illnesses in humans and in particular various forms of cancer. One of the biggest stories was a study into how they detect ovarian cancer. (ref 3)

Dogs can detect scents we don't even know exist.

HOW do dogs detect the faintest smells?

Dogs have much more nasal membrane than we do. “In humans, the area containing these odour analysers is about one square inch, or the size of a postage stamp. If you could unfold this area in a dog, on the other hand, it may be as large as 60 square inches.” (ref 4) It is not only the number and quality of olfactory receptors that provides dogs with amazing scent capabilities, but it is thought that different areas of receptors can tune into different smells and some smells that humans cannot even differentiate.

In general it is believed that the bigger the dog and the longer his muzzle, the keener their sense of smell.

To give an indication of how important a dog’s sense of smell is, it is believed that some dogs have even evolved to have longer ears to help channel scent molecules into their nose. (ref 6) Meanwhile daschunds were breed to have shorter legs so that their highly tuned nose could be closer to the ground when running at full speed, thus keeping on track better.

A dog's brain is also specialized for identifying scents. The percentage of the dog's brain that is devoted to analyzing smells is actually 40 times larger than that of a human! (ref 4)

The table below (ref 4) indicates the typical number of Scent-Detecting Cells in People and Dog Breeds. A comparison of raw numbers between humans and dogs does not indicate its scent detection ability, because the sniffing techniques a dog uses, the size of the brain processing areas etc act as a multiplying factor on a dogs scent abilities. That is why it's been estimated that dogs can identify smells somewhere between 1,000 to 10,000 times better than humans can.

The DOG SMELL MECHANISM

Almost every part of the dog is optimized to enhance their smell capabilities. Their nostril shape is designed to “allow expiration out of the sides of the nose so that fewer scent molecules in the air or on the ground are disturbed.” (ref 6)

Inside the nose of both dogs and humans are bony scroll-shaped plates, called turbinates, over which air passes. A microscopic view of this organ reveals a thick, spongy membrane that contains most of the scent-detecting cells, as well as the nerves that transport information to the brain. (ref 4)

“It's believed that this sheen of moisture acts almost like Velcro, trapping scent molecules as they waft by. Along with the sticky mucus in the nasal passages, this allows dogs to collect and store large numbers of passing molecules.” Ref 1

Scents don't just drift conveniently into their noses. A dog's nostrils act like little antennas. Dogs wiggle them to collect scents and figure out where they're coming from (directional information). When a dog raises its head and sniffs they are interrupting their breathing pattern to gather some new information. If a dog does not sniff, scents are not being drawn near their olfactory sensors and they are effectively turning their sense of smell off (and giving their brain a rest from processing the information).

“Sniffing is accomplished through a series of rapid, short inhalations and exhalations. A bony subethmoidal shelf, which is found below the ethmo-turbinate bones of the nasal cavity, forces inhaled air into the olfactory epithelium. Washing out of the region upon exhalation does not occur due to the nasal pocket created by the bony subethmoidal shelf. The nasal pocket permits the odor molecules that are unrecognizable in a single sniff to accumulate and interact with olfactory receptors.” Ref 5

The scent molecules gleaned with each sniff are ultimately distilled and transported to various parts of the brain, much of which is devoted to remembering and interpreting them. Dogs have the ability to tap into this scent storage bank throughout their lives. Ref 1

"Odors have a powerful influence on both the behavior and the physiology of the dog, smell memories last for life and affect almost all canine behavior." Scents tell them where they are, who a dog or person is, and even what state of mind that other creature happens to be in. ref 1

HOW DOGS DECODE SMELLS

“Dogs can layer smells in their mind very much the same way that we layer things visually. So if I have a quilt and it’s got a bright pattern and I throw on top of it a book and throw on top of the book my glasses and throw on top of the glasses a pen, well I can see the book, the pen, the glasses and the quilt all at separate layers. If a dog walks in and you’re cooking spaghetti, then in fact the dog will smell the meat, will smell the green pepper, will smell the onions and they will layer it in exactly the same way that we layer things visually.” Ref 2

