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of hair, and, relatively to its weight, a greater production of heat, than a
horse. Further, as remarked by Bergmann, the smaller animals need a
relatively greater supply of food.

The large animals living in the tropics, such as the elephant and
hippopotamus, are often remarkable for the small amount of hair upon the
body and for their love of bathing, whereby the loss of heat is favoured.
The largest mammals, the whales, are able by means of their enormous
size and special layers of fat to resist the cold of the Arctic seas, and
maintain a temperature equal to that of mammals living in the tropics.
Water-fowl, especially those which inhabit cold regions, are noted for
the protection afforded against cold by their down and feathers.

These indications from the natural history of animals are fully con-
firmed by experimental observations. The determinations made by
Letellier,^ and by Eegnault and Eeiset,- show that the intake of oxygen
and the output of carbon dioxide are relatively greater in small than in
large animals ^ ; starvation is more rapidly fatal to small than to large
animals,'* for during life they consume a relatively larger quantity of
proteid.^ Further, Eubner ^ has determined the heat production of dogs
of different size, and finds that the smaller animals produce relatively
more heat in proportion to their weight than the larger animals, and that
the heat production is proportional to the surface of the body. The
following table gives some of these results : —



Weight.


Surface.


Surface per Kilo.
Weight.


Heat Production per
Kilo, per Day.

Air=15°.


Heat Production per

Square Metre of

Surface.


Kilo.
31-2

18-2

9-6

6-5

3-19


Sq. Cm.
10,750

7662

5286

3724

2423


Sq. Cm.
344

421

550

573

726


Kilo-cal.
35-68

46-20

65-16

66-07

88-07


Kilo-cal.
1036

1097

1183

1153

1212



Similar results have been obtained by Langlois ^ in the case of
children.

1 Ann. de chim. etphys., Paris, 86r. 3, tome xiii. p. 478.

- Ibid., 1849, tome xxvi. p. 299 ; 1863, tome Ixix. p. 129.

^ See article "Chemistry of Respiration," this Text-hook, vol. i. pp. 706-8,

^ Chossat, "Recherches expi^rimentales sur I'inanition," Paris, 1843.

^ Voit, Hermann's "Handbuch," Ed. vi. S. 88.

^ Ztschr.f. Biol., Munchen, 1883, Bd. xix. S. 535.

"^ Centralbl. f. Physiol., Leipzig u. Wien, 1887, S. 237-



854 ANIMAL HEAT.

Eubner calculates that the tissues of a rat produce five and one-
third times, the tissues of a sparrow thirteen times, as much heat as the
same weight of tissue in a man.



The Influence of the Nervous System upon the
Eegulation of Tempeeatuee.

The nervous system exercises a control on both of the factors
concerned in the regulation of temperature ; upon the loss of heat
by means of the vasomotor system, which regulates the amount of
blood in the deep and superficial parts of the body, and by the respira-
tory centre which controls the frequency and depth of respiration ; upon
the production of heat through the nerves which control the activity
of the tissues, chiefly the muscles. The control is of the nature of
a reflex, and the sensory nerves of the skin and muscles are probably
the most usual lines of the afferent impulses. The most important
nervous centres are the vasomotor and the respiratory, but in addition
to these and the so-called " motor " centres some physiologists maintain
that special " heat centres " exist in the brain.

Vasomotor control of temperature. — -The blood distributed to the
body comes from the heart, where the temperature is, with the excep-
tion of the liver and a few other internal parts, the highest in the body ;
this warm blood is carried to the extremities and the surface of the
body, where the temperature is lower. Now, three zones may, as
Eosenthal ^ has pointed out, be recognised — an internal warm zone, an
intermediate temperate zone, and an external cool zone ; the first is
represented by the deep organs and tissues, the second by the more
superficial parts, and the third by the skin and subcutaneous tissue.
Under ordinary circumstances the temperature will decrease from
within outwards, for the most important seats of chemical change and
heat production are situated within the first two zones, and the loss of
heat is greatest from the surface of the skin. The blood circulating in
the vessels distributes the warm blood of the interior to the superficial
parts, and carries back cooler blood from the surface to the interior.
The difference, therefore, in temperature between the interior and the
surface will depend upon the rapidity and the quantity of the blood
circulating through the different zones of the body ; this distribution is
regulated by the central nervous system through the vaso-constrictor
and vaso-dilator nerves. The vasomotor nerves have their centre in
the medulla oblongata, and probably subordinate ones in the spinal cord ;
the distribution, however, of these centres and nerves is discussed else-
where ; here they will be considered merely as part of the nervous
mechanism which regulates temperature.

