Washington, D.C ? Initial tests indicate an experimental vaccine for ricin works and is safe, raising the possibility it might one day offer protection from a poison that authorities fear could be a weapon for terrorists.

Deadly and easy to produce, ricin is extracted from castor beans. It can be added to food or water, injected or sprayed as an aerosol.

Researchers led by Dr. Ellen Vitetta of the University of Texas Southwestern Medical Center in Dallas found a way to modify the toxic sections of the ricin molecule to disrupt its poisonous effect.

Their findings were reported Monday in the online edition of Proceedings of the National Academy of Sciences.

The new molecule, called RiVax, was given to mice and rabbits, which then developed antibodies and those antibodies protected the animals when they were later given doses of ricin.