=Packing houses.=--Packing houses and abattoirs are often sources from which rats secure subsistence, especially where meats are prepared for market in old buildings. In old-style cooling rooms with double walls of wood and sawdust insulation, always a source of annoyance because of rat infestation, the utmost vigilance is required to prevent serious loss of meat products. On the other hand, packing houses with modern construction and sanitary devices have no trouble from rats or mice. =Garbage and waste.=--Since much of the food of rats consists of garbage and other waste materials, it is not enough to bar the animals from markets, granaries, warehouses, and private food stores. Garbage and offal of all kinds must be so disposed of that rats can not obtain them. In cities and towns an efficient system of garbage collection and disposal should be established by ordinances. Waste from markets, hotels, cafés and households should be collected in covered metal receptacles and frequently emptied. Garbage should never be dumped in or near towns, but should be utilized or promptly destroyed by fire. Rats find abundant food in country slaughterhouses; reform in the management of these is badly needed. Such places are centers of rat propagation. It is a common practice to leave offal of slaughtered animals to be eaten by rats and swine, and this is the chief means of perpetuating trichinæ in pork. The law should require that offal be promptly cremated or otherwise disposed of. Country slaughterhouses should be as cleanly and as constantly inspected as abattoirs. Another important source of rat food is found in remnants of lunches left by employees in factories, stores, and public buildings. This food, which alone is sufficient to attract and sustain a small army of rats, is commonly left in waste baskets or other open receptacles. Strictly enforced rules requiring all remnants of food to be deposited in covered metal vessels would make trapping far more effective. [Illustration: FIG. 5.--Guillotine trap made entirely of metal.] Military training camps, unless subjected to rigid discipline in the matter of disposal of garbage and waste, soon become centers of rat infestation. Waste from camps, deposited in covered metal cans and collected daily, should be removed far from the camp itself and either burned or utilized in approved modern ways. DESTROYING RATS AND MICE. The Biological Survey has made numerous laboratory and field experiments with various agencies for destroying rats and mice. The results form the chief basis for the following recommendations: TRAPS. Owing to their cunning, it is not always easy to clear rats from premises by trapping; if food is abundant, it is impossible. A few adults refuse to enter the most innocent-looking trap. And yet trapping, if persistently followed, is one of the most effective ways of destroying the animals.