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than the left, because its walls lie nearer to the liver and other
abdominal organs, which have a high temperature, while the left
ventricle is surrounded by lung. It was found, in fact, that the
difference in temperature could be reduced to a minus quantity by
artificially lowering the temperature of the abdominal cavity. Bernard
does not accept this explanation as satisfactory ; for he points out that
in Hering's observation the right ventricle was half a degree warmer
than the left, although the heart, owing to a congenital defect, was
outside the thorax.

The temperature of the skin. — The temperature of the human skin
shows differences in different parts of the body, and is also subject to
variations due to alterations in the external temperature, the amount of
natural or artificial covering, the vascularity of the parts, and the
amount of evaporation taking place from the surface. Apart from
these variations, there is a difficulty in measuring accurately the
temperature of the skin ; a mercurial thermometer applied to the skin
receives heat from the surface in contact with the skin, and loses
heat from the surface exposed to the air. If, on the other hand,
the thermometer is covered with a non-conductor, or the external
temperature is raised, then the heat of the part of the skin observed
is increased. To overcome these difficulties, thermo-electric methods
have been used.^

The disadvantages of these thermo-electric methods are the complexity

1 Arch.f. d. ges. Physiol., Bonn, 1871, Bd. iv. S. 558.

- See "Chemistry of Respiration," tliis Text-book, vol. 1. p. 754.

^ Christiani and Kronecker, Arch. f. Physiol., Leipzig, 1878, S. 334; Kunkel, Ztschr. f.
Biol., Miinchen, 1889, Bd. xxv. S. 55 ; Masje, Virchow's Archiv, Bd. cvii. S. 17, 267;
Geigel, Verhandl. d. phys.-med. Gesellsch. in Wiirzhurg, 1888, N. F., Bd. xxii. S. 8 ;
Stewart, Stud. Physiol. Lab. Owens Coll., Manchester, 1891, vol. i. p. 100.



830



ANIMAL HEAT.



of the apparatus required, the necessity of graduation, and the time
taken in observation. Bayliss and Hill ^ found that the wire-resistance
thermometer ^ could not be employed for the investigation of changes
of temperature in a warm-blooded animal ; the slightest movements, as
those of artificial respiration, in the curarised animal producing deflec-
tions of the galvanometer. A Hat mercurial thermometer, on the other
hand, is easily applied, and furnishes comparative data of considerable
value.^

Some of the earliest experiments with mercm'ial thermometers were
made by J. Davy, who obtained the following results, when the
temperature of the room was 21° : —



Sole of the foot .


32^^-2


Middle of the rectus femoris


32°-78


Between internal malleolus




Groin


35°-84


and tendo Achillis .


33^-89


One inch below navel .


35"-00


Middle of tibia .


33°-06


Left sixth rib over heart


34°-44


Middle of calf .


33°-89


Right sixth rib .


33°-89


Bend of the knee


35°-00


Axilla (closed)


36°-67


Middle of the thigh .


34°-44







Kunkel * used a thermo-electric method, which was exact to about
0°"1, and obtained the following results for the temperature of different
parts of the skin of a healthy muscular man, 35 years of age, 179 cm.
in height, and 84 kilos, in weight. The temperature of the room
was 20^ : —



Forehead . . . 34° "l-
Over malar bone .
Cheek under malar bone
Lobe of ear ....
Back of hand . . 32° •5-

Palm of hand (closed for some



34'
34^



4-



-34°-4
34°-l
34°-4
28°-8

-33°-2

-35°-l
34°-8
33°-l
33°-7

34°-0



Arm ....


34°-3


Sternum


34°-4


Over pecto rails major .


34°-7


Over heart .


34°-6


Right iliac fossa .


34° -4


Left „


34°-6


Back, over sacrum


34°-2


,, over ribs ,


34°-5


Buttock


32°-05


Thigh.


34°-2


Calf ....


