One of its chief characteristics is the power it possesses of producing a substance termed "castor,"--which is contained in two bags, each about the size of a hen's egg.  This castor is peculiarly attractive to beavers.  They scent it at a distance, and invariably make their way towards it.  No sooner does the beaver discover the delicious odour than he sits upright, sniffs about in every direction, and squeals with excitement until he can get up to it.  The trapper, knowing this, always carries a supply of castor, or bark-stone; and when he reaches a stream or any other water near which he believes beavers may be found, he sets his trap, about six inches under the water.  He then chews the end of a twig, dips it in the castor, and sticks it in with the scented end uppermost, just a little above the water.  The nearest beaver, on discovering the scent, hurries up to the spot; and, if a young animal, is nearly certain to be caught by the trap.  The older beavers are more knowing and cautious, and frequently bite off the end of the twig without entangling themselves.