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/lit25760/689/
ANIMAL HEAT. 
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. 
The state of the atmosphere in regard to 
motion or rest modifies to a great extent the 
effects of a given temperature upon the body. 
Refrigeration by simple contact increases in 
amount with the rate of motion of the air. The 
same law holds good in regard to evaporation, 
and indeed this process always complicates the 
results proceeding from simple contact. The 
cause of refrigeration in this case is consequently 
double. It is easy, therefore, to imagine how 
powerful a cause of cooling a cold wind must 
be. But observation can alone give any ade¬ 
quate idea of the extent of its influence in this 
respect. Mr. Fisher, one of the surgeons in 
the expedition under the command of Sir 
Edward Parry to the Polar Seas, has given us 
an account of its extraordinary effects. In the 
frozen regions around the arctic circle, the 
hardy voyagers under Capt. Sir E. Parry found 
that they could stand a cold adequate to freeze 
mercury when the air was perfectly calm, much 
more easily than a temperature nearly 50° F. 
higher when it blew. The air in motion in 
this case, therefore, produced a sensation of 
cold that was equal to such a depression of 
temperature as is indicated by a fall of 50° of 
the scale of F.—a most prodigious difference. 
Sudden transitions of temperature also exert 
a great influence independently of any limits ; 
in the first place, because the intenseness of 
the sensation of cold or of heat is in propor¬ 
tion to the suddenness of the abstraction, or of 
the communication of heat ; and again, be¬ 
cause the faculty of adaptation to different 
degrees of external temperature is not acquired 
all at once, but is only attained in a certain 
lapse of time, and by gradual modifications 
in the constitution. We therefore see that 
those countries of which the temperature is 
very high in the day, but very low in the night, 
are subject to diseases that seem to belong 
more peculiarly to cold and moist latitudes, 
or to marshy lands where malaria prevails. 
But the transition from hot to cold is not 
limited to the suddenness of the thermal de¬ 
pression ; it extends to the refrigeration by the 
action of the wind. This is another among 
the many reasons why in the latitudes of Eng¬ 
land, France, &e. spring is a more dangerous 
season than autumn. There are, however, cer¬ 
tain cases of sudden transition that are useful 
and salutary, as for instance,when the heat of the 
body is excessive, and is doing mischief, whe¬ 
ther it be induced by an elevated external 
temperature, or proceeds from the violent and 
involuntary action of our organs. Then re¬ 
frigeration even of the most sudden kind, pro¬ 
vided it be restrained within proper limits, 
becomes beneficial. It is thus that the 
affusion of cold water produces such excellent 
effects in cases of extreme excitement, and 
where the temperature is really above the 
natural standard. This process is even to be 
regarded as one of the most brilliant tri¬ 
umphs of modern medicine. It is much to 
681 
be regretted that recourse is not had to it more 
frequently. It is evident that the proper time 
for the use of this powerful means is that in 
which congestion has not yet passed into ob¬ 
stinate engorgement, that is to say, in the 
beginning of the disease, in which by allaying 
excitement congestion is diminished. The 
favourable moment for using the cold affusion is 
that in which the skin is hot and dry, which 
is also the period of the highest excitation. 
The experiments upon the effects of baths, 
quoted above, tend also to show the propriety of 
the practice ; in citing these, we mentioned that 
the diminution of temperature produced in the 
body lasted for hours, and that the reaction 
consequent upon the use of the bath did not 
carry the temperature higher than the pitch it 
possessed at starting. It is obvious that the 
effects of the cold affusion are to be derived 
from the principles previously established ; 
since we have referred the production of heat 
to two general conditions of the economy, 
one of which is the state of the nervous sys¬ 
tem. Now the affusion of cold water acts 
directly upon this system. There is another 
powerful method of tempering animal heat, 
which flows from the other general condition, 
upon which the production of heat depends, 
viz. the state of the blood. We have seen 
above that the respective proportions of the 
serous mass of the blood and of its red glo¬ 
bules exert an important influence; that in 
the class of vertebrate animals which produce 
smaller quantities of heat, the proportion of 
the serum was in the inverse ratio of the 
faculty of calorification. Whence it follows, 
that in cases of excessive heat of body, to 
reduce the quantity of red globules would 
prove an effectual mode of reducing the tem¬ 
perature. Now this is precisely what is done 
by bloodletting. The effect, however, in this 
way is not instantaneous. The first influence 
of bloodletting is simply to lessen the quan¬ 
tity of the blood, and this is the extent to 
which ideas of the influence of the abstraction 
of blood are generally confined. There is, 
however, a consecutive influence, which is at 
the least as important, and which proves much 
more lasting. As the person who has been let 
blood confines himself at the same time to 
low diet, and principally to liquids, it is obvious 
that the blood is recruited in its quantity 
principally by additions of watery particles, 
without any notable or even sensible addition 
of globules. The blood is therefore altered 
essentially in its constitution ; the proportion 
of its component fluid and solid elements is 
changed, and this in direct proportion to the 
extent and frequency of the venesections. The 
consequence of this is a diminution of tempe¬ 
rature, unless other causes oppose such an ef¬ 
fect. 
Bloodletting, it must be observed, is not the 
sole means of accomplishing such a change in 
the constitution of the blood. We can pro¬ 
duce a similar effect by exciting one or all of 
the secretions which are thrown off by the 
body. Secretion is performed at the cost of 
the blood, which supplies both of its elements
        

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