33°-6



time)
Palm of hand (open)
Wrist .
Forearm

„ upper part

Experiments were also made upon the effect of exposure to cold.
Thus, after the man lightly clothed had taken a walk for half an hour
in a cold, sharp, north-east wind (-5°), the following temperatures were
observed — face, 27°-7-28°-7 ; back of hand, 24°-7 ; chest and abdomen,
32°-l ; arm, 30°-7-31°-l ; but after he had remained for forty minutes in
a room at 15°, the face had a temperature of 34°-6, the back of the hand
31°'2, and the abdomen 33°-9.

Working the muscles of one arm raised the temperature of the skin

1 Joiirn. Plujslol., Cambridge and London, 1894, vol. xvi. p. 352.

2 RoUeston, ibid., 1890, vol. xi. p. 208.

■'Davy, Phil. Trans., London, 1814, vol. civ. p. 590; " Rcsearclies," London, 1839,
vol. i. p. 150; Alvarenga, "Precis de thermom(5trie clinique g^nerale," 1871, p. 45;
Waller, " Proc. Physiol. Soc," Journ. Physiol., Cambridge and London, 1894, vol. xv. ;
Hale White, Croonian Lectures, Lancet, London, June 19th, 1897, Brit. Med. Journ.,
London, 1897, vol. i. p. 1654; Pembrey, "Proc. Physiol. Soc," Journ. Phi/siol., Cam-
bridge and London, 1897, vol. xxi.

* Ztschr.f. Biol., Miinchen, 1889, Bd. xxv. S. 55.

•'"' This low reading Kunkel attributes to the loss of heat by conduction when the man
was sitting down.



RE G ULA TION OF TEMPERA TURE. ^^ i

of that part above 34'^, whereas the temperature of the abdomen was
only 32° -5. The highest temperature observed in healthy men was
35°"6, on the skin of the face.

Kunkel concludes from his observations that the temi^erature of the
human skin is almost constant, and that the temperature of the body is
regulated to a very slight degree by changes in the temperature of the
skin.

The Kegulation of Tempeeature.

Inasmuch as the constancy of temperature varies in different
animals, and even in the same animal under different conditions, such
as age and hibernation, so also various grades of perfection are observed
in the power of regulation. In man this power is so greatly developed
that his temperature is almost the same, whether he lives in the Arctic
regions, with an external temperature 50° below zero, or in the Tropics,
where the temperature of the air may be as high as 48°. For shorter
periods a man can remain in a room heated to 121° without the
temperature of his body rising above the normal.^ Other mammals
have a less perfect regulation, as shown by the greater variations of
their temperature.

In young immature mammals and birds the power of regulation
is imperfect, for when they are exposed to cold their temperature falls,
and they pass into a condition in which they resemble the cold-blooded
animals, their temperature rising and falling with that of their sur-
roundings. A similar imperfection in regulation is seen in some
mammals during hibernation. Lastly, in the so-called cold-blooded
animals, there are various grades in this capacity for regulating tempera-
ture, as is shown by the high temperature of bees in winter, when com-
pared with that of most of the lower animals, in which there is a mere
trace of regulation.

Even in those warm-blooded animals which possess a perfect power
of heat regulation, there are limits to this power. If the animal be
exposed to excessive cold, the loss of heat is great, and only within
certain limits can compensation be effected by an increased produc-
tion of heat. When compensation fails, then the animal's temperature
falls, its bodily and mental activities are diminished, and it passes into
a sleepy, unconscious condition which ends in death. Such a condition
is observed in men or animals before they are " frozen to death."

On the other hand, extreme heat can only be resisted within a
certain range ; the production of heat in the body can be diminished,
but not suspended ; the loss of heat can be greatly increased by sweating
and by a greater exposure of blood in the vessels of the skin, but if the
air be of a temperature equal to, or nearly equal to, that of the body,
and greatly laden with moisture, then the loss of heat is slight or even
suspended. Under such circumstances the internal temperature of the
animal rises rapidly to a point incompatible with life. The extremes
of heat and cold which can be borne without injury to life, have already
been discussed.

The mean temperature of the higher animals is fairly constant

under very great differences of external temperature, and to maintain

such a condition the loss and the production of heat must be almost equal.

That there is no perfect equality has already been shown in the daily

^ Bladgen, FMl. Trans., London, 1775, vol. Ixv. p. 484. Tliis article, p. 814.



