Mean temperature of the body deduced from ob servations four times re peated upon each of eight 58 (100 F.) men, under the torrid zone, the external tempe rature varying from 26° to 30° c. (79°, F.) Mean temperature of the same eight men observed three times in the tern- 11 (99° F.) perate zone, the external temperature varying from to to 62° These results confirm those of Dr. Davy by so much the more as they were made within the same limits of external temperature. The mean rise of the temperature of the body un der the influence of that of the air is also equally confirmed ; but the amount is still less than as given by the English observer.
It seems impossible, then, to doubt that the natural variations in the temperature of the air affect that of the body of man ; but this is only in a very trifling degree, at least within the limits of temperature in which any extant ob servations have been made. It is greatly to be regretted that neither of the observers qunted had opportunities of ascertaining the effects of much lower temperatures than those they have given. There are, it is true, many isolated ob servations made by voyagers in the Arctic regions, both upon animals and man, and although conducted in no regular series, or as points of comparison with one another, they still lead to the same general result, namely, that great differences in the tempera ture of the air cause slight differences in the temperature of the body of animals. Thus, in the voyage of Captain Parry it was observed that the temperature of the Mammalia was very high. NVith the external thermometer at — 4 (— F.), the temperature of the white hare was 3 F.). NVith the thermometer at — 32°, 8 F.), the tempe rature of a wolf was 4- 5 (105 F.); the temperature of the Arctic fox, under nearly the same circumstances, namely, when the thermo meter was standing at — 35° (-31° F.), was as high as 41° 5 (107° F.). Similar obser vations have since been made in the same high latitudes upon man.
The variations in the temperature of warm blooded animals according to that of the seasons has been studied by the present writer, who con firms the results just stated. The experiments of the writer were made upon a great num ber of sparrows recently taken at different seasons of the year, which is preferable to keeping these creatures in captivity for any length of time. The mean temperature of these birds rose progressively from the depth of winter to the height of summer, within the limits of from two to three degrees centigrade. The:observations made on sparrows exhibited the greatest differences. In the month of Feb ruary the mean temperature of these birds was found to be 8 (105° F.) ; in April F.), in July 43°, 77 (111° F.). The
temperature from this time began to decline, and followed, in the same ratio in which it had increased, the sinking temperature of the year.
Influtnce of media upon temperature.—The media in which animals live do not act solely in the ratio of their temperature, but also by virtue of the intensity of their cooling or heating power. Thus air and water at the same degree of heat will have a very different influ ence on the temperature of the bodies plunged in them. The power of air in heating or cooling is commonly known to be very inferior to that of water. Bodies acquire or lose tem perature much more slowly in air than in water. A water-bath according to its temperature com municates sensations of heat or cold far more rapidly and powerfully than an air-bath. The writer and M. (lentil made the following experiment :—A young man seventeen years of age, of strong constitution and in good health, after remaining for twenty minutes in a bath the water of which marked 13° It. (6t°, 5 F.), whilst the air was R. (63° F.), half an hour afterwards was found to have lost half a degree of his original heat in the mouth and hands, and a degree anda half in the feet. This temperature of the air may be regarded as a mean, or intermediate between heat and cold, and may be termed temperate (6 to 62° F.). It was superior to that of the water by a degree It., and yet the water of thebath, after immersion in it for 110 longer a time than twenty minutes, bad reduced the temperature of the body according to its parts from half a degree to a degree and a half It.
.Uccts of external temperature upon an isolated part of the body.—Under this head let us examine, 1st, the extent of the effect, and 2nd, its influence on other parts. The facts we shall borrow from the researches just quoted, those namely of myself and M. Gentil. The hand, at 29° R. (98° F.) having been kept immersed in a tub of water cooled down to ± 4° It. (41°F.), in all during twenty minutes, five minutes after it had been taken out of the water, marked no higher a tempera ture than 10° It. (55° F.) This experiment shows how rapid and extensive, and how much beyond what could have been anticipated, may he the refrigerating effects of cold water applied to an extremity. Another not less remarkable result is the singular slowness with which the temperature of an extremity is regained, although exposed to the gentle warmth of the air. The hand in the above experiment, after the lapse of twenty-five minutes from the time it was removed from the water, was still no higher than 16i° It. (69° F.), and after the expiration of an hour and a half it was only 24eR. (87° F.). The foot, in the same cir cumstances, gave nearly analogous results.