When the cutaneous and subcutaneous vessels are constricted, the
quantity of blood distributed to the skin is diminished, the difference
between the temperature of the surface of the body and its surroundings
is less, and consequently less heat is lost. This condition is brought
about by external cold, and thus the heat of the body is economised and
its normal temperature is maintained, or may, under certain circum-
stances, be raised, for it has already been shown that the first effect of a
cold bath is to raise the temperature in the axilla and rectum. On the
other hand, exposure to warmth causes a dilatation of the cutaneous
^ Hermann's "Handbuch," 1882, Bd. iv. Th. 2, S. 381.



VASOMOTOR CONTROL OF TEMPERATURE. 855

vessels, the difference between the temperature of the skin and its
surroundings is increased, and likewise the loss of heat. Thus the first
effect of a warm bath may be a fall in the temperature of the internal
parts. The loss of heat by this flushing of the skin with hot blood and
by sweating may be very great, as shown by the rapid fall in tempera-
ture during the sweating state of ague or the crisis of pneumonia.

These changes in the calibre of the vessels can be brought about
reflexly, not only by sensations of heat and cold but by those of pain ;
further, emotions can effect these changes, as in the blushing of excite-
ment or shame, and the pallor of fright or anger ; in fact, emotions may
in different individuals have opposite effects upon the vascularity of the
skin.

An impression conveyed by the sensory nerves of one part of the
body can influence the calibre of the vessels, not only on the same side
but also on the opposite side. Thus, Brown-Sequard and Tholozan,^ found
that plunging one hand in warm water raised the temperature of the
opposite hand also. Waller,'^ however, has failed to confirm this.

The explanation of the part played by the vasomotor nerves in
the regulation of temperature is not so simple as may appear from a
first consideration, for the problem is complicated by the fact that
an increase or decrease in the vascularity of the skin is accom-
panied by a similar change in the production of sweat ; further, it is
possible that the alterations in vascularity may affect the metabolism
of the tissues. Upon this latter point there has been considerable dis-
cussion. The first and most important experiment in this connection
is that of Bernard,^ who found that section of the cervical sympathetic
caused a dilatation of the blood vessels and a rise of temperature in the
ear of the same side. The enlargement of the blood vessels results in a
greater and more rapid flow of blood through the ear, and this would
naturally raise the temperature of the part. Bernard, however, did not
look upon this explanation as complete ; he held that the nervous
system regulated not only the circulation but also the production of
heat in the tissues, for he states, among other arguments, that section of
the cervical sympathetic, after previous ligature of the veins of the ear,
still caused a rise of temperature. According to Bernard, the nerve was
both vaso-constrictor and frigorific. It was to be expected, however,
that this view would be contested, for although a certain amount of
heat would be produced in the ear, as in the metabolism of all tissues,
yet that amount would be small, for the cartilage and other tissues of
the ear are not the seats of an active exchange of material.

Numerous experimenters * have decided against Bernard's theory, and
have attributed the changes in the temperature of the ear to alterations

■^ Journ. de Tanat. etphysiol. etc., Paris, 1858, tome i. p. 497.

" Note communicated to the Avriter.

" "Lemons sur la physiologie et la pathologie du systeme nerveux," 1858, tome ii,
p. 490 ; "Lecons sur la clialeur animale," 1876, p. 297.

■* Brown-S(5quard, Med. Exam., Philadelphia, 1852, p. 489, and 1853, p. 9 ; Budge,
Compt. rend. Acad. d. sc, Paris, tome xxvi. p. 337; Ztschr. v. d. Vcrein f. Heilk. in
Freussen, 1853, Bd. xxii. S. 149 ; Waller, Compt. rend. Acad. d. sc, Paris, 1854,
tome xxxvi. p. 378; De Ruyter, "De actione atropaj belladonnte," Diss., 1853 ; Schiff,
" Untersuch. z. Physiol, des Nervensystems," 1855, Bd. i. S. 124 ; AUg. Wien. med. Ztg.,
1859, S. 318 ; Kussmaul and Tenner, Untersucli. z. Naturl. d. Mensch. u. d. Thiere,
1855, Bd. i. S. 92 ; Callenfels, Ztschr. f. rat. Med., 1858, Bd. vii. S. 157 ; Jacobson and
Landre, Nederl. Tijdschr. v. Geneesk., Amsterdam, Bd. i. Heft 3 ; Donders, Wunderlicli's
"Medical Thermometry," p. 148; Bayliss and Hill, Journ. Physiol., Cambridge and London,
1894, vol. xvi. p. 351.



