A s far back as 400 BC, Hippocrates advised his students to smell their patients’ breaths to detect if they were ill. Now, researchers in America have invented a system which does just that, only rather more scientifically. A new analyser uses nano-rays to determine the precise chemical composition of a person’s breath. From that it is able to detect the “signature” of any of 17 serious diseases, from kidney cancer to Parkinson’s disease. Exhaled breath contains nitrogen, carbon dioxide and oxygen, as well as small amounts of more than 100 other chemicals, but the relative amount of each substance...