832 ANIMAL HEAT.

variation of the temperature of the body, in the rise of temperature
observed after exercise, and during residence in tropical climates.

The regulation of temperature, therefore, embraces two processes —
regulation'^by varying loss of heat, regulation by varying production of

heat.

The regulation of heat production.— In considering the regulation
of heat production, it is necessary to trace out briefly the various
discoveries which have established, as a fact, that animal heat is due
to combustion within the tissues.

Historical account of facts and theories upon the sources of
animal heat.^ — The ancients considered animal heat to be beyond the reach
of physical and chemical laws. They could assign no cause for it, and there-
fore looked iipon it as some innate quality, something essentially "vital."
This " vital " heat was supposed to he concentrated in the heart (Plato, Aris-
totle, Galen), and to be distributed to the body by the blood in the veins. It
was prevented from accumulating by respiration, the chief function of which
was to cool and temper the blood.

As knowledge in physical and chemical processes increased, attempts were
made to give a rational explanation of animal heat. It was well known that
heat arose during fermentation, and by the contact of acid and base ; animal
heat was therefore considered to arise by some similar process or processes
taking place in the blood. Willis,^ about the year 1670, put forward the
theory that there is in the blood a combustion which depends upon the fer-
mentation excited by the combination of different chemical substances. Fric-
tion was another well-known source of heat, and was the explanation given by
Boerhaave ; ^ he considered that animal heat was due to the friction of the
blood corpuscles in the vessels. Stephen Hales -^ adopted this theory, and gave
certain experiments, which he thought supported it.

A much more correct opinion had already been formed in 1674 by Mayow,"'
who, after his experiments on the constitution of air and its relation to the
heat of combustion, extended the analogy of combustion to animal heat. He
held that the function of the lungs was not to cool the blood, but to enable
that fluid to absorb the nitro-aerial gas (oxygen) of the air, and so generate
heat.

Later research has shown that the heat of living things is not due to any
mystical so-called " vital " force, but to the processes of combustion, which
form one of the most important phenomena of life. The diff"erent steps by
which this knowledge has been attained are foimd in the discovery of Black, "^
that carbon dioxide was produced in animals by a process of combustion ; in
the work of Lavoisier '' and Crawf ord,^ who showed that the heat of an animal
micrht be accounted for by the processes of combustion ; in the researches of
Dulong 9 and Despretz,i° whose results, when critically examined and explained
by Liebig,^! formed an important support for the law of the conservation of
energy.

1 Accounts of the old theories will be found in C. Bostock, "Essay on Respiration"
"An Elementary System of Physiology," 2ud edition, 1828, vol. ii. p. 243 ; Gavarret
"Delachaleur produite par les etres vivants," Paris, 1855 ; and " Les phenomenes phy
sirmes de la vie," Paris, 1869; Lorain, "De la temperature du corps liumain," Paris,
1877, vol. i. p. 39 ; Rubner, Ztschr. f. Biol., Munchen, 1893-94, Bd. xxx. S. 73.

" "De Accensione Sanguinis." ^ " Aphor. cum Notis Sweiten," pp. 382, 675.

•* "Statical Essays," 2nd edition, 1733, vol. ii. p. 90.

■' "Tractatus Quinque," Oxonii, 1674.

" "Lectures on Chemistry," edited by Robi.son, Edinburgh, 1803.

"^ Hist. Acctd. roy. d. sc, Paris, 1777.

8 "De calore Animali," 1779; "Experiments and Observations on Animal Heat,"
1788.

"•* Ann. de chim. etphys., Paris, 1843, Ser. 3, tome i. p. 440.

10 Ibid., 1824, S^r. 2, tome xxvi. p. 337. '^ "Thierchemie," S. 28.



CHEMICAL CHANGE AND HEAT PRODUCTION 833

Helmholtz, Ludvvig, Pfliiger, and others, by their investigations upon the
production of heat in muscle, glands, and other tissues, and their determina-
tions of the respiratory exchange of animals, have indicated where and how
heat is produced. Finally, the exact determinations made by Eubner ^ upon
heat production and metabolism have proved that chemical change is the
cause of animal heat. Simidtaneous determinations of the exchange of
material and the production of heat in dogs, under different conditions as
regards diet, were made, and the results show that the heat of combustion of
the food, as determined in a calorimeter, is equal to the heat given off by the
animal ; in fact, the animal must be looked upon as a living calorimeter, in
which the food is burnt. The results are so exact that they prove the con-
servation of energy in a vital process.