Besides dogs having many more olfactory sensors in their nose and a much larger part of the brain dedicated to understanding these smells, they have an additional olfactory chamber called the vomeronasal organ that also contains olfactory epithelium. “The vomeronasal organ, known as Jacobson's organ, consists of a pair of elongated, fluid-filled sacs that open into either the mouth or the nose. It is located above the roof of the mouth and behind the upper incisors. (ref 5)

“Dogs access the organ by licking or snapping the air, drawing chemicals into the mouth. All mammals have a VNO, but it was thought to be inactive in humans since prehistoric times.” Ref 6

As the olfactory receptors in the nasal cavity are anatomically distinct from those in the vomeronasal organ it is believed that they may be able to sense different smells.

HOW DOGS communicate with other animals

Dogs mark territory to let other dogs know that they have visited. Their urine contains scent signals, as do the anal glands, stools, and saliva. Smelling a dogs behind or its waste lets a dog know how old a dog is, which sex, neutered or intact, relative or stranger.

A dog smelling these scents and comparing them to its scent memory will then catalog the new scent into memory. Even in familiar places with familiar people, dogs will regularly sample scents to detect if there have been any changes or to re-familiarize themselves with an area.

WHY dogs roll in ‘bad’ smells

Dog roll in pungent smells such as dead fish and birds not only because the fragrance is enjoyable, but mainly because they can use the “scent of another creature to disguise themselves from something they're preying on and to get closer to it. Dogs don't have to think about prey and predators very much anymore, but the urge lives on” (ref 1)

Why dogs sniff their owner

Just like dogs store a ”scent memory” of other dogs and animals they use it to remember humans, and whether these humans were good or bad to them the last time. A dog will trust its sense of smell over vision (how a person looks) or sound anytime. Sniffing their owner will also tell them if they are sick or where they have been.

Dogs can use the smell of their owner as a comfort while the owner is away (assuming that you are a good owner) by curling up with an article of clothing such as your socks. Also while dogs are excellent readers of body language, “a your dog can tell a lot about your mood just by your smell. A person's body odor will change with their mood and dogs can understand what state their owners are in.

Dogs have good vision and hearing however “perfume, deodorant, cigarette smoke, and other odors that linger on skin and clothing all combine to make up a person's individual smell. Changing that composite smell "picture" can change how a dog interacts with a person, while it readjusts it’s scent memory.

Breed specific hunting

Just as different dogs were originally bred for different task such as working dogs or sporting dogs, many breeds developed scent capabilities for specific hunting purposes. Basset Hounds, Beagles and Dachshunds follow scents of rabbits, while Coonhounds track raccoons and Pointers and Spaniels air-scent birds. ref 6

CONCLUSION

A dog’s scent organs, brain processing, and adaption to hunting specific prey is one of the most miraculous forms of evolutionary selection ever witnessed in the animal world. An animal’s ability to detect and decode scents is a product of its breed as well as their health, nasal structure, mental capacity, nutrition and conditioning.

While you may consider your pet to be a house dog, one of the most satisfying things that it can do is roam free and detect and analyse scents in an off lead park. The amount of skill and brain processing power that this takes is astounding and beyond the reach of any man made machine.

The next time you wonder why your dog wants a walk, or see how much they enjoy themselves off lead, whether they are tracking dogs, rabbits or birds, consider all of the incredible components that have gone into providing them one of the most keen smell senses in the animal kingdom.

Article by Bruce Dwyer. If you wish to use any of this information please refer to the article as a reference and provide a link to http://www.dogwalkersmelbourne.com.au

References

Ref 1   http://kryptiks-lair.tripod.com/id12.html

Ref 2   http://www.abc.net.au/rn/science/ss/stories/s1330617.htm

Ref 3  http://www.sciencedaily.com/releases/2008/06/080626090901.htm

Ref  4  http://www.dummies.com/how-to/content/understanding-a-dogs-sense-of-smell.html

Ref 5  http://www.aces.edu/pubs/docs/U/UNP-0066/

Ref 6  http://purinaproclub.com/sportingdog/SportingLibrary/tracking-a-dogs-keen-sense-of-smell.aspx