SLEEPERS, in Natural History, a name given to those animals which sleep all winter, such as bears, marmots, dormice, bats, hedgehogs, swallows, and the like. These do not feed in winter, have no sensible evacuations, breathe little or none at all, and most of the viscera cease from their functions. Some of these animals seem to be dead, and others return to a state like that of the fetus before birth. In this state they continue, till, by an increase of heat, the animal is restored to its former functions.