856 ANIMAL HEAT.

in the blood supply alone. The difference in the temperature of the
two ears, after section of the cervical sympathetic on one side, may be
even as great as 12° or 16°, but it is proportionate to the difference in
the quantity of blood (Schiff). If the two subclavians and the carotid
on the same side as the divided sympathetic are ligatured, the tempera-
ture of the ear falls below the normal, owing to the want of collateral
circulation ; on the other hand, the temperature of the ear can be raised
by ligature of the subclavians without section of the sympathetic nerve ;
this is due to the increased pressure of blood in the carotid artery
(Kussmaul and Tenner). The ears of a rabbit are to be looked upon as
part of the mechanism for regulating temperature by the varying
quantity of blood exposed ; section of one sympathetic causes a fall in
the temperature of the ear of the opposite side (Jacobson and Landre).

In addition to the vasomotor nerves of the skin, it is important to
remember that the vasomotor nerves to the respiratory tract and lungs
may play an important but subordinate part in the regulation of the
loss of heat.^ The importance of this method of regulation without doubt
varies in different animals, and is greater in those with a thick coat of
fur, as in the dog, who, when he is too hot, pants with open mouth and
lolling tongue. This rapid respiration, 150-200 per minute in heated
dogs, has been specially studied by Ackermann,^ Goldstein,^ and Eiegel ; ^
more recently, Eichet ^ has shown that a dog gives off from its respiratory
tract, every hour, about 1 grm. of water for every kilo, of its body
weight, when the external temperature is moderate, but when exposed
to a hot sun it discharges ten times as much moisture and increases its
respirations from 28 to 230 per minute. Any cause which prevents a
dog from breathing rapidly and freely, such as a tight muzzle, causes a
rise of two or three degrees in the animal's temperature.

The temperature of the body after damage or section of the
spinal cord. — An examination of the numerous observations made upon
the influence of injury or section of the spinal cord shows at first sight
much confusion and apparent contradiction in the results. In the
majority of cases, however, the results can be harmonised by taking into
account the numerous factors of secondary import. In the first place,
the experiments are only strictly comparable when they are performed
upon similar animals under similar conditions. Thus the effect will vary
according to the level of the injury or section of the spinal cord ; a
section high up in the cord will involve a more extensive paralysis than
one low down, and the more extensive the paralysis the smaller the
production, and the greater the loss of heat, owing to the dilated cutane-
ous vessels. A section above the splanchnic area will obviously have a
greater effect than one below that area ; a section high up in the cord
will interfere with the movements of respiration, whereas one low down
will have comparatively little effect. Again, an animal with only the
lower extremities and part of the trunk paralysed, may be able to main-
tain its temperature by greater variations in the production and loss of
heat in the parts still under control. The size of the animal is import-
ant, for the bigger the animal the smaller is its surface in relation to its

^Bradford and Dean, Journ. Physiol., Cambridge and London, 1894, vol. xvi. p. 34.
Here an account of previous work on the subject will be found.
^ Dautsches Arch,, f. klin. Med., Leipzig, Bd. ii. S. 361.

^ Inaug. Abhandlung, Verhandl. d. 'phvs.-med. Gesellsch. in Wurzhicrg, 1871, S. 156.
^ Firchoiv's Archiv, 1874, Bd. Ixi. S. 396.
■' Compt. rend. Soc. de bioL, Paris, 1887, p. 482.



NER VO US CONTR OL OF TEMPERA TURE. 85 7

mass, and thus the loss of heat due to vasomotor paralysis is less serious
than in a small animal. Animals also differ in their method of
regulation ; some, as in the case of man, have a well-developed vaso-
motor system for the cutaneous surface, which is so slightly protected by
natural covering ; others, as in the case of dogs, have a thick fur, and
regulate their temperature chiefly by variations in the production of
heat and in the loss of heat from the respiratory tract. The distribu-
tion and part played by the sweat glands varies greatly, as shown by a
comparison of men and horses with dogs and cats. It is to be noticed
further, in this respect, that marked differences exist even in individuals
of the same race and variety ; thus, some men and horses sweat much
more readily and profusely than others.

In addition to the above factors, it is necessary to consider the
external conditions under which the injured animal finds itself. The
external temperature greatly modifies the part played by the loss of heat
from the paralysed parts. Most animals adopt a different posture,
according to their need of heat or cold ; thus a heated dog, rabbit, or
mouse lies with extended trunk and limbs, whereas the same animal
when it is cold, coils or huddles itself together. It is almost imneces-
sary to point out that a paralysed animal could not assume these
instinctive postures. A normal rabbit tied down in an extended position
loses an abnormal quantity of heat, and its temperature falls, and in
some cases the body is so greatly cooled that death results.^

The above facts must therefore be borne in mind during any ex-
amination of the effects of section or injury of the spinal cord.

