The rats have been for a long time the pests of these gardens, attracted by the presence of large quantities of food. The grating under one of the tigers' dens is eaten through by this nimble-toothed burglar, who makes as light of copper wire as of leaden pipes. Immediately upon the construction of the new monkey-house, they took possession, and eat through the floors in every direction to get at poor Jacko's bread. Vigorous measures were taken to exclude them; the floors were filled in with concrete, and the open roof was ceiled; but they quickly penetrated through the plaster of the latter, as may be seen by the holes to this day. They burrowed in the old inclosure of the wombat till the ground was quite rotten; and they still march about the den of the rhinoceros and scamper over his impregnable hide. It is only by constantly hunting them with terriers that they can be kept down; and as many as a hundred in a fortnight are often despatched, their carcases being handed over to the vultures and eagles. Many of them seek in the daytime a securer retreat. They have frequently been seen at evening swimming in companies across the canal to forage in the gardens through the night, and in the morning they returned to their permanent quarters by the same route. The proprietors of the bonded-wheat warehouses on the banks of the Thames are forced to take the utmost precautions against the entrance of these depredators; otherwise, they would troop in myriads from the sewers and waterside premises, and, as they are undoubtedly in the habit of communicating among their friends the whereabouts of any extraordinary supplies, they would go on increasing day by day as the report of the good news spread through rat-land. To repel their attentions, the wooden floors and the under parts of the doors of the granaries are lined with sheet-iron, and the foundations are sometimes set in concrete mixed with glass--matters too hard for even their teeth to discuss. Country rats in the summer take to the fields, and create enormous havoc among the standing corn. They nibble off the ears of wheat, and carry them to their runs and burrows, where large stores have been found hoarded up with all the forethought of the dormouse. Farmers are often puzzled to account for the presence of rats in wheat stacks which have been placed upon the most cunningly-contrived stands. The fact is, these animals are tossed up with the sheaves to the rick, where they increase and multiply at their leisure, and frequently to such an extent, that a rick, seeming fair on the outside, is little better than a huge rat-pie. The propensity of the rat to gnaw must not be attributed altogether to a reckless determination to overcome impediments. The never-ceasing action of his teeth is not a pastime, but a necessity of his existence. The writer of an interesting paper on rats in _Bentley's Miscellany_ has explained so clearly the dentistry of the tribe, that we extract his account:--