A Treatise on Anatomy, Physiology, and Hygiene (Revised Edition) by Calvin Cutter (read more books .txt) 📕

545. The true sources of animal heat, or calorification, are still imperfectly known. No hypothesis has, as yet, received the concurrent assent of physiologists. We see certain phenomena, but the ultimate causes are hidden from our view. Its regular production, to a certain degree, is essential both to animal and vegetable life.

546. There is a tendency between bodies of different temperature to an equilibrium of heat. Thus, if we touch or approach a hot body, the heat, or caloric passes from that body to our organs of feeling, and gives the sensation of heat. On the contrary, when we touch a cold body, the heat passes from the hand to that body, and causes a sensation of cold.

547. The greater number of animals appear cold when we touch them; and, indeed, the temperature of their bodies is not much above that of the atmosphere, and changes with it. In man, and other animals that approach him in their organization, it is otherwise. They have the faculty of producing a sufficient quantity of caloric to maintain their temperatures nearly at the same degree, under all atmospheric changes, and keep themselves warm.

548. Those animals whose proper heat is not very perceivable, are called cold-blooded; as most species of fishes, toads, snakes, turtles, and reptiles generally. Those animals 253 which produce sufficient heat independently of the atmosphere surrounding them, are called warm-blooded; as man, birds, quadrupeds, &c.

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 254 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?

553. In order to render it certain that there was no fallacy, says Sir Charles Blagden, “in the degree of heat shown by the thermometer, but that the air breathed was capable of producing all the well-known effects of such a heat on inanimate matter, I put some eggs and beefsteak upon a tin frame placed near the thermometer, and farther distant from the cockle than from the wall of the room. In about twenty minutes the eggs were taken out, roasted quite hard; and in forty-seven minutes, the steak was not only dressed, but almost dry.”

554. If a thermometer be placed under the tongue of a healthy person, in all climates and seasons the temperature will be found nearly the same. Sir Charles Blagden, “while in the heated room, breathed on a thermometer, and the mercury sank several degrees; and when he expired forcibly, the air felt cool as it passed through the nostrils, though it was scorching hot when it entered them in inspiration.”

Observation. Did not the human body possess within itself the power of generating and removing heat, so as to maintain nearly an equality of temperature, the most fatal consequences would ensue. In northern latitudes, especially, in severe weather of winter, the blood would be converted into a solid 255 mass, and on the other hand, the fatty secretion, when subjected to equatorial heat, would become fluid, and life would be extinguished.

What is related of Chantrey? Of Chaubert? Of Sir Charles Blagden? 553. Give Sir Charles’s own statement. 554. What is said of the temperature of the human tongue? Mention the experiment by Sir Charles Blagden. What would be the effect if the human system did not maintain an equality of temperature?

555. To enable man, and other warm-blooded animals, to maintain this equilibrium of temperature under such extremes of heat and cold, naturally suggests two inquiries: 1st. By what organs is animal heat generated? 2d. By what means is its uniformity maintained?

556. The ancients had no well-arranged theory on the subject of animal heat. They believed that the chief object of respiration was to cool the blood, and that the heart was the great furnace where all the heat was generated. At a later period, Mayow, from his discoveries respecting respiration, asserted that the object of respiration was to produce heat, and denied that the blood was cooled in the lungs.

557. When it was discovered that, both in combustion and respiration, carbonic acid was produced and oxygen absorbed, it led Dr. Black to conclude that breathing was a kind of combustion by which all the heat of the body was produced. This theory was objected to, because, if all the heat was generated in the lungs, like those parts of a stove in contact with the fuel, they would be at a higher temperature than those parts at a distance, which was known not to exist.

558. The next theory, and one which received the sanction of the scientific men of Europe, was proposed by Dr. Crawford. He agreed with Dr. Black that heat not only was generated in the lungs, but that the arterial blood had a greater capacity for heat than the venous, and that this increase of capacity takes place in the lungs. At the moment heat is generated, a portion of it, under the name of latent heat, is absorbed and conveyed to the different parts of the body 256 Wherever arterial blood is converted into venous, this latent heat is given out. But, unfortunately for this theory, Dr. Davy proved the capacity of both, for heat, to be nearly the same.

555. What inquiries are naturally suggested? 556. What was the theory of the ancients? What did Mayow assert at a later period? 557. What was the