A source of valuable stem cells BURGER/PHANIE/SCIENCE PHOTO LIBRARY

A healing balm for the brain? Infusions of umbilical cord blood seem to help people recover better after a stroke.

Strokes occur when blood can’t reach brain cells because of a blocked or burst blood vessel, causing them to rapidly starve and die. Joanne Kurtzberg at Duke University, North Carolina, and her colleagues wondered if young blood might help heal brains that have been damaged in this way.

Blood from babies and teenagers has previously been shown to reverse brain ageing in older mice, and there are hints that young …