Condition of the Animal.


Heat as Calculated.


Heat as found
by Calorimeter.


Percentage
Difference.


Fasting
Diet of fat .
Diet of flesh and fat
Diet of flesh


1296-3 cal.
1510-1 „

2492-4 ,,
4780-8 ,,


1305-2
1495-3

2488-0
4769-3


+ 0-69
-0-97
-0-17
-0-24



The above figures only give some of the results, but the mean of all the
experiments shows that the amount of heat, as determined directly by the
animal calorimeter, is only 0-47 per cent, less than the amount as calculated
from the heats of combustion of the different substances which have been
decomposed in the animal's body.

The Eelation of Chemical Change to Heat Production.

A consideration of the law of the conservation of energy leads to the
conclusion that the sole cause of animal heat is a chemical process, a
combustion of food substances by the oxygen taken in by the animal ;
as just mentioned, the experimental proof of this conclusion has been
recently given by Eubner. The chemical energy of the ingesta
manifests itself chiefly in two forms, heat and motion.

In this connection it is important to consider the heats of combus-
tion of the various substances which form part of an animal's body or
food, for it will thereby be possible to determine indirectly the amount
of heat produced by an animal. A given amount of chemical action is
accompanied by the production or the absorption of a definite quantity
of heat. The accurate determination of this quantitative relation is
beset with considerable difficulties, for the chemical changes in the
complex substances of animal tissues or food are rarely simple, and are
accompanied by physical changes, which have to be measured and taken
into account before the amount of heat due to the chemical change can
be estimated. Chemical decomposition is attended with the absorption
of a quantity of heat equal to that which would be evolved by the
combination of the same chemical substances.^ Therefore, in the



1 Ztsclir.f. Biol., Mlinchen, 1894, Bd. xxx. S. 135.

^ Favre and Silbermann, Ann. de cMm. et l^Tiys., Paris, 1842, Ser. 3, tome xxxiv.
p. 357 ; Woods, London, Edinburgh, and Dublin Phil. Mag., London, 1851, vol. ii. p. 268,
1852, voL iv. p. 370 ; Joule, ibid., 1852, vol. iii. p. 481.

VOL. I.— 53



834



ANIMAL HEAT.



estimation of the production of heat during a complex chemical change,
involving combination and decomposition, it is only necessary to
consider the first and final conditions of the substances, whatever may
have been the intermediate stages.^

The determination of the heat produced or absorbed by chemical
change is made by enclosing the acting substances in a chamber sur-
rounded by water or mercury, the rise or fall of temperature in which
indicates the amount of heat produced or absorbed, as the case may
be.2

The heat of combustion of substances of physiological interest has
been determined by various observers ; ^ the following table gives the
values of some of the most important substances : —



Substance,
1 gmi. (dry).


Heat of
Combustion.


Authoritj'.


Substance,
1 grni. (dry).


Heat of
Combustion.


Authority.


Hydrogen


33,881 cal.*


Andrews.


Casein .


5,855 cal.


Danilewsky.


)>


34,662 ,,


Favre and Sil-


,, . . .


5,867 ,,


Stohmann.






bermann.


,, ...


5,849 ,.


11


Carbon . .


7,900 ,,


Andrews.


Cows' milk .


5,733 „


Danilewsky.


„ Wood-


|8,080 ,, 1


Favre and Sil-


Women's milk


4,837 ,,


11


charcoal


bei'niann.


Fat ...


9,686 „




Cheese . . .


6,114 ,,


Frankland.


,, ...


9,423 ,,


Rubner.


Potatoes




3,752 ,,


) J


Dextrose .


3,939 ,,


Rechenberg.^


,,




4,234 ,,


Danilewsky.-'


Maltose .


