Quoting from "Walden"

One farmer says to me, "You cannot live on vegetable food solely, for it furnishes nothing to make bones with"; and so he religiously devotes a part of his day to supplying his system with the raw material of bones; walking all the while he talks behind his oxen, which, with vegetable-made bones, jerk him and his lumbering plow along in spite of every obstacle. -- Henry David Thoreau