The rat is one of the most despised and tormented of created animals; he has many enemies and very few friends; wherever he appears his life is in danger from men, dogs, cats, owls, &c., who will have no mercy on him. These perpetual persecutions oblige him to be wary in his movements, and call for a large amount of cunning and sagacity on his part, which give his little sharp face a peculiarly knowing and wide-awake appearance, which the most superficial observer must have noticed. Though, poor creature, he is hated and killed by man, his sworn foe, yet he is to that same ungrateful race a most useful servant, in the humble capacity of scavenger; for wherever man settles his habitation, even in the most remote parts of the earth, there, as if by magic, appear our friends the rats. He quietly takes possession of the out-houses, drains, &c., and occupies himself by devouring the refuse and filth thrown away from the dwelling of his master (under whose floor, as well as roof, he lives); this refuse, if left to decay, would engender fever, malaria, and all kinds of horrors, to the destruction of the children of the family, were it not for the unremitting exertions of the rats to get rid of it, in a way no doubt agreeable to themselves, namely, by eating it. The rat is admirably armed and equipped for the peculiar mode of life which he is ordained to lead. He has formidable weapons in the shape of four small, long, and very sharp teeth, two of which are fixed in the upper and two in the under jaw. These are formed in the shape of a wedge, and by the following wonderful provision of Nature, have always a fine, sharp, cutting edge. On examining them carefully, we find that the inner part is of a soft, ivory-like composition, which may be easily worn away, whereas the outside is composed of a glass-like enamel, which is excessively hard. The upper teeth work exactly into the under, so that the centres of the opposed teeth meet exactly in the act of gnawing; the soft part is thus being perpetually worn away, while the hard part keeps a sharp, chisel-like edge; at the same time the teeth grow up from the bottom, so that as they wear away a fresh supply is ready. The consequence of this arrangement is, that, if one of the teeth be removed, either by accident or on purpose, the opposed tooth will continue to grow upward; and, as there is nothing to grind it away, will project from the mouth and be turned upon itself; or, if it be an under-tooth, it will even run into the skull above.