Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/1181/
TOUCH. 1171 
physical qualities, concerning which we re¬ 
ceive information through the sense of touch. 
Sense of Temperature. — This sense is 
called into action when there is a difference 
between the temperature of the sensory organ 
and that of the surrounding medium, or of 
substances with which it is specially brought 
into contact. It is one of which the intensity 
is determined, more perhaps than that of any 
other sensation, rather by the relative than by 
the absolute condition of the body which 
excites it. Thus, if one hand be immersed 
for a time in hot water, and the other in cold, 
and both then be plunged into tepid water, 
this will seem cool to the former and warm to 
the latter. So, again, a person coming out of 
cold air into an atmosphere of moderate tem¬ 
perature, derives from it the feeling of genial 
warmth, whilst another, coming into the very 
same atmosphere from one much hotter, com¬ 
plains of its chillness. Again, when the tem¬ 
perature of different substances is compared 
by the hand, the sense is not so much influ¬ 
enced by the absolute amount of caloric 
possessed by each, as by their power of 
imparting cold or heat to the sensory organ. 
Hence substances which are good conductors 
(such as metals or marble) are felt to be 
colder than those which conduct heat badly 
(such as wood), although really of the same 
temperature, because they draw off the heat 
of the sensory surface more rapidly ; whilst, 
on the other hand, if both be warmer than 
the sensory surface, the best conductors will 
seem to be the hottest, because their caloric 
is most readily imparted. Further, the sense 
of temperature is influenced in a remarkable 
degree by the extent of surface on which the 
impression is made. Every one is familiar 
with the fact that hot water in which a single 
finger may be held without inconvenience, 
will be felt intolerably scalding when the 
whole hand is immersed in it. And it has 
been shown by Professor Weber, that if one 
vessel of water be heated to 98° and another 
to KH0, and the whole of the hand be im¬ 
mersed in the former, while the finger alone 
is immersed in the latter, a wrong judgment 
of their relative temperatures will be probably 
given, that which is really the cooler being 
pronounced the hotter, on account of the 
larger extent of surface on which it acts. 
This mistake was made in soqie of his experi¬ 
ments, when the difference was as much as 
eight degrees ; the cooler water being at 98°, 
and the hotter at 106°, and yet the former 
being esteemed the hotter. So, again, the 
immersion of the entire hand enables minute 
differences of temperature to be detected, 
which could not be recognised by the immer¬ 
sion of a single finger. By the former method, 
a difference of only one-third of a degree may 
be distinguished ; the entire hand being im¬ 
mersed, repeatedly and successively, in two 
vessels of water, differing only that much in 
their relative warmth. But it is remarked by 
Professor Weber, that these minute differ¬ 
ences are best detected when the medium 
examined does not fall short of, or exceed 
very considerably, the usual temperature of 
the body ; just as the ear can best perceive a 
difference of tone in sounds which are neither 
very acute or very grave.* 
It is a remarkable fact, discovered by Pro¬ 
fessor Weber, that the left hand is in most 
persons more sensible to variations of tem¬ 
perature than the right. Thus, when the 
hands of a person lying in bed, and haying 
exactly thq same temperature, are plunged 
each in a separate vessel of hot water, the 
left hand is believed to be in the hotter 
medium, although the water in which it is 
immersed is really one or two degrees colder 
than the other. This difference is the more 
remarkable, as the power of tactile discrimina¬ 
tion is usually greater in the right hand ; and 
it is attributed by Professor Weber to a 
difference in the thickness of the epidermis, 
the left hand usually having a thinner epi¬ 
dermis than the right, especially in the palm, 
because it is less used. But this will only 
apply to the hand ; and since (as will be 
presently shown) we possess a greater power 
of discriminating pressures through the entire 
surface of the left side than through that 
of the right, it would seem much more pro¬ 
bable that there is an original difference in 
the tactile endowments of the two sides 
respectively. There is certainly a strongly 
marked difference between different parts of 
the trunk in regard to their sensibility to tem¬ 
perature, as is experienced by those who 
sponge themselves over with cold water im¬ 
mediately on leaving their bed in the morning. 
In the writer’s case, the parts most sensitive 
to the cold are in the centre of the dorsal 
region behind; in front, between the lower 
end of the sternum and the umbilicus ; and 
the corresponding portions of the flanks. 
These spots are among the parts of the in¬ 
tegument least possessed of tactile discrimi¬ 
nation ; and yet the cold sponge passing over 
them seems to be much lower in temperature 
than when it is applied to other parts. 
Some further experiments have recently 
been made by Professor Weber, to determine 
whether the sense of temperature is received 
through any other channel than the sensory 
apparatus contained in the integuments.f 
The fii^t means of which he availed himself 
for deciding this question, was that afforded by 
the results of accident or surgical operations, 
in which a portion of skin has been left defi¬ 
cient. Thus, in three cases in which a large 
portion of the skin had been destroyed by a 
burn, and in which healing had not advanced 
so far as to renew the organ of touch, it was 
found that no correct discrimination could be 
made between two spatulas, one of them at a 
temperature of from 48° to 54°, the other of 
from 113° to 122°, which were brought into 
* He further remarks, that the comparison be¬ 
tween two temperatures can be best made when the 
impressions are not simultaneously made upon two 
different parts, but are made in quick succession upon 
the same part ; as mentioned hereafter to be the case 
in regard to weights. 
f Müller’s Archiv. 1849. Heft, iv. s. 273—283. 
4 F 2
        

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