4,163 ,,


,,


Lean beef




5,313 ,,


Frankland.


Milk sugar .


4,162 ,,


11


11




5,724 „


Danilewsky.


Starch . . .


4,479 ,,








5,641 .,


Stohmann.'^


,, ...


4,182 ,,


Stohmann.


,,




5,656 ,,


Rubner.'^


Cane-sugar .


4,176 ,,


Danilewsky.


White of egg


4,896 ,,


Frankland.


Glycogen . .


4,190 ,,


Stohmann.


Yolk of egg .


6.460 ,,




Cellulose .


4,185 ,,


,,


Butter . .


7,264 ,,


,,


Urea .


2,537 ,,


Danilewsky.


Bread crumb .


3,984 ,,


,,


,, ...


2,537 ,,


Stohmann.


Blood fibrin .


5,772 ,,


Danilewsky.


,, ...


2,525 ,,


Berthelot and


))


5,637 ,,


Stohniann.^






Petit. 10


Peptone . .


4,876 ,,


Danilewsky.


,, ...


2,523 .,


Rubner. ■*


j>


5,298 ,,


Stohmann.


Uric acid .


2,741 ,,


Stohmann.


Serum albumir


5,917 ,,


,,


Hippuric acid


5,678 ,,


))


Hfemoglobin .


5,885 „


"


Fseces .


4,479 ,,


Rechenberg.



The above table shows that the different foodstuffs have different
values as producers of heat, and from these it is possible to calculate
the physical value of one kind of food in terms of the others. The

1 Hess, quoted from Rubner [Ztschr. f. Biol., Mlinchen, 1894, Bd. xxx. S. 135).

^ For further details on such calorimeters, see Miller, "Chemical Physics," p. 338, and
Watts' "Dictionary of Chemistry," vol. iii. pp. 28, 103; Stohmann, Journ. f. prakt.
Chem., Leipzig (2), Bd. xix. S. 115 ; Bd. xxxix. S. 503.

2 Crawford, "On Animal Heat," 1788, 2ud edition, pp. 320, 333, 351 ; Favre and
Silbermann, Ann. de, chim. et'pliys., Paris, 1842, tome xxxiv. p. 357 ; Frankland, London,
Edinburgh, and Dublin Phil. Mag., London, 1866, vol. xxxii. p. 182 ; Hermann, Ber. d.
deutsch. chem. Ga^ellsch., Berlin, 1868, S. 18, 84; Rubner, Ztschr. f. Biol., Miinchen, 1885,
Bd. xxi. S. 357 ; Berthelot, Compt. rend. Acad. d. sc, Paris, 1886, tome cii. pp. 1211,
1284.

* Calorie = the heat required to raise 1 gi'm. of water 1" C. ; kilo-calorie = 1000 calories^
heat required to raise 1 kilo of water 1° C.

5 Arch./, d. gcs. PMjsiol., Bonn, 18S5, Bd. xxxvi. S. 230.
'^ Journ. f. prakt. Chem., Leipzig, Bd. xliv. S. 336.
' Ztschr. f. Biol., Miinchen, 1893-94, Bd. xxx. S. 88.
« Ibid., 1895, Bd. xxxi. S. 364.

'•* "Ueber die Veibrennungswarme organischer Substanzen," Leipzig. 1880.
^^ Compt. rend. Acad. d. sc, Paris, 1889, tome cix. p. 759.



CHEMICAL CHANGE AND HEAT PRODUCTION. 835



following table of isodynamic foodstuffs is taken from Danilewsky's
work : —





Fat.


Starch.


Grape-
Sugar.


Cane-
Sugar.


Cellulose.


Peptone.


Extract of
Meat.


100 grms.
casein =


61


133


1.51


142


133


121


135


100 grms.
fat


100


220


250


2-36


221


201


224


100 grms.
starch =


46


100


114


107


100


92


102



The above data are for physical values. It is necessary, therefore,
to determine how far the different foodstuffs undergo combustion in
the living body, and what values they have as producers of heat during
that combustion.

