FOOD AND SHELTER are as essential to rats as toother animals, and the removal of these offers apractical means of permanent rat control. The numberof rats on premises and the extent of their destructivenessare usually in direct proportion to theavailable food supply and to the shelter afforded.Rat proofing in the broadest sense embraces not onlythe exclusion of rats from buildings of all types butalso the elimination of their hiding and nesting placesand cutting off their food supply. Through opendoors and in other ways, rats may frequently gainaccess to structures that are otherwise rat proof, butthey can not persist there unless they find safe retreatsand food. When rat proofing becomes theregular practice the rat problem will have beenlargely solved.