Such are the effects on animals of the elevation of temperature. Let us now see what becomes of them when immersed in cold media. Some curious facts with respect to the freezing of certain animals have long been known. During his voyage to Iceland, in 1828 or 1829, Gaimard, having exposed in the open air a box filled with earth in which toads were put, opening it after a certain time, found the reptiles frozen, hard and brittle; but they could be restored to life when put in warm water. Many ancient authors cite similar cases, and we can almost bring ourselves to understand how a great English physiologist might for a moment have given them the whimsical interpretation that he did. John Hunter fancied it might be possible to prolong life indefinitely by placing a man in a very cold climate, and there subjecting him to periodical freezing. The man, he said, would perhaps live a thousand years, if, at the end of every ten years, he were frozen for a hundred, then thawed out at the end of the term for ten years more, and so continuously. "Like all inventors," Hunter adds, "I expected to make my fortune by this scheme, but an experiment completely undeceived me." Putting carp into a freezing mixture, he observed, in fact, that, after being entirely frozen, they were dead, past recovery. The case is the same with all other animals, as the late and very remarkable experiments of F. A. Pouchet have proved.
The influence of cold on organized beings varies, according as we regard superior animals or the inferior species. In general, it may be said that it requires a very low surrounding temperature to chill many animals, because the vital heat they develop resists the process with energy. Yet the mammals of arctic regions, in spite of their thick coat of fur, can only brave the temperature of the pole (sometimes equal to 40° (cent.) below zero, the freezing point of mercury) by living under the snow where they make their lair. The Esquimaux, too, dig huts in it, where they pass their wretched days. When the organism can neither react nor protect itself against temperatures so low, death by freezing quickly overtakes it. The body is stiffened, and retains afterward a state of remarkable incorruptibility. Every one knows the story of the antediluvian mammoths, discovered in the polar ice, where they had been buried, as fresh as animals just dead. While heat destroys the tissues, cold preserves them.
Through what mechanical means does cold become mortal? It seems to act on the nervous system. Travellers relate that in polar regions an unconquerable disposition to sleep overcomes men attacked by very low temperatures. On the icy shores of Terra del Fuego, Solander said to his companions, "Whoever sits down falls asleep, and whoever falls asleep never wakes again." This inclination is so overpowering that many of his attendants gave up to it, and he himself sank down for a moment on the snow. It is said that, during the winter of 1700, two thousand soldiers of Charles XII.'s army perished in the sleep to which they surrendered, under the influ-
