Professor Roger Smith uses ultrasound to monitor the progress of an injection of stem cells into the injured foreleg of a racehorse at the Royal Veterinary College, North Mymms, north of London, April 17, 2007. Stem cell therapy may be controversial in human medicine but in the world of horse racing it is becoming the odds-on favourite for tackling tendon damage, which accounts for one in three racecourse injuries. Picture taken April 17, 2007. To match feature STEMCELLS-HORSES/ REUTERS/Ben Hirschler/Files (BRITAIN)