The brown and polar bears have the same habit of lying up for the winter. An Esquimau informed Captain Lyon that in the first of the winter the pregnant bears are always fat and solitary. When a heavy fall of snow sets in the animal seeks some hollow place in which she can lie down, and remains quiet while the snow covers her. Sometimes she will wait until a quantity of snow has fallen and then digs herself a cave; at all events it seems necessary that she should be covered up by the snow. She now goes to sleep and does not wake until the spring sun is pretty high, when she brings forth two cubs. The cave by this time has become much larger by the effect of the animal's warmth and breath, so that the cubs have room enough to move, and they acquire considerable strength by continually sucking. The dam at length becomes so thin and weak that it is with great difficulty she extricates herself, which she does when the sun is powerful enough to throw a strong glare through the snow which roofs the den. Then the family comes out, and will take anything that comes along in the way of food. During the long sleep the temperature of the bear's blood is reduced to almost that of the surrounding air. The power of will over the muscles seems to be suspended, respiration is hardly noticeable, and most of the vital functions are at a complete standstill--the entire body sleeping, as it were. The male grizzly bear never hibernates. The young and the females, however, build nests, one of which measured ten feet high, five feet long, and six feet wide. Bats are great winter sleepers, and in most of the known caves they can be found during the cold months clinging to the walls and to each other. During hibernation their respiration ceases almost entirely, and only the most careful use of a stethoscope can reveal it. The air that has surrounded numbers of them has been carefully examined and not the slightest evidence found of its having been breathed; and, stranger yet, they can exist in this condition in gas, that, were they awake, would prove instantly fatal. A machine has been invented to examine these and other animals while in this condition. A delicate index records the slightest pulsation, while a thermometer shows the rise and fall of the temperature at every moment during the period; and by an arrangement of the wing, the circulation of the blood is recorded. A more delicate experiment can hardly be imagined, as a strong breath, a sneeze, or a footfall will cause the subject of the experiment to recover enough to respire several times; and the effect of this on the machine can be imagined when it is known that though, while in this condition, they produce no effect upon the oxygen of the air about them, they consume when respiring more than four cubic inches of oxygen an hour.