It's not hard to see why our ancient ancestors recruited dogs to their domestic
As well as being extremely intelligent, dogs are blessed with senses much more
powerful than those of humans. In particular, their sense of smell is extraordinarily
Dogs are capable of sniffing everything from drugs to electricity, underground
gas pipelines to ovulating animals.
Recent studies suggest that dogs may even be capable of using their
super-sensitive snouts to detect human illnesses from epileptic fits to cancers.
How Dogs Smell
Smell is the dog’s dominant sense, so much so that a huge part of its brain is
devoted to analysing odours. Dogs have two giant olfactory bulbs attached to
the brain which decode every smell they encounter. The bulbs weigh around 60
grams, four times as much as human olfactory bulbs. Given that a canine brain
is one tenth of the size of a human one, that means the canine brain has forty
times as much of its brain devoted to smell as we do.
Little wonder then that a dog’s sense of
smell is reckoned to be 100,000 times better than a humans. In tests dogs have
been able to pick up chemical solutions that form one or two parts in a
trillion. That is the equivalent of smelling one bad apple in two billion
The source of the dog’s exceptional ability to smell is its wet snout. The
moist leathery surface of the snout acts like velcro catching even the tiniest molecules of smells,
then dissolving them so that the dog’s internal, smell receptor cells can
analyse them properly. To keep his nose wet a dog must produce a constant
supply of mucus through its nasal cavities. Scientists reckon the average dog
produces a pint of this mucus every day.
What Dogs Can Smell
Dogs really can smell fear. If a dog goes into a room where a frightened dog
has just left, he will appear anxious and agitated. This isn’t, as many would
claim, some kind of ESP type response. It’s caused by a scent, an alarm
pheromone, which is produced by the anal glands of frightened dogs.
Dogs can detect odours that are up to 40 feet underground. They have been used
to detect leaky gas pipes. They can also smell insects embedded in the ground
or in woodwork. In the United States dogs are used to sniff out termite infestations.
Dogs can also pick up the faintest whiff of other creatures.
In Guam, the US Department of Agriculture’s Wildlife
Services use specially trained Jack Russells to sniff
out brown tree snakes in the loading bays of aeroplanes.
Dogs can smell human fingerprints that are a week old.
Dogs’ noses are so sensitive that they can even smell electricity. While
conducting an experiment, a researcher found that a dog could smell which of
two compartments contained an electric current. He concluded this was because
the charge resulted in the release of tiny amounts of ozone which the dog could
Dogs can tell from the smell of a cow’s urine whether it is in oestrus, or
heat. Farmers train them to do this so they know the best time to introduce a
bull for breeding.
Dogs react in different ways to different smells. In tests, for example, it has
been found that dogs relax when the aroma of lavender is fed into their
environment. Camomile also makes dogs calmer.
Rosemary and peppermint, on the other hand, makes dogs more excited.
As far as dogs are concerned, all humans have a unique smell. They can pick
people out according to body and other odours they project. Scientists think
the only way a dog wouldn’t be able to tell two people apart would be if they
were identical twins on identical diets. The twins would also have to remain
As a result of this, dogs can track human smells over long distances.
Scientists think they can pick up on the difference in odours from different
footprints to work out which direction their prey is headed. They can do this twenty minutes after a person has passed by even though
the footprints are made a single second apart.
Scientists who tested four German Shepherds discovered they track footprints by
dividing the job into three phases. During the first, search phase they move
quickly, sniffing 10-20 times each breath. Once they have detected the smell
they enter the deciding phase where they sniff at between two and five specific
footprints. They do this for a longer period, slowing down as they do so.
Finally, once the direction has been established, the tracking phase begin with the dog once more moving quickly.
Sense: How Dogs Smell Illness
Dogs can detect cancer in
Scientists think that simply by sniffing samples of human’s breath, dogs
can detect lung, breast and other cancers with an accuracy rate of between 88
and 97 percent. The accuracy rate of a multi-million-pound hospital scanner is
between 85 and 90 per cent.
Dogs can also be trained to alert people with heart conditions they are
about to suffer a seizure.
Dogs can also anticipate in advance when a person is going to have an epileptic
A Canadian study found that dogs who lived with children prone to
epileptic episodes behaved unusually in advance of the attacks.
Some dogs would lick the child’s face or act protectively. One dog even
guided a young girl away from a set of stairs shortly before she had an attack.
The dogs’ warnings came as early as five hours before the first symptoms of the
epileptic episode were visible.
A separate study involving six dogs found that they could be trained to
accurately warn owners who were about to suffer fits.
Health authorities around the world are now training “seizure alert” or
“seizure response” dogs, some of which can predict fits, and all of which will
respond in an appropriate way when an owner does have a fit. Some will be
trained to stay with and guard the owner, and some even to press a button on a
phone which dials the emergency services.
It remains a mystery how they are able to pick up on epilepsy in this way. Some
think they pick up on tiny behavioural or scent cues. Others are convinced it
is a reaction to electrical activity in the body. But the fact that dogs also
respond to psychological seizures, which are non-epileptic and don’t display
abnormal electrical activity, casts doubt on this.