If the fat bear could see itself previous to hybernation in November, and again be introduced to its own photograph upon awakening from its sleep in March, it would be prepared to swear against its own identity. It arises from its winter's nap in wretched condition, having lived entirely upon capital instead of income. Young shoots, and leaves of spring, wild tubers which it scratches from the ground, detected by its keen sense of smell, together with snails, beetles, worms, and everything that creeps upon the earth, now form the bill of fare, until the summer brings forth the welcome fruits that reproduce the condition which the bear had lost through hybernation. It is impossible to unravel many of the mysteries of Nature, and the cause which prompts the instinct of a winter's sleep will always remain doubtful. I should myself attribute hybernation to the necessity of repose at a period when food was impossible to procure. The body can exist for an incredible length of time, provided that it is capable of undisturbed rest, which appears in a certain degree to take the place of extraneous nutriment. It is well known that every exertion of the muscles is a loss of power, the force of the body being represented by heat. To lift a weight or to move a limb requires a certain expenditure of heat, which means force; this loss of heat and power is recuperated by food; thus in the absence of provisions for the necessary supply, there would be no loss of heat if there is no exertion. Sleep is the resource, as the body is not only at rest, but the brain is also tranquil; there is accordingly a minimum of exhaustion. Human beings have been known to live without food of any kind (excepting water) for a period of forty days, and have then resumed their ordinary course, simply confining themselves to moderate diet for the first few days after their long abstinence. In a time of starvation in Africa I have frequently composed myself to sleep in the absence of my daily food, and I have awoke without any disagreeable craving for a meal. Continued sleep will to a certain extent render the body independent of other nutriment, and I should imagine that the custom of hybernation has been induced by necessity. At a season when the fruits of the earth are exhausted, the ground frozen to a degree that would render scratching for roots impossible, an animal that was dependent upon such productions for its existence must either starve or sleep. The sleep is in itself a first stage of the process of starvation. The creature that can sleep through an existence of four months without food, and lose the whole of its fat during that interval of inaction, has already lost all that supported life during the period of total abstinence--the fat, or carbon. If it were to begin another turn of sleep in its exhausted state, it would be unable to support its existence.