Your dog and even cat rubs your nose in his superior scenting skills every day. But what exactly is it about his nose that makes it so much better than ours?
It doesn’t take an anatomist to see there are obvious external differences between the human nose and that of the dog and cat. For one thing, dogs and cats have moist noses while people have dry ones. This moist nose is a common feature of macrosmatic animals (meaning animals with an acute sense of smell). It may attract odor molecules and keep them in the vicinity of the nasal openings. But the real differences between our noses and those of our pets can’t be seen from the outside.
The internal nose is divided into two nasal cavities that run the length of the muzzle in dogs and cats. These are not simply hollow cavities, but are occupied by a scrollwork of very thin, curved bones creating an intricate labyrinth. Their surface is covered with a layer of mucus and cells called the olfactory epithelium. The mucus probably dissolves odorants and helps control their access to the olfactory receptors, the tips of which poke up through the mucus.
The larger the nasal cavity, the more complex the network of bony scrolls, which allows for a greater area of olfactory epithelium. German Shepherds, for example, have an olfactory area of 170 square centimeters, compared to the Pekingese with only 20 square centimeters. The cat has about 40 square centimeters, and the human only four square centimeters. The greater the olfactory area, the larger the number of olfactory receptors. Again, the German Shepherd has 220 million olfactory receptors, the Dachshund 125 million, the cat 60 million, and the human only six million.
When your dog inhales normally, most of the air bypasses the areas of greatest olfactory cell concentration. Only when he’s actively sniffing is the air directed over the olfactory area. When trying to detect faint odors, dogs tend to sniff more rapidly rather than more deeply.
It’s hard for us to comprehend how much better dogs or even cats can smell compared to us. The dog is the scenting champion of any animal so far tested, beating out even the most sophisticated scent detection devices on the market. For example, the dog’s ability to detect acetic acid, a component of human skin secretions, is 100,000,000 times that of humans when tested in laboratory trials.
Only a few breeds of dogs have been compared to each other under controlled laboratory conditions; of these, German Shepherds were the best, averaging 35 percent better than Fox Terriers in one study, and better than spaniels or Dobermans in another.
The Bloodhound, the recognized master trailer of the world, was not included in these studies. It’s thought that his long ears and profuse wrinkles serve to stir up ground scents and catch them around the face and nose, further aiding his tracking ability, but this has never been tested.
The signals from the olfactory receptors travel to the olfactory bulb of the brain by way of long fiber bundles in the olfactory nerve. Each bundle travels through one of several small holes in the skull (called the lamina cribosa). The olfactory bulb of the human brain is tiny — smaller than a kernel of corn — whereas that of the cat, and especially that of the dog, make up a significant part of their brains.
Dogs, cats, and humans can lose their sense of smell (the technical term for not being able to smell is to be anosmic). This can happen when a blow to the head causes the nerve bundles to be sheared off as they pass through the lamina cribosa. Fortunately, because these olfactory cells have the unique ability to replace themselves, they often grow back within two months and the sense of smell will return. Tumors, inflammation, irritation, and (in dogs) distemper, can reduce or eliminate the ability to smell. Anosmic dogs and cats get along quite well, and their owners seldom even suspect a problem. Unlike anosmic humans, they don’t seem to have reduced appetites.
We experience a different world with each of our senses than the world our pets experience, but perhaps no world is as foreign to us as their rich olfactory world, a world to which we will forever remain hyposmic (one last tech term, meaning to have a reduced sense of smell).
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About the author: Caroline Coile is the author of 34 dog books, including the top-selling Barron’s Encyclopedia of Dog Breeds. She has written for various publications and is currently a columnist for AKC Family Dog. She shares her home with three naughty Salukis and one Jack Russell Terrier.