Attention was first drawn to the influence of the nervous system upon
temperature, by the experiments and clinical observations of Benjamin
Brodie.'^ He found that, after the head of an animal was cut off, or the
cord divided high up in the cervical region, the circulation of the blood
still continued when artificial respiration was performed, but the tem-
perature fell even more quickly than in a dead animal. This Brodie
correctly attributed to the great loss of heat from the circulating blood, for
if the circulation was stopped by ligature of the heart, the fall of tem-
perature was much retarded. It was also found that woorara (curari) and
essential oil of almonds, by suspending the action of the central nervous
system, also caused a fall in temperature. Brodie further compared the
discharge of carbon dioxide by normal rabbits with that of rabbits with
the brain removed or poisoned by woorara or the essential oil of almonds ;
he states that the same quantity of carbon dioxide is formed in each of
these cases, and therefore that the heat production is not due to chemical
change but to nervous action. This conclusion is not warranted by the
results of the determinations of the respiratory exchange, and the
results themselves are not comparable, for, even when it was possible, the
experiments were not made upon the same animals.

The work of Brodie led to numerous experiments and discussions on
this subject by Chossat,^ Hale,* Legallois," Wilson Philip,^ Hastings,'^

^ Legallois, Ann. de chim. et ijliys., Paris, 1817, Ser. 2, tome iv. p. 21.

2 PhiL Trans., London, 1811, vol. ci. p. 36 ; 1812, vol. cii. p. 378 ; Med.-Chir. Trans.,
London, 1837, voL xx. p. 146.

^ Deutsches Arch. f. d. Physiol., Halle, 1822, Bd. vii. S. 282.

■* London Med. and Phys. Journ., vol. xxii.

^ Ann. de chim. et phys., Paris, 1817, S^r. 2, tome iv.

^ "Experimental Inquiry into the LaAVs of the Vital Functions," London, 1818, 2nd
edition, p. 197 et seq.

"^ Quart. Jourii. Sc. Lit. and Arts, London, 1823, vol. xiv. p. 96.



858 ANIMAL HEAT.

and C. J. B. Williams.^ The results on some points confirmed, on others
contradicted, Brodie's conclusions. Wilson Philip found that artificial
respiration caused a fall in the temperature of intact animals, and that a
slow ventilation prevented the temperature of the brainless animal
from falling as quickly as that of a dead animal. Hastings obtained
similar results, and Williams confirmed the observations of Wilson
Philip, that the temperature of a brainless animal might even be slightly
raised by artificial respiration. Legallois carried out a very complete
series of experiments upon the subject, and came to the following con-
clusions : that a brainless animal upon which artificial respiration was
performed suffered a reduction of temperature, but it was from one to
three degrees less than in a dead animal ; that in cooling through a
certain number of degrees it parted with more heat than a dead animal ;
that inflation of the lungs of normal animals lowered their temperature,^
and if the ventilation were continued for a long time they might die of
cold ; and, finally, that a fall in temperature might be produced by any
condition which constrained or impeded the respiration.

Tscheschichin ^ found that section of the spinal cord between the
third and fourth cervical vertebrae caused the temperature of a rabbit to
fall from 38°-9 to 32°-l. This he attributed to the increased loss of heat
from the paralysed cutaneous vessels, and to diminished production of
heat ; the higher the section, the more extensive the paralysis of the blood
vessels, and the greater the loss of heat ; stimulation of the peripheral
end of the cord caused contraction of the blood vessels, and the loss of
heat was less.

In rabbits, section of the spinal cord at the commencement of the
dorsal region caused the rectal temperature to fall from 40° to 24° in
five hours (Bernard).^ In guinea-pigs, section of the upper dorsal region
produced a progressive fall in the rectal temperature from 38°-9 to 16°
in twenty-four hours, when the animal died (Pochoy).^

Fischer^ found a rise of 0°'5 to 1°"7 in the temperature of dogs and
rabbits after complete section of the cervical portion of the spinal cord,
but no rise when the operation was performed in the dorsal or lumbar
regions. He concluded that an inhibitory centre for heat existed in
the cervical region of the cord. A series of experiments were made by
Naunyn and Quincke'^ upon the effect of crushing the spinal cord.
They selected dogs of large size, and with thick fur, in order to diminish
the importance of the loss of heat. They foimd that, after the cord was
crushed at the level of the sixth cervical vertebra, the rectal tempera-
ture fell, unless the excessive loss of heat due to vasomotor paralysis was
prevented by a fairly high external temperature ; if the air was warm, the
temperature rose two or three degrees, and even higher after death.
These observers concluded that there were nerve fibres which, passing
from the brain to the spinal cord, inhibited the production of heat * ; and
that, after section, the production as well as the loss of heat were

^ " Observations on the Changes produced in the Blood in the course of its Circulation,"
London, 1835.

