Rat, or Mus, L. a genus of quadrupeds, comprising 60 spe-cies, of which the following are the principal:

1. The decumanus, Brown or Water Rat, which is a native of the East Indies; whence it has, within the last century, been introduced into Europe by the ships re-turning from that country. The head and body are about nine inches in length, the upper parts being of a light-brown cast, intermixed with a tawny or ash-colour : its naked scaly tail consists of 200 rings, and measures from seven to eight inches in length.

Water-rats inhabit holes which they burrow near the banks of rivers and pools, and which are provided with two apertures; one being above ground among the grass, while the other is concealed beneath the surface of the water. As they will forsake the situation, if they cannot bide their upper ave-nue among weeds, etc. Dr. Darwin is of opinion, that they may be driven away by keeping the rim or margin round fish-ponds so low, as to rise only two, three, or at most four inches above the level of the water ; and also by eradicating high grass and weeds. These ani-mals, however, infest drains, aque-ducts, stables, barns, gardens, and houses, as well as rivers; they swim and dive very dexterously ; commit great depredations on ve-getables, grain, fruits, and even poultry; nay, they sometimes at-tack and eat living pigs. Considerable stores of acorns, beech mast, and other articles, are often found in their holes, as a provision for the winter, during which the males live by themselves, while the females, and young rats subsist in barns, out-houses, and similar buildings.

Being uncommonly prolific, the water-rat produces from 12 to 19 young at a litter ; and, when unable to procure food from a parti-cular spot, they migrate, in large companies, to towns and villages, where they disperse themselves in - different dwellings, and devour the common or house-rat. These creatures are so fierce and intrepid, that they will even resist, and bite their pursuers, inflicting dangerous wounds, which are attended with great inflammation, and not easily healed.

2. The rattus, Black or Com-mon Rat, is a native of Europe, and Asia, whence it has been con-veyed in ships to Africa and America. Its head and body are seven inches long ; the back is of a deep blackish-grey, and the lower parts of an ash-colour ; the tail is very thin and scaly, consisting of 150 rings, and measuring 8 inches in length. These animals have, since the introduction of the water-rat, considerably decreased in some parts of Europe, and in a few places have entirely been exterminated ; but they still abound in Britain, where they continue to multiply ; though different expedients are constantly employed for their extermination. The female is furnished with ten teats, and brings forth several times in the year, from five to six at a litter.

The common rat inhabits barns, granaries, and houses ; in the latter of which it forms nests, between the floors and ceilings, as well as in the vacant spaces between the wainscot and wall. From these recesses, they-sally forth in search of food, devouring meat, paper, corn, clothes, poultry, game ; and even gnawing the extremities of infants, when asleep : instances have occurred, where these vermin have increased to such an alarming degree, that the inhabitants have been compelled to abandon their houses.

On account of the extensive damage occasioned by both these predatory species, various methods of extirpating them are practised, with greater or less success. Dogs, cats, forrets, and weazels, are their natural enemies; and, though such useful animals destroy great numbers, yet the killing or taking of rats furnishes employment to many skilful men, who pursue different ways of catching them ; and who are known under the name of Rat-catchers.

Bats are often caught in traps baited with burnt leather, or toast-ed cheese ; but a more efficacious method of destroying them, consists cists in mixing a quart of oatmeal with six drops of oil of rhodium, one grain of musk, and two or three fruits of the nux vomica finely pulverized; and forming the whole into pellets, which must be placed near their holes. This recipe was first published in the Letters of the Bath Society, where it is observed, that the rats ate eagerly at first, and that great numbers were killed ; but, after a short time, they declined to devour it. Hence, a more alluring substitute was recommended, namely, three parts of oatmeal, and one of staves-acre, made into a paste with honey, which should be divided into small pieces, and laid at the entrance of their avenues.

Another composition has been made of wheaten flour, sugar, and water,. kneaded into a paste, and scented with a few drops of oil of caraway-seeds : small portions are to be exposed at stated times near their holes, till the animals, lulled into security, collect in considerable numbers. It will then be advisable to incorporate a sufficient quantity of arsenic, finely levigated, with the paste, and thus to render it a fatal poison for mice and rats.

