Though beavers were once abundant in the Northern Hemisphere, extensive hunting of the animals for their fur and musk glands caused them to be eradicated from much of their range by the mid-1800s. The liquid exuded by the musk glands, called castoreum, was sought for medicinal use and perfumes, while the thick, lush fur was highly valued for hats and other apparel. Indeed, beaver was such a fundamental commodity in colonial America that their skins became a unit of measure, traders using them as a sort of money that could be used to purchase a certain number of other goods. Despite the continued demand for beaver fur and other products, however, in recent years, the aquatic animals have regained much of their former range due to limitations placed on hunting and reintroduction efforts.