The male beaver carries in two bladders the _castoreum officinale_, a very powerfully-scented, oily fluid, which the hunter collects in a bottle and mixes with spirits, partly to keep it from putrefying, but principally to impart to it another odour, by which the beaver is induced to believe that it emanates from a stranger. In this bottle the hunter thrusts a twig, the point of which he moistens with its contents, then thrusts the other end of it into the bank of the beaver pond, so that the point projects over the water at a spot where it is not very deep. Exactly under this twig he places in the water his heavy iron trap, to which he fastens, by a long thong, a very large bush, which he throws on the bank. So soon as a beaver raises its nose on the surface of the pond, it smells the castoreum on the twig, swims up to convince itself whether it emanates from a stranger, and while going on land steps on the trap, which closes and catches its forefeet. It darts away with the trap into deep water, and wrestles furiously with the torturing iron, for which reason a beaver thus captured is never found to have sound teeth--till, quite exhausted, it tries to rise to the surface to breathe. The trap, however, keeps it down, and the prisoner is drowned in its own element. The next morning the hunter sees the bush floating over the spot where the beaver is lying, and pulls it up with the trap. The beaver hunters who visit these western deserts often take some dozens of traps with them, so that when they arrive at a colony, it is speedily destroyed, on which occasion they also capture in the same way the otters living there.