^ See also Fawcett and Hale White, Jourii. Physiol., Cambridge and London, 1897,
vol. xxi. p. 435.

" Arch. f. Anat., Physiol, u. ivissensch. Med., 1866, S. 151.

•* "Lecons sur la chaleur auiraale," 1876, p. 161.

'^ These, Paris, 1870.

'' CentralM. f. d. mad. Wissensch., Berlin, 1869, No. 17.

"• Arch. f. Anat., Physiol, u. wissensch. Med., 1869, S. 174, 52L

** See also Ott and CoUmar, .Joitrn. Nerv. and Mcnt. Bis., N.Y., 1887, p. 428.



NERVOUS CONTROL OF TEMPERATURE.



859



increased, and if the augmentation of the latter was not excessive, the
temperature of the body rose. On the other hand, Eiegel ^ found that
the production of heat was diminished, and he explains the rise of
temperature in Naunyn and Quincke's cases as due to absence of the
rapid breathing whereby normal dogs regulate their temperature.
Further, Schroff- found a rise in the temperature of dogs when they
were kept in a warm chamber after opening of the spinal canal, without
damage to the spinal cord.

Eosenthal ^ repeated IsTaunyn and Quincke's experiments, but never
found any rise of temperature, unless the animals were kept in a
chamber warmed to 32°. If the section was made lower down in the
cord, more muscles remained under the control of the animal, and by
the contraction of these muscles more heat was produced, and the
temperature raised when the external air was warm. Eosenthal further
points out that it is probable that septic fever was the cause of the rise
of temperature in some of Naunyn and Quincke's dogs.

Pflliger's "^ experiments upon the respiratory exchange of rabbits, after
section of the spinal cord in the lower cervical region, show that such
an animal is comparable to a cold-blooded animal; a rise in external
temperature increases, a fall diminishes, the metabolism and the
temperature of the animal. The same result is even more markedly
shown in the case of a smaller animal. Thus the following figures
show the effect of sudden changes in the external temperature upon the
output of carbon dioxide of a mouse before and after section of the spinal
cord in the lower cervical region : ^ —



Before Section of Cord. Consecutive
Periods of 15 Minutes.


Three Hours after Section of Cord. Con-
secutive Periods of 15 Minutes.


CO, in
Decimilli-
grammes.


Tempera-
ture of
Water Bath.


Remarks.


COjin
Decimilli-
grammes.


Tempera-
ture of
Water Bath.


Remarks.


391
372
558
572


25° -0
24°'0
12°-5
12°-5


Mouse very quiet.
Mouse active.


222
229
250
158


22° -0
22° -0
ll°-75
ll°-75


Mouse quiet.

Mouse moves its fore-
limbs very actively.
Mouse quiet.



We may conclude, therefore, that in animals the general effect of
section of the spinal cord in the lower cervical region is a fall in the
temperature of the body, due to a reduction in the metabolism of the
paralysed muscles, and to excessive loss of heat consequent upon the
vasomotor paralysis. The exceptional cases appear to be due to a high
external temperature, and to interference with the rate of respiration,
which in dogs plays an important part in the cooling of the body.

1 Arcli.f. d. ges. PMjsioL, Bonn, 1872, Bd. v. S. 629.

^ Sitzungsh. d. k. Akad. d. Wissensch. Math.-naturw. Gl., Wien, Bd. Ixxiii. Abth. 3,
S. 141.

^ "Zur Kenntniss d. Warraeregulierung bei den warmbliitigen Thieren," S. 35 ; Hermann's
"Handbuch," Bd. iv. Th. 2, S. 4-37.

^ Arch.f. d. ges. Physiol., Bonn, 1878, Bd. xviii. S. 321.

5 Pembrey, " Proc. Physiol. Soc," Journ. Physiol., Cambridge and London, 1894-
1895, vol. xvii.



86o



ANIMAL HEAT.



An examination of the cases of crushed spinal cord in man shows
discordant results, in some cases a marked rise, in others a fall in the
temperature of the body. The following table gives the chief data in
some of the cases recorded : —



Sex and
Age.


Seat of Injury.


Temperature.


Remarks.


Observer.


M.


Crush at level


43°-9 (111° F.), be-


Diaphragmatic breath-


Brodie.i




Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 119 of 147)