I was awakened from sleep by an unusual sound. Now, anyone sleeping in a new place grows accustomed to the sounds of the night in that region, and, once accustomed to them, accepts them in sleep; but any new sound is apt to obtrude. Just as a city-dweller spending several nights on a farm may accustom himself to the noises of chickens, birds, the wind, frogs, may be awakened by the new note of a toad trilling because it is strange to the chorus to which he has become accustomed, so I was aware of a new sound in the chorus of whippoorwills, owls, and nocturnal insects which invaded the night.