This section is from the book "The Dogs Of Great Britain, America, And Other Countries. Their Breeding, Training, and Management in Health and Disease", by John Henry Walsh (Stonehenge). Also available from Amazon: The Dogs Of Great Britain, America And Other Countries.
With the exception of the greyhound, sporting dogs require some considerable education for the sport in which they are to be engaged. Unlike the hound and the dogs intended for the gun, greyhounds have only their instinctive desires to be developed, and as no restraint is at any time placed upon these, except that depend-ing upon mechanical means which they cannot get rid of, nature has uncontrolled sway. Hence their entering is a very easy process; nevertheless, there are some precautions to be taken which it is necessary to describe. The deerhound, as well as the greyhound, is held in slips, a single one being used for him, and a double slip, or pair or slips as it is called, for the two greyhounds which form the complement for coursing the bare - a greater number being considered unfair, and therefore unsportsmanlike. These slips are so made that by pulling a string the neck-strap is loosed, and the two dogs are let go exactly at the same moment. They are always used in public coursing, but in private the greyhounds are sometimes suffered to run loose, waiting for the moment when the hare is put up by the beaters or by the spaniels, which are occasionally employed.
Hounds also are coupled under certain circumstances, but they are never slipped at the moment when game is on foot, and they must therefore be made steady from "riot."