In an unprecedented experiment, researchers at a clinic in Burlington, Mass. have transplanted brain tissue from a pig into a man who has been suffering from Parkinson's disease for 27 years. The illness kills brain cells, gradually making movement and communication increasingly difficult. Past attempts to cure human disorders with transplants from other species have failed, but doctors are hoping that the brain's weaker immune system will accept the foreign tissue. The controversial use ofhuman fetal tissuewas previously the only way to reverse the disease's course. Results of the experiment will be known in six to nine months.