Toward the close of the year 1800, Mr. Cundell obtained a patent for a new compound invented by him, with a view to destroy rats.- He directs eight ounces of calomel to be mixed with fourteen ounces of dried and pulverized solanum (night-shade) ; fifty-six pounds of oatmeal ; six pounds of melasses, and a sufficient quantity of oil of rhodium, to communicate a fragrant smell : the whole is to be formed into a mass with sweet oil.

Beside these remedies, there are many other contrivances for exterminating rats : and, as the subject is of considerable importance to every house-keeper, we shall sub-join an account of several other means, which have been found re-markably successful.

Mr. Charles Taylor, Secretary to the Society for the Encouragement of Arts, etc. directs one or two table-spoonfuls of dry oatmeal to be uniformly, but thinly, spread on a tile or plate, in order that the quantity taken away may be more easily ascertained. The rats, if not interrupted, will regularly feed there; and they must be supplied for two or three successive days with fresh meal, when three drops of oil of aniseed are to be mixed with a double portion of oatmeal ; and the composition deposited at the usual place, for a similar period of time. On the fourth day, one half only of the usual quantity must be given of the scented preparation, and on the succeeding night, the following mixture must be placed at the hole : - Let four ounces of dry oatmeal, perfumed with six drops of the oil of aniseed, be thoroughly incorporated with half an ounce of carbonated barytes (aerated heavy spar of Derbyshire), which has been previously pulverized, and sifted through fine cambric or muslin. This compound must be spread on the tile or slate, and exposed as usual ; all the doors, or other communications, being shut for the space of 24 hours, that the vermin may eat it undisturbed by any cats, dogs, or other animals; and also to prevent the possibility of any accident happening to the latter. In the course of a few hours, after the rats have eaten the composition, they will be seen frequently to reel about, as if they were intoxicated, or paralytic; though, at length, they return to their haunts, and perish. Mr. Tay-lor observes that, as they are very cunning, the mixture ought to be left for 48 hours, in case a small portion only be eaten; after which time the remainder should be burnt.

Mr. Funke, in his valuable Na-tural History, calculated for German Schools, communicates the following curious method of expel-ling, or rather dispersing, rats from dwelling-houses : - Take one or more of these predatory creatures caught alive in a trap, and immerse them to the neck in a mixture con-sisting of equal quantities of tar and train oil : thus anointed, set the animals at liberty. The offensive smell of this preparation compels them to traverse all the holes - of their companions with the most distressing anxiety; inconsequence of which they collectively disap-pear.—Another expedient practised in Germany, is that of confining a live rat in a cage, and feeding it exclusively with living mice or rats. Having been for some time accustomed to such food, the captive animal is, after a short fasting, suffered to return to its former habitation, where it is said to persecute, and indiscriminately devour its own species.

M. Gaschitz, one of the most esteemed German writers on eco-nomy, states the following to be an effectual remedy for destroying not only moles and mice, but also rats infesting orchards, and injuring the roots of fruit-trees :- Boil a number of fresh walnuts divested of their external green rind, for an hour and half in water ; to which a large handful of hemlock leaves has previously been added. As all these vermin are extremely fond of such nuts, place one of the latter thus prepared within the cavity of every mole-hill. Those which partake of this envenomed fruit, must inevitably perish. The same author advises gardeners to plant a single clove of garlic near every tree; in consequence of which simple practice, neither mice nor rats will approach it. He ob-serves, that the strong odour of this bulbous root is probably offensive to their organs of breathing ; and, whatever be the cause, he pledges himself for the success of the ex-periment.

In Sweden, the green branches of the Bird-Cherry (Prunus Padus, L) are successfully employed for the dispersion of rats, moles, and bugs, when placed in the corners of granaries, stables, dwelling-houses, and mole-hills ; but it will be necessary to re-place the dry sprigs, once a week, or fortnight, with fresh branches.

Among other remedies, we recommend that commonly employed on the Continent, where a sponge is fried with salt-butter in a pan ; then compressed between two plates ; and cut into small pieces, which are scattered about the holes frequented by ruts and mice. This preparation is devoured with avidity ; it excites thirst in the animals, which should be gratified, by exposing shallow vessels containing water. On drinking this fluid, after having swallowed the burnt sponge, it distends their stomach, and proves a fatal repast.

