It seems you can still find one of these online for an exorbitant price.
The postcard was sent by Bryon (the USA).
(Pictures taken from this post.)
W. Reginald Bray. The Human Letter
The owner of the largest collection of postal curios in the British Isles, Mr. Bray was the first man to post himself as a human letter. His collection was started as a hobby in 1898; he made a thorough study of the Post Office Guide and discovered that one of the smallest articles that can be sent by post is a bee, and the largest an elephant! Mr. Bray has posted many peculiar articles, including a shirt front and a collar with the addresses actually written upon them (see illustration). Other things he has sent include a bowler hat, a turnip with the address and message carved on it, a pipe, a cigarette, flask, shoes, cycle pump, etc.