Bratting is therefore the best preventive, and it is as cheap as it is effectual. One pair of old blankets, worth only some four or five shillings, will furnish coverings for forty hogs, and if laid carefully aside in spring, they will continue serviceable for two or three years. An operation can avail nothing--slaughtering the sheep is therefore the only expedient. When the existence of a hydatid near the surface of the brain is denoted by the skull yielding, at some particular spot, to the firm pressure of the thumb, its extraction must be set about in the manner described in paragraph (118), where I have also given my objections to the common modes of operating. (171.) _Trembling._ Several affections are included under the name of _trembling_ or _leaping-ill_, all having, in common, more or less of the symptoms which these names denote. They may be considered as arising from exposure to cold and damp, especially on long fatiguing journies, as in bringing sheep from the Highlands to the south of Scotland, when it frequently prevails to so great an extent, on reaching the low country, as to oblige the shepherd to leave eight or ten behind him at every stage. Injuries of the loins, either inflicted by themselves in jumping and running, or by others from rough usage in the fold, are common causes of the disease; but in this variety the hind quarters only are powerless. Another species is owing to oppression of the brain from congestion, in this way resembling incipient sturdy, and occurring only in very fat sheep. (172.) _Treatment of Trembling._ The first variety is best met by rest, shelter, and a supply of nutritious food; but as the animal is incapable, in many cases, of collecting it, the shepherd must lift it from one rich part of the field to another, so soon as it has cleared away the grass within its reach. In the second kind, as caused by accident, the sheep must be slaughtered, as, should a cure be attempted, the treatment will be too tedious and complicated to succeed in ordinary hands. Copious blood-letting, and doses of Epsom salts, will be found of most advantage in the third species; but if the sheep can be disposed of so much the better, as this kind of _trembling_ is almost certain, unless combated by energetic depletion, to end in sturdy. (173.) _Wood Evil_ is nothing more than a cramp of the hind legs, owing to water dripping upon them from trees after a shower of rain, and is best treated by enveloping them in flannel, wrung out of hot water; but if the sheep is at the time very chill, gentle friction must first be used, else dangerous consequences will ensue. Rubbing with warm turpentine has been recommended, and is apparently worthy of a trial.