M. v. d. HOrst, a landed proprietor in Germany, has lately announced in one of the public jour-nals, that a peacock kept in a poultry-yard, or about the premises of a dwelling-house infested with rats and mice, is an excellent scarecrow against such free-bootcrs : nay, he remarks, that even a cock of an early spring-brood, has so shrill and penetrating a voice, as to answer the same purpose. With regard to the former bird, he appeals to his own experience, which has furnished him with satisfactory proofs of success.

Lastly, as most of the methods before suggested, are either troublesome and precarious, or only partial means of exterminating the object of our research, we shall conclude with a more general and summary process of entrapping rats, so as to deliver not only our own habitations, but those of our neighbours, from the incursions of such mischievous quadrupeds. For the discovery of the following complete remedy, we are indebted to G. W. Muller, an ingenious apothecary of Wernigerode, in Germany : he candidly acknowledges to have derived the first hint for such purpose, many years since, from a book written by a cele-brated economist ; in short, it will be found the most expeditious and effectual mode that can be pur -sued.- A capacious cask of moderate height must previously be procured, and put in the vicinity of places infested with rats. During the first week, this vessel is employed only to allure the rats to visit the solid top of the cask, by means of boards or planks arranged in a sloping direction to the floor, which are every day strewed with oatmeal, or any other food equally grateful to their palate; and the principal part of winch is exposed on the surface. After having thus been lulled into security, and accustomed to find a regular supply for their meals, a skin of parchment is substituted for the wooden top of the cask, and the former is cut, for several inches, with transverse incisions through the centre, so as to yield on the smallest pres- sure. At the same time, a few gallons of water, to the depth of five or six inches, are poured into the empty cask. In the middle of this element, a brick or stone is placed, so as to project one or two inches above the fluid ; and that one rat may find on the former, a place of refuge. These preparatory measures being taken, the boards as well as the top of the cask should now be furnished with proper bait, in order to induce them to repeat their visits. No sooner does one of these marauders plunge through the section of the parchment into the vessel, than it retreats to the brick or stone, and commences its lamentations for relief. Nor are its whining notes uttered in vain: others soon follow, and share the same fate; when a dreadful conflict begins among them, to decide the possession of the dry asylum. Battles follow in, rapid succession, attended with such loud and noisy shrieks, that all the rats in the neighbourhood hasten to the fatal spot, where they experience similar disasters. Thus, hundreds may be caught by a stratagem, which might be greatly facilitated by exposing a living rat taken in a trap, or purchased from a professional rat-catcher.-Nay, if it be true, that a whole inhabitable island on the western coast of Scotland be infested with these destructive vermin, we are of opinion, that they could thus be speedily exterminated ; and that the carcasses of such animals as have hitherto been considered as useless, might be advantageously employed for the purposes of ma-nuring the barren soil of those inhospitable regions.

Rat. - A patent was lately granted to Mr. Bosquet, for his method of preventing the nuisance, and pernicious effects of rats, on ship-board, etc. This important object is to be attained, by filling up the vacant spaces between the planks, lining, and timber of ships, with hot or melted pitch, tempered with a little tar, to render it less brittle, and more tenacious : at the same time, to increase its adhesion and durability, the patentee directs cork-shavings, charcoal-dust, and ox or other animal hair, to be incorporated with the composition. By such contrivance, all rats will not only be effectually repelled, and consequently the destructive effects of these vermin living, breeding, dying, and rotting between the ship's timber, be avoided, but the safety of the vessel will also be ensured : for, in case a plank should start, he asserts, that no water can penetrate through the composition.

The following preparation has also recently been recommended for expelling rats: it consists in mixing the expressed juice of the stalk or leaves of the Deadly Nightshade with wheaten flour, or oatmeal : the paste must be cut in small pieces, which are to be placed in the holes or tracks frequented by these depredators ; and, though they will not eat such nauseous food, yet its odour is to them so extremely offensive, that they will speedily quit the premises.