On taking leave, Livingstone promised to bear his instructor in mind if any curiosity fell in his way.

Years passed, and as no communication reached him, Mr.
Owen was disposed to class the promise with too many others made in the like circumstances.

But on his first return to this country Livingstone presented himself, bearing the tusk of an elephant with a spiral curve.
He had found it in the heart of Africa, and it was not easy of transport.

"You may recall," said Professor Owen, at the Farewell Festival in 1858, "the difficulties of the progress of the weary sick traveler on the bullock's back.

Every pound weight was of moment; but Livingstone said, 'Owen shall have this tusk,' and he placed it in my hands in London." Professor Owen recorded this as a proof of Livingstone's inflexible adherence to his word.