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The tracking down of
criminals - and in particular escaped convicts - by means of sniffer dogs is
a method of identification so antique as to have entered the classic tales of
Dickens and Conan Doyle, and the folklore of American slavery. Indeed, the term
'bloodhound' has frequently been applied to the dogs' human counterpart, the
pertinacious - or 'dogged' - detective.
Dogs are well known for their superior sense of smell, and the bloodhound was
developed especially for tracking human beings. This depends, of course, on the
fact that every person leaves behind them an invisible odour trail that is as
unique in its way as a
fingerprint, and the dog only needs a whiff of a 'control' object, such as
an item of clothing worn by the fugitive, to pick up an unerring path to its
quarry.
The curiously old-fashioned concept of man's best friend as an arm of the law
has recently been revised, and the hounds remarkable powers of scent have been
specially trained to assist customs officers and drug enforcement agencies to
sniff out narcotics, and in the ceaseless battle against terrorism to locate
explosives and firearms. Dogs have even been trained to search for dead bodies,
and although the animals are often brought in to assist in murder hunts where a
body has not been found, their greater use is in the location of victims of
earthquakes and transport disasters.
However, there are other ways in which smell can be used to trap a
criminal - not by tracking him (after all in the modern world a scent will
be lost as soon as the fugitive drives off in a car) but by identifying him much
as one would with a
fingerprint. But unlike the
fingerprint, which can be masked with the use of gloves, or to use a
disguise to defeat visual identification, nothing can be done to hide smell. It
follows that if some means could be devised of storing and analyzing that smell
left at the
scene of the crime for future comparison it would be a most useful addition
to the crime-fighters arsenal.
Not surprisingly the possibility of designing an 'electronic-nose' has already
been under investigation for some years, notably by the Olfaction Research Group
at the University of Warwick. The first requirement is to understand exactly
what it is that an animal's nose does.
The nose reacts to volatile chemicals in the atmosphere which are then analyzed
by the brain which identifies molecules of different shapes and dimensions which
relate to individual smells. An experimental instrument is already being tested
consisting of twelve tin oxide sensors each of which responds in a slightly
different way. The electrical outputs construct between them a pattern which can
be expressed graphically on a VDU screen. The 'artificial-nose' has already
proved capable not only of distinguishing wines and coffee, but between
different wines and different coffees. To add a slightly more Sherlockian air,
it can also distinguish between the smells of different cigarettes and cigars.
The problem is that the human body odour is infinitely more complex, and subject
not only to the many pollutions in the atmosphere and applied cosmetics,
deodorants, etc., but is modified by what the body eats and drinks. It has been
discovered, however, that behind all this confusion there is a unique
identifiable 'smell'. |
