is a most necessary precaution.

Old buildings in cities.—Aside from old dwellings, the chief refuges for rats in cities are sewers, wharves, stables, and outbuildings. Modern sewers are used by the animals merely as highways and not as abodes, but old-fashioned brick sewers often afford nesting crannies.

Fig. 2.—Rat-proofing a frame dwelling by concrete side wall (United States Public Health Service, New Orleans, La., 1914).

Wharves, stables, and outbuildings in cities should be so built as to exclude rats. Cement is the chief means to this end. Old tumble-down buildings and wharves should not be tolerated in any city. (See fig. 2.)

In both city and country, wooden floors of sidewalks, areas, and porches are commonly laid upon timbers resting on the ground. Under such floors rats have a safe retreat from nearly all enemies. The conditions can be remedied in towns by municipal action requiring that these floors be replaced by others made of cement. Areas or walks made of brick are often undermined by rats and may become as objectionable as those of wood. Wooden floors of porches should always be well above the ground.

Farm buildings.—Granaries, corncribs, and poultry houses may be made rat-proof by a liberal use of cement in the foundations and floors; or the floors may be of wood resting upon concrete. Objection has been urged against concrete floors for horses, cattle, and poultry, because the material is too good a conductor of heat, and the health of the animals suffers from contact with these floors. In poultry houses, dry soil or sand may be used as a covering for the cement floor, and in stables a wooden floor resting on concrete is just as satisfactory so far as the exclusion of rats is concerned.

The common practice of setting corncribs on posts with inverted pans at the top often fails to exclude rats, because the posts are not high enough to place the lower cracks of the structure beyond reach of the animals. As rats are excellent jumpers, the posts should be tall enough to prevent the animals from obtaining a foothold at any place within 3 feet of the ground. A crib built in this way, however, is not very satisfactory.

For a rat-proof crib a well-drained site should be chosen. The outer walls, laid in cement, should be sunk about 20 inches into the ground. The space within the walls should be grouted thoroughly with cement and broken stone and finished with rich concrete for a floor. Upon this the structure may be built. Even the walls of the crib may be of concrete. Corn will not mold in contact with them, provided there is good ventilation and the roof is water-tight.

However, there are cheaper ways of excluding rats from either new or old corncribs. Rats, mice, and sparrows may be kept out effectually by the use of either an inner or an outer covering of galvanized-wire netting of half-inch mesh and heavy enough to resist the teeth of the rats. The netting in common use in screening cellar windows is suitable for covering or lining cribs. As rats can climb the netting, the entire structure must be screened, or, if sparrows are not to be excluded, the wire netting may be carried up about 3 feet from the ground, and above this a belt of sheet metal about a foot in width may be tacked to the outside of the building.

Complete working drawings for the practical rat-proof corncrib shown in figures 3 and 4 may be obtained from the Office of Public Roads and Rural Engineering of the department.

Buildings for storing foodstuffs.—Whenever possible, stores of food for man or beast should be placed only in buildings of rat-proof construction, guarded against rodents by having all windows near the ground and all other possible means of entrance screened with netting made of No. 18 or No. 20 wire and of ¼-inch mesh. Entrance doors should fit closely, should have the lower edges protected by wide strips of metal, and should have springs attached, to insure that they shall not be left open. Before being used for housing stores, the building should be inspected as to the manner in which water, steam, or gas pipes go through the walls, and any openings found around such pipes should be closed with concrete.

Fig. 3.—Perspective of rat-proof corncrib, showing concrete foundation by dotted lines; also belt of metal.

If rat-proof buildings are not available, it is possible, by the use of concrete in basements and the other precautions just mentioned, to make an ordinary building practically safe for food storage.

When it is necessary to erect temporary wooden structures to hold forage, grain, or food supplies for army camps, the floors of such buildings should not be in contact with the ground, but elevated, the sills having a foot or more of clear space below them. Smooth posts rising 2 or 3 feet above the ground may be used for foundations, and the floor itself may be protected below by wire netting or sheet metal at all places where rats could gain a foothold. Care should be taken to have the floors as tight as possible, for it is chiefly scattered grain and fragments of food about a camp that attract rats.

Rat-proofing by elevation.—The United States Public Health Service reports that in its campaigns against bubonic plague in San Francisco (1907) and New Orleans (1914) many plague rats were found under the floors of wooden houses resting on the ground. These buildings were made rat-proof by elevation, and no case of either human or rodent plague occurred in any house after the change. Placing them on smooth posts 18 inches above the ground, with the space beneath the floor entirely open, left no hiding place for rats.

This plan is adapted to small dwellings throughout the South, and to small summer homes, temporary structures, and small farm buildings everywhere. Wherever rats might obtain a foothold on the top of the post they may be prevented from gnawing the adjacent wood by tacking metal plates or pieces of wire netting to floor or sill.

KEEPING FOOD FROM RATS AND MICE.

The effect of an abundance of food on the breeding of rodents should be kept in mind. Well-fed rats mature quickly, breed often, and have large litters. Poorly fed rats, on the contrary, reproduce less frequently and have smaller litters. In addition, scarcity of food makes measures for destroying the animals far more effective.

Merchandise in stores.—In all parts of the country there is a serious economic drain in the destruction by rats and mice of merchandise held for sale by dealers. Not only foodstuffs and forage, but textiles, clothing, and leather goods are often ruined. This loss is due mainly to the faulty buildings in which the stores are kept. Often it would be a measure of economy to tear down the old structures and replace them by new ones. However, even the old buildings may often be repaired so as to make them practically rat-proof; and foodstuffs, as flour, seeds, and meats, may always be protected in wire cages at slight expense. The public should be protected from insanitary stores by a system of rigid inspection.