It was not until the end of the 18th century that Joseph Priestley accidentally discovered the ability of plants to "restore" air that had been "injured" by the burning of a candle. He followed up on the experiment by showing that air "restored" by vegetation was "not at all inconvenient to a mouse." He was later awarded a medal for his discoveries that "...no vegetable grows in vain... but cleanses and purifies our atmosphere." Priestley's experiments were further evaluated by Jan Ingenhousz, a Dutch physician, who then showed that the "restoration" of air only worked while in the presence of light and green plant parts.