One of the first proofs of the perishing of a brick drain, making it past redemption, is the appearance of rats. Rats will go always to that place which affords them most food; and it is the brick barrel drain which receives the washings from meat plates, and the grease from the scullery pots, which rats most commonly frequent. They will leave a drain, and nest themselves in the thatched roof of a farmhouse, and they will form whole villages under the floors of a town house. Rats generally find their way into houses by means of holes which have been formed in brick drains by the falling down of perished bricks from the arch, or owing to their having contrived to make a passage through the brick drain above the usual wetted perimeter. These rats, in the case of country houses, may come from the stables, the barns, or the brooks; but in town houses they chiefly emanate from the sewer. No matter whence originally derived, they soon become habituated to a house and its dainty scraps, and having once engineered their way thither, are seldom effectually dislodged, especially in country residences. As fast as a hole is discovered and stopped up, another is made by these persistent vermin, until the foul air evolved from the house drain becomes so distressful, and the rats so multiply, that some further steps are necessary in dealing with them. Where the evil has not yet grown formidable, traps are made use of, or poison; but this last is a dangerous resource, as the rats are apt to die underground and emit during decomposition, which lasts for months, the most horrible smells. It may be added that rats are remarkably clean animals, and will never allow their fur to come in contact with anything that cannot easily be immediately cleaned from it; hence, very often a dairy, larder, or granary is surrounded by a trench outside the brick walling to a certain depth, by broken glass and gravel, well grouted with tar. Never rely upon a siphon trap in the drain, as a means of keeping out these voracious and fast-breeding animals. They will eat even through lead pipes ⅛ inch in thickness.