Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25760/688/
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 
Finlander, 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 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 hygromé¬ 
trie 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 theclimate of northern France orEng- 
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°,25 c. 
(100° to 125° 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 53°,75c. (106°to 129°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 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°,7 c. (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 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 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 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 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 other 
morbid conditions. According to the state of
        

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