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This week: the sense of smell
Christmas allows me a short respite from my hectic schedule to relax at home and have a quiet day.
Some of my readers may already know that I am  the proud owner of four beloved dogs. There is a terrier cross, but we don't know what the mix is, a Pomeranian, an Afghan hound and a shih-tzu.  None of these breeds is famous for its sense of smell as all are  toy breeds except the Afghan hound, which is a sight hound that traditionally hunts with excellent vision rather  than smell.
I live in a village house in Sai Kung, and I am lucky enough to have an outdoor roof space. I am not the only one  who takes advantage of the open space on the roof.  My cats and dogs love to sunbake, especially during the colder months.
On Christmas Day, all my dogs were sunbathing  upstairs while I was a couple of floors down, sneakily opening a bag of chips. After munching on the chips for about two minutes,  there was a loud clamouring of lots of little feet rushing down the stairs like a  mini-stampede.
It would seem I wasn't nearly stealthy enough, and four drooling dogs suddenly surrounded me with desperate looks in their eyes. For my disturbing their sunbaking with an aromatic bag of chips, there was a price to be paid.
Afterwards, it got me to thinking how amazing their sense of smell is. There was no way they could have heard the bag being opened from that distance, so they were alerted only by smell.
In a related piece of  news,  on  Christmas Eve, a pet dog in  Britain, while on a walk, unerringly sniffed out a stash of amphetamines hidden in a grove. Apparently it was a major seizure, with the concealed drugs worth more than GBP500,000 (HK$7.73 million). What was amazing about this was, the dog wasn't  trained for drug detection.
It would surprise many to know that our canine friends, even short-snouted ones  such as  shih-tzus, can sense odours at concentrations nearly 100 million times lower than humans are able to.
Dogs in the wild rely on their sense of smell for hunting; their developed olfactory senses allow them to decode the smells of friends and foes alike. It is especially important for animals that live in habitats where their food is well-camouflaged and hard to see. A dog's sense of smell is directional and stereoscopic, like our sense of sight, and allows them to home in on a smell.
So what makes a dog's sense of smell so exquisitely sensitive? During the first year of my veterinary science course, I learned that the part of the brain in dogs that deals with the olfactory sense is one of the few areas much more developed  than the same area in us lowly human beings.
Dogs have more than 220 million  olfactory receptors in their nostrils, while humans have only   5 million.
Dogs also have another secret to their sense of smell; they have an extra olfactory organ that we don't have. It is called a vomeronasal organ, and it is a sac located above the roof of the mouth just behind the incisors. It enhances a  delicate sense. The vomeronasal organ is said to detect pheromones that are excreted by other dogs and elicit certain types of sexual behaviour.
Little chemical particles in the air travel up the dog's nostrils. Moisture in the nose dissolves those particles, which allows more of the particles to come into contact with the smell-sensor nerve endings  in the nose.
Have you noticed that dogs sniff a lot? Dogs often perform multiple sniffs, which is actually a  specialised olfactory function. The sniffing action traps and concentrates particles over the smell-sensing nerves, further enhancing the dog's sense.
A dog sniffing the pavement is like  humans reading the daily newspaper; they can gather a library of information from that dry, harsh pavement.
Our doggy companions have a symbiotic relationship with human beings, as we find new uses for their sense of smell.
In the city,  sniffer dogs are used by customs officials to sniff out contraband  such as illegal drugs, concealed humans,  agricultural products and unreported currency. As members of  the police force, these valuable animals are also used to sniff out bodies in homicide cases.
Many sniffer dogs have been touted as heroes for finding survivors of the September 11 attacks  and hikers lost and injured in the wilderness.
As a clinician, I usually don't have favourites when it comes to treating sick animals. I try to do my best in each  circumstance. But any time a working dog from customs or the police force comes into the clinic, I become more alert  as these are animals that save people's lives.



Urban Jungle