Multilevel Full Mock Test 1

Part 4 
Read the following text for questions 22-30 
THE POTENTIAL TO SNIFF OUT DISEASE 
The fact diseases have a smell comes as no surprise - but finding someone or something that 
can detect them at an early stage could hold huge potential for medicine
. 
Breath, bodily odours and urine are all amazingly revealing about general health. Even the 
humble cold can give off an odour, thanks to the thick bacteria-ridden mucus that ends up 
in the back of the throat. The signs are not apparent to everyone - but some super-smellers 
are very sensitive to the odours. Joy Milne, for example, noticed her husband's smell had 
changed shortly before he was diagnosed with Parkinson's disease. 
Humans can detect nearly 10,000 different smells. Formed by chemicals in the air, they are 
absorbed by little hairs, made of extremely sensitive nerve fibres, hanging from the nose's 
olfactory receptors. And the human sense of smell is 10,000 times more sensitive than the 
sense of taste. But dogs, as the old joke might have had it, smell even better. 
Their ability to detect four times as many odours as humans makes them a potential early 
warning system for a range of diseases. Research suggesting dogs' could sniff out cancers, 
for example, was first published about 10 years ago. And there have been many tales of 
dogs repeatedly sniffing an area of their owner's body, only for it to turn out to be hiding a 

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tumour. 
What they are smelling are the "volatile molecules" given off by cells when they become 
cancerous. Some studies suggest dogs can be 93% accurate. Others suggest they can detect 
very small tumours before clinical tests can. And yet more studies have produced mixed 
results. 
Does cancer smell? 
At Milton Keynes University Hospital, a small team has recently begun to collect human 
urine samples to test dogs' ability to detect the smell of prostate cancer. The patients had 
symptoms such as difficulty urinating or a change in flow, which could turn out to be 
prostate, bladder or liver cancer. 
Rowena Fletcher, head of research and development at the hospital, says the role of the 
dogs - which have been trained by Medical Detection Dogs - is to pick out samples that 
smell of cancer. Further down the line, a clinical test will show if the dogs' diagnosis is 
correct. She says the potential for using dogs in this way is far-reaching - even if it is not 
practical to have a dog in every surgery. 
"We hope one day that there could be an electronic machine on every GP's desk which 
could test a urine sample for diseases by smelling it," she says. "But first we need to pick up 
the pattern of what the dogs are smelling." 
And that's the key. Dogs can't tell us what their noses are detecting, but scientists believe 
that different cancers could produce different smells, although some might also be very 
similar. 
 Electronic noses 
Lab tests to understand what these highly-trained dogs are smelling could then inform the 
development of 'electronic noses' to detect the same molecules. These might then give rise 
to better diagnostic tests in the future. The potential for using smell to test for a wide range 
of diseases is huge, Ms Fletcher says. 
Bacteria, cancers and chronic diseases could all have their own odour - which may be 
imperceptible to only the most sensitive humans, but obvious to dogs. It may be possible in 
the future to use disease odours as the basis for a national screening programme or to test 
everybody at risk of a certain cancer in a particular age group. 
However, there are fewer than 20 dogs in the UK trained to detect cancer at present. 

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