545-570. _What is said respecting animal heat?_ 545. Are the true sources of animal heat known? What do we see? 546. What is the tendency between bodies of different temperatures? Give an explanation. 547. What is said of the temperature of animals? 548. What is meant by cold-blooded animals? By warm-blooded animals? -=-=-=-=-=-=-=-=-=-=-=-= 549. The temperature of man is about 98°, (Fahrenheit's thermometer,) and that of some other animals is higher; the temperature of birds, for example, is about 110°. It is obvious, that in most parts of the globe, the heat of the atmosphere is, even in summer, less than that of the human body. In our latitude, the mercury rarely attains 98°, and sometimes it descends to several degrees below zero. 550. Captain Parry, with his ship's company, in his voyage of discovery to the arctic regions, wintered in a climate where the mercury was at 40°, and sometimes at 55° below zero. Captain Back found it 70° below zero. These were 72° and 102° below the freezing point, or about 200° below that of their own bodies, and still they were able to resist this low temperature, and escape being "frost-bitten." 551. Captain Lyon, who accompanied Captain Parry in his second voyage to the northern regions, found the temperature of an arctic fox to be 106°, while that of the atmosphere was 32° below zero; making a difference between the temperature of the fox and that of the atmosphere, of 138°. Captain Scoresby found the temperature of a whale, in the Arctic Ocean, to be 104°, or nearly as high as that of other animals of the same kind in the region of the equator, while the temperature of the ice was as low as 32°, and the water was nearly as cold. These facts show what a strong counteracting energy there is in animals against the effects of cold. 552. On the other hand, it has been ascertained by numerous and well-conducted experiments, that the human body can be exposed, even for a length of time, to a very high temperature, without essentially elevating that of the body. Chantrey, the sculptor, often entered the furnace, heated for drying his moulds, when the temperature indicated by the thermometer was 330°. Chaubert, the Fire-King, is said to have entered ovens when heated to 600°. In 1774, Sir Charles Blagden entered a room in which the mercury rose to 260°. He remained eight minutes without suffering. -=-=-=-=-=-=-=-=-=-=-=-= 549. What is the temperature of the human body? Of birds? How does the heat of the atmosphere in summer, in our latitude, compare with that of the human system? 550. What is related of Captain Parry? Of Captain Back? 551. Of Captain Lyon? Of Captain Scoresby? What do these facts show? 552. What has been ascertained on the other hand? -=-=-=-=-=-=-=-=-=-=-=-=