680 



ANIMAL HEAT. 



gradually lose it, as has been shown in a 

 former passage of this article. The native of 

 the colder clime is more robust, and his nervous 

 system, less impressible, resists painful sensa- 

 tions in a greater degree, and is not over- 

 whelmed by the first effects of noxious influ- 

 ences. This conclusion is also susceptible of 

 demonstration by the way of direct experiment. 

 If during summer a frog be completely im- 

 mersed in a small quantity of water at the ordi- 

 nary temperature of this season of the year, 

 and the same experiment be repeated during 

 winter with water heated to the summer pitch, 

 the animal will live much longer in the latter 

 than in the former instance. The nervous sys- 

 tem of the animal, by the continued action of 

 the cold of the autumn and winter, has been 

 rendered much more capable of resisting noxi- 

 ous influences, as we have had occasion to see 

 already. It is on the same principle that the 

 I 1 inlander, according to the account of Acerbi, 

 can endure a bath at a much higher tempera- 

 ture than it could be borne by a native of a 

 warm or more temperate climate. 



EFFECTS OF VARIOUS OTHER CAUSES OF MODI- 

 FICATION IN EXTEllNAL 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. Intheclimate of northern France 01 Eng- 

 land it would be impossible to stand a vapour- 

 bath at a temperature between 40 and 50 c. 

 (104 to 122 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. M. Delaroche found that he could 

 not remain in a vapour-bath raised in the 

 course of eight minutes from 37.5 to 51,25c. 

 (100 to 125 .) for more than ten minutes 

 and a half, although the tath fell one degree. 

 M. Herger 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 53 ,7fic. (106to 129F.). 

 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 98, 88 c. 

 (210 F.), within a degree or two, conse- 

 quently, of the ordinary boiling temperature 

 of water. His 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 109,48 c. ; and Sir Charles 

 Blagden went still further, having exposed his 

 body during eight minutes to the contact of 

 dry air heated up to the extraordinary pitch 

 of 115,55 and 127,7c. (240 and 260 F.). 

 In assigning 40 or 50 c. (104 or 122 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 lo 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 70 and even 75 c. 

 (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 coois 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 fact 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 olher 

 morbid conditions. According to the state of 



