CALORIFICATION, OR ANIMAL TEMPERATURE. The function, we have now to consider, is one of the most important to organic existence, and one of the most curious in its causes and results. It has, consequently, been an object of interesting examination with the physiologist, both in animals and plants, and as it has been presumed by a large class of speculatists, to be greatly owing to respiration, it has been a favourite topic with the chymist also. Most of the hypotheses devised for its explanation have, indeed, been of a chymical character; and hence it will be advisable to premise a few observations regarding the physical relations of caloric or the matter of heat,—an imponderable body, according to common belief, which is generally distributed throughout nature. It is this, which constitutes the temperature of bodies, by which is meant, the sensation of heat or cold which we experience, when bodies are touched by us; or the height at which the mercury is raised or depressed by them, in the instrument called the thermometer;—the elevation of the mercury being caused by the caloric entering between its particles, and thus adding to its bulk; and the depression being produced by the abstraction of caloric. Caloric exists in bodies in two states;—in the free, uncombined or sensible, and in the latent or combined. In the former case, it is intimately united with the other constituent elements of bodies, and is neither indicated by the feeling nor by the thermometer. It has, consequently, no agency in the temperature of bodies; but, by its proportion to the force of cohesion, it determines their condition; whether they shall be solid, liquid or gaseous. In the latter case, caloric is simply interposed between the molecules, and is incessantly disengaged, or abstracted from surrounding bodies; and, by impressing the surface of the body or by acting upon the thermometer, it indicates to us their temperature. Equal weights of the same body, at the same temperature, contain the same quantities of caloric; but equal weights of different bodies, at the same temperature, have by no means the same quantities. The quantity, which one body contains, compared with that in another is called its specific caloric, or specific heat; and the power or property, which enables bodies to retain different quantities of caloric, is called capacity for caloric. If a pound of water, heated to 156°, be mixed with a pound of quicksilver at 40°, the resulting temperature is 152°,—instead of 98°, the exact mean. The water, consequently, must have lost four degrees of temperature, and the quicksilver gained 112°; from which we de duce, that the quantity of caloric, capable of raising one pound of mercury from 40° to 152° is the same as that required to raise one pound of water from 152° to 156°; or, in other words, that the same quantity of heat, which raises the temperature of a pound of water four degrees, raises the same weight of mercury one hundred and twelve degrees. Accordingly, it is said, that the capacity of water for heat is to that of mercury, as 28 to 1; and that the specific heat is twenty-eight times greater. All bodies are capable of giving and taking free caloric, and, consequently, all have a temperature. If the quantity given off be great, the temperature of the body is elevated. If it take heat from the thermometer, it is cooler than the instrument. In inorganic bodies the disengagement of caloric is induced by various causes; such as electricity, friction, percussion, compression, the change of condition from a fluid to a solid state; and by various chymical changes, giving rise to new compounds, so that the caloric, which was previously latent, becomes free. If, for example, two substances, each containing a certain amount of specific heat, unite, so as to form a compound whose specific heat is less, a portion of caloric must be set free, and this will be indicated by a rise in the temperature. It is this principle which is chiefly concerned in some of the theories of calorification that have been proposed. The subject of the equilibrium and conduction of caloric has already been treated of, under the sense of touch; where several other topics are discussed, that bear more or less upon the present inquiry. It is there stated, that inorganic bodies speedily attain the same temperature, either by radiation or conduction; so that the different objects, in an apartment, will exhibit the same degree of heat by the thermometer. The temperature of animals, however, being a vital operation they retain the degree of heat peculiar to them, with but little modification from external temperature. There is a difference, however, in this respect, sufficient to cause the partition of animals into two great divisions—the warmblooded and the cold-blooded; the former comprising those animals, whose temperature is high, and