Inoculation (also known as variolation) was a historical method for the prevention of smallpox by deliberate introduction into the skin of material from smallpox pustules. This generally produced a less severe infection than naturally-acquired smallpox, but still induced immunity to it. The term entered medical English through horticultural usage meaning to graft a bud (or eye) from one plant into another. It is derived from the Latin in + oculus (eye). Though innoculation/innoculate is sometimes seen, this is incorrect, possibly erroneously thought to be related to innocuous, which is derived from the Latin in + nocuus (not harmful).