Thanks to the 220 million cells in a dog's nose that detect odors, compared to 5 million in people, a pooch can sniff out serious diseases, even without the benefit of a medical degree.  Cancerous tumors emit slight smells that dogs can pick up and recognize as something bad, even picking up a single chemical or a combination of them. Dogs trained to detect illness who were tested were right 99 per cent of the time. That's almost as good as this guy.