Canine sense of smell


Last week, as we commenced the new topic of nose ailments, and having dealt with general considerations relative to the canine nose, it was promised that this week we would spend some time on the canine sense of smell.

You may recall that I have often said that the dog is not really an ‘eye’ animal, meaning that its functional sight would probably be the least important of a dog’s senses. Instead your canine ward greatly relies on hearing and smelling to function optimally.

When you watch your dog ‘Rex’ (NB: Dogs should really only be given one-syllable names like Max, Pat and so on, instead of Maximillian von Flaschendorf und Hohenheim; he really only responds to the first syllable – Max) run around your yard or an open space sniffing here, smelling there, he is actually carrying out an important orientation function. A veterinary colleague, Dr Randy Kidd, had this to say about his observation of his dog’s sense of smell in action:

20130210steve“I watch as he trots ahead, nose just above the grasses, head ever on the swivel, left to right and up and down – air-sniffing, selecting scents, veering to wherever the pleasures of his nose take him. Suddenly he stops, moving into a clump of grass, snorts, burrows his nose deeper into some fragrance I will never know, an odour that recalls some aromatic memory, perhaps a primitive recollection from even before he was born. He digs into that memory of odour. Digs with his paws for a while, snorts, then decides it is a lingering smell no longer worthy of his work. He rises up, glances my way … and then lifts his leg and marks this location for any who might follow.”

The canine sense of smell and repertoire of scents is much larger and more acute and expansive than a human’s. The dog collects scents by ‘air-smelling’ (sniffing volatile oils that are travelling in the air) and sniffing the ground. A dog’s nose is ideally made for sniffing, and allows for expansion on the inhalation of air, and contraction to prevent the entry of unwanted objects. When a dog sniffs, he inhales the scented chemicals into his nasal cavities, where they are trapped in mucus and processed by the millions of specific sensory cells. Expiration forces air out the side of the nostrils so that its exit doesn’t interfere with odours still in the air or on the ground.

Several thin, delicate hairs in the nostrils extend from each of the sensory cells into the nasal cavity, and each of these hairs (‘Cilia’ is the scientific name) contains many scent receptors. The cell receptors trap the smells, and deliver the messages back, through specifically designed apparatuses, to nerve centres in the brain.

Actually, other brain centres which deal with memory, emotions, pleasure, etc, are interconnected. Consequently, a single simple inhalation may result in a whole set of meanings, memories and emotional ties that only your dog can know and interpret.

Much of the deeper work of trying to understand the sense of smell has been done on humans, and not so much research on dogs. How can a research scientist ask a dog what he feels or remembers when he smells a certain odour?

But we do know that dogs have much more surface area within their nasal cavities (as compared with humans), and this area is well supplied with sensory cells – estimates of the total number of these cells vary and depend on the dog breed, but they have been cited as more than 125 million. (This compares with estimates of human numbers that are in the 5- to 10-million-cell range.)

In addition, the dog has devoted a tremendous amount of his brain tissue to ‘smelling’ cells. (Some estimates allocate one-third of the dog’s brain to the chore of scenting). All this adds up to a canine smelling ability that is thousands to millions of times greater than that of his human counterpart.

We also know that we can use the dog’s incredible sense of smell to benefit mankind in ways we are only beginning to imagine. Today’s working scent dogs are involved in search and rescue (some dogs can follow a trail that is more than a week old), finding cadavers (dogs have even detected drowned people in a depth of 80+ feet of water), detecting explosives, firearms, and drugs, and even scenting tumours in human patients. Early work has begun to use dogs to test the breath of humans – to help diagnose internal diseases before they become evident with other methods. Wow!

We’ll continue with this theme next week.

Have a pleasant week!

Please implement disease preventative measures (vaccinations, routine dewormings, monthly anti-Heartworm medication, etc) and adopt-a-pet from the GSPCA’s Animal Clinic and Shelter at Robb Street and Orange Walk, if you have the wherewithal to care well for the animals. Do not stray your unwanted pets, take them to the GSPCA’s Clinic and Shelter instead. We still have the free spay and neutering programme. Exploit it. If you see anyone being cruel to an animal, or if you need any technical information, please get in touch with the Clinic and Shelter by calling 226-4237.

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