This section is from the book "The Steward's Handbook And Guide To Party Catering", by Jessup Whitehead. Also available from Amazon: Larousse Gastronomique.
The sea-slug or trepang or sea cucumber; a kind of sea caterpillar of considerable importance to the Asiatics, who eat it and trade in it dried. It is from 8 to 15 inches long and abundant on the Florida reefs. At Key West an enterprising yankee went into the business of making trepang- (dried beche de mer) a few years ago, but he did not succeed in making it pay. (See Chinese Cookery).
"With reference to that prime Celestial delicacy, the beche de mer, or sea-slug, it may be of interest to describe the method of making the soup as I have seen it prepared by several good Chinese cooks. For, say, ten persons make soup in the ordinary way, of beef, etc. Take two teat fish (sea-slugs) of good quality, or a corresponding quantity of black or red fish, soak in water from 12 to 24 hours, thoroughly scrape and clean from time to time, changing the water as required, as it swells greatly. The result will be a glutinous-looking mass, like lumps of jelly. Boil separately for five or six hours; take out and cut or mince Dp very fine. About a quarter of an hour before serving add this to the soup and let it boil. There must not be any vegetables.. Mince or egg balls are a desirable addition, also shcrrv, etc., to taste. This gives a body to the soup, which, if left over, will be almost a jelly when cold. I believe if the beche de mer were understood it would be used all over the world, especially for invalids, as it is very strengthening, and, although anything but nice-looking in its dry state, it is a very delicate article of diet when properly treated. It makes a splendid addition to beef tea, and I would call the attention of medical men to this fact.
In the form of soup it is frequently used in the clubs and leading hotels in Melbourne and Sydney".