but little influenced by that of external objects; the latter those whose temperature is greatly modified by external influences. The range of the temperature of the warm-blooded—amongst which arc all the higher animals—is limited; but of the cold-blooded extensive. The following Table exhibits the peculiar temperature of various animals in round numbers;—that of man being 98° or 100°. According to the table, it will be observed, that the inhabitants of the Arctic regions, whether belonging to the class of mammalia or birds, are amongst those whose temperature is highest. That of the Arctic fox is, indeed, probably higher than the amount given in the table, being taken after death, when the temperature of the air was as low as 14° of Fahrenheit, and when loss of heat may be supposed to have taken place rapidly. - The temperature of the smaller insects it is, of course, impracticable to indicate; but we can arrive at an approximation in those that congregate in masses, as the bee and the ant; for it is impossible to suppose with Maraldi, that the augmented temperature is dependent upon the motion and friction of the wings and bodies of the busy multitudes. Juch found that, when the temperature of the atmosphere was -18° of Fahrenheit, that of a hive of bees was 44°; and, in an ant-hill, the thermometer stood at 68° or 70°, when the temperature of the air was 55°; and at 75°, when that of the air was 66°. The power of preserving their temperature within certain limits is not, however, possessed exclusively by animals. The heat of a tree, examined by Mr. Hunter, was found to be always several degrees higher than that of the atmosphere, when the temperature of the air was below 56° of Fahrenheit; but it was always several degrees below it when the weather was warmer. Some plants develope a considerable degree of heat, during the pe riod of blooming. This was first noticed by Lamarck in the Arum italicum. In the Arum cordifolium of the Isle of Bourbon, HuBERT found, when the temperature of the air was 80°, that of the spathe or sheath as high as 134°; and Bory De St. Vincent observed a similar elevation, although to a less degree, in the Arum esculentum, esculent arum or Indian kale. The animal body is so far influenced by external heat, as to rise or fall with it; but the range, as we have already remarked, is limited in the warm-blooded animal; more extensive in the coldblooded. Dr. Currie found the temperature of a man, plunged into sea-water at 44°, sink in the course of a minute and a half after immersion, from 98° to 87°; and, in other experiments, it descended as low as 85°, and even as 83°. It was always found, however, that, in a few minutes, the heat approached its previous elevation; and, in no instance, could it be depressed lower than 83°, or 15°. below the temperature at the commencement of the operation. Similar experiments have been performed on other warm-blooded animals. Hunter found the temperature of a common mouse to be 99°, when that of the atmosphere was 60°; but when the same animal was exposed for an hour to an atmosphere of 15°, its heat had sunk to 83°; but the depression could be carried no farther. He found, also, that a dormouse, whose heat in an atmosphere at 64° was 81°, when put into air, at 20°, had its temperature raised, in the course of half an hour, to 93°; an hour after, the air being at 30°, it was still 93°; another hour after, the air being at 19°, the heat of the pelvis was as low as 83°,—an experiment, which strongly proves the great counteracting influence exerted, when animals are exposed to an unusually low temperature. In this experiment, the dormouse had maintained its temperature about 70° higher than that of the surrounding medium, and for the space of two hours and a half. In the hybernating torpid quadrupeds the reduction of temperature, during their torpidity, is considerable. Jenner found the temperature of a hedge-hog, in the cavity of the abdomen, towards the pelvis, to be 95°, and that of the diaphragm 97° of FAHRENHEIT, in summer, when the thermometer in the shade stood at 78°; whilst in winter, the temperature of the air being 44°, and the animal torpid, the heat in the pelvis was 45°, and of the diaphragm 4840. When the temperature of the atmosphere was at 26°, the heat of the animal, in the cavity of the abdomen, where an incision was made, was reduced as low as 30°; but, what singularly exhibits the power possessed by the system of regulating its temperature, when the same animal was exposed to the cold atmosphere of 26°, for two days, its heat, in the rectum, was raised to 93°, or 67° above that of the atmosphere. At this time, however, it was lively and active, and the bed, on which it lay, felt warm. In the cold-blooded animal, we have equal evidence of the generation of heat. Hunter found, that the heat of a viper, placed in |