EFFECTS OF vAnrous OTHER CAUSES OF FICATION IN EXTERNAL AGENTS.
The effects of external heat and cold on the sensations and on the system in general are not altogether dependent on degrees of temperature. Even at the same degree atmospheric effects are often very different, being principally influ enced by the state of dryness or moisture, and by that of motion or rest, of the air. Speaking generally, media exert modifying influences other than those comprised in their tempera ture upon the phenomena of animal heat. Eva poration is a powerful cause of cooling, which increases in the same measure as the evapora tion. In the summer season, consequently, during a state of the weather in which the temperature is the same, but the hygrome tric condition different, the heat of the body will be higher in moist than in dry air. In the same way we observe all the effects of excessive temperature upon the body to be much more intense with a moist than with a dry atmo sphere. In the climate of northern France orEng land it would be impossible to stand a vapour bath at a temperature between 40° and c. to F.) for more than ten or twelve minutes ; but with a perfectly dry state of the air it is possible to bear a temperature twice, or more than twice as high during the same space of time. N. Delaroche found that he could not remain in a vapour-bath raised in the course of eight minutes from to to F.) for more than ten minutes and a half, although the bath fell one degree. M. Berger was compelled to make his escape within twelve minutes and a half from a vapour bath the temperature of which had risen ra pidly from 41°,25 to to 120°F.). Both of these experimenters felt themselves become weak and unstable on their legs, and were affected with vertigo, thirst, &c. The weakness and thirst continued through the remainder of the day. But in the course of Dr. Dobson's experiments, a young man con tinued for twenty minutes in a dry-air stove, the temperature of which was c. F.), within a degree or two, conse quently, of the ordinary boiling temperature of water. llis pulse, which usually beat 75 times in a minute, now beat 164 times. This, however, is by no means the degree of heat that can be and that has been en dured. M. Berger for five minutes bore a temperature of and Sir Charles Blagdeu went still further, having exposed his body during eight minutes to the contact of dry air heated up to the extraordinary pitch of and c. and F.). In assigning or c. or F.)
for the limits of moist temperature that can be borne by the inhabitants of these coun tries, we are perfectly aware that in other lati tudes it can be greatly exceeded. Thus Acerbi, in his journey to the North Cape, informs us that the Finnish peasantry remain for half an hour or more in a vapour-bath, the temperature of which finally rises to and even 75° e. (158° and 167° F.). We have already given the reason of this difference of constitution.
Experimental philosophers have not yet tried the precise comparative cooling effects of dry air and of watery vapour ; but all are agreed that the powers of the moist atmosphere are by far the most considerable. To measure the comparative effects upon the economy the• fol lowing experiments were instituted. In equal spaces, the one filled with air at the point of extreme humidity, the other with extremely dry air, were placed young birds of the same age, which were as yet incapable of maintaining their temperature at its proper height when taken out of the nest. It was found that they lost temperature nearly in the same propor tion in the same space of time when the air was either at the point of extreme humidity or of great dryness. Therefore moist air tends to cool at least as much as dry air by evapora tion. It cools both by the abstraction of heat and by its action on the nervous system. Its action on the nervous system is of a debilitating nature, and therefore tends to diminish the power of generating heat. The sensation of cold was evidently greater in the moist air, as was shown by the shivering of the animal. There can be no doubt that the action of vapour in this case is complicated by a physi cal influence in the one instance, and by a pecu liar physiological effect on the nervous system in the other ; for it is well ascertained that water, as contrasted with air, has a debilitating effect upon the economy. General experience comes in support of these results; men have ever agreed that moist and cold states of the atmo sphere and humid and cold climates were more difficult to be borne than those of an opposite character. Such climes in filet are in them selves extremely insalubrious. By their pecu liar effects on the economy they tend greatly to lessen the power of producing heat, and they also engender intermittent fevers, among other morbid conditions. According to the state of the economy and the degree of the external temperature, watery vapour tends to refrigerate still more in winter, and to add to the heat in summer.