Substances that cannot cross this barrier are unlikely to make effective treatments for a brain disease.

ECONOMIST: Creutzfeldt-Jakob disease

Some of these viruses have also been reported to cross the species barrier and cause disease or sub-clinical infections in humans.

FORBES: Bird Flu Claims More Lives In Shanghai

One group of researchers has thus decided to cross the species barrier and test its models on another highly social mammal, the dolphin.

ECONOMIST: What maths tells us about us

The New York Post is the latest newspaper to cross the iPad barrier, with a new, full-content tablet edition readers will be able to purchase as a monthly or annual subscription.

FORBES: New York Post to Sell Subscriptions on the iPad

If Democrats can cross the psychic barrier of accepting that universal coverage is just not viable now, they'll see there's a much safer, surer and politically beneficial course wide open for them: Just call the Republicans' bluff about starting over.

FORBES: Dangerous Thoughts

Mr Schwartz is a former director of the Institut Pasteur in France, and his book maps out with great clarity the scientific investigation into how scrapie a disease that has long been known to afflict sheep came to cross the species barrier to cows, and then from cows to humans.

ECONOMIST: Food safety

The road will cross a small stream and continue parallel to the stream for some time before the first blue cross appears on the side barrier of a small cement bridge.

BBC: Romania��s Prince Charles walk

"There used to be this barrier between the States and the UK - a border you couldn't cross, " he told the BBC.

BBC: Brits 2013: The real winners and losers