Kubner has shown that some of the products of the combustion of
proteid escape in the fseces as well as in the urine ; the heat value of
these substances must be determined and deducted from the heat of
combustion of proteid. The reduced or physiological heat value of
1 grm. of dry proteid is therefore only about 4000 calories. The fats
and carbohydrates appear to undergo complete oxidation in the body.

An important series of expeiiments on the sources of animal heat
has been performed by Eubner.^ The experiments were carried on for
several days in succession upon a dog weighing 12 kilos. The animal
was given a known amount of meat once a day ; the urine and fseces
were collected and their heat of combustion determined, and the heat
given off by the animal was measured by a calorimeter. At the same
time the discharge of carbon dioxide and water from the dog were deter-
mined, also the total nitrogen lost in the urine and fseces, and the loss
or gain in weight of the animal. No external work was done by the
dog, for it remained quiet in the calorimeter, and therefore no energy
was lost in the form of work.



The following is an example of the results obtained :







Date.


Condition.


Total Dis-
charge of
Nitrogen.


Carbon
from
Fat.


Heat
Calcu-
lated
from
Proteid.


Heat
Calcu-
lated
from
Fat.


Total Heat
in Twent3'-
four Hours.


16th October 1889


Fasting


3-06


16-38


77-0


201-5


278-5 kilo-cal.



This result, 278-5 kilo-calories, compares well with the heat, 276*8 kilo-
calories, given off by the animal in the calorimeter.



Date.


Condition.


Heat

given to

Calorimeter.


Heat

Lost in

Ventilation.


Heat Lost in

, Evaporation

of Water.


Total Heat
in Twenty-
four Hours.


16th October 1889


Fasting


213-2


17-6


45-9


276-8
kilo-cal.



Ztichr.f. Biol., Miinchen, 1893-94, Bd. xxx. S. 73.



836 ANIMAL HEAT.

Thus it is possible to calculate the production of heat in an animal, if the
quantity and nature of its food and the amount of the discharge of nitrogen in
the urine and faeces be known. This Rubner has done, and has compared the
result with the heat given off by the animal to a calorimeter. Thus :—

T-, , J. J , . , .T J f 228"06 grms. proteid.

iood 01 dog during \1 days= ^ o^a ^ zK

'^ ° -' ( 340-4 grms. fat.

In the urine 30 "0 grms. X were discharged, and the dry faeces amounted
to 16 '8 grms.

Calculation 1, fro'tn physiological heat values.

Proteid, 228-06 x 4-0 kilo-cal. = 912-24
Fat, 340-4 x 9-423 „ =3207-0



4119-2 kilo-cal. in 12 days.

Calculation 2, from physical heat value with reduction for heat value
of urine and foeces.

Proteid . . = 1222 kilo-cal.
Pat . . . =3207



4429



Q/\K (223 '5 heat value of urine.
OUO-/ \ 8X-7 ,, „ fgeces.



In 12 days 4124 kilo-calories.

The amount of heat actually given off by the dog during this time was
3958 kilo-calories. Thus the calorimeter showed that 96 per cent, of the
energy of the food had appeared as heat.

Ptecent work by Eubner^ has shown that the body of a living
animal may be looked upon as a calorimeter, and may be used as such
for the determination of the heat of combustion of food. Thus the heat
of combustion of 1 grm. of dry meat, determined in this way, is 4007
calories, that of 1 grm. of dry fat 9353 calories, figures which are practic-
ally the same as 4000 and 9423 respectively, the results obtained by
combustion in a Thompson's calorimeter, when allowance is made for
the heat value of the products of the proteid lost in the urine and
fteces.

The following is one of Rubner's examples of such a determination :— A
small dog fed upon meat discharged daily 10-09 grms. of nitrogen in its urine
and faeces, and 9-06 grms. carbon from fat underwent combustion. The heat
produced, as determined by the calorimeter, was 379-5 kilo-calories. On a diet
of meat and fat the same dog discharged 2-95 grms. of nitrogen, and 19-12 grms.
carbon from fat underwent combustion, while the production of heat was 311
kilo-calories. IS^ow, if the calorimetric value of the nitrogen be represented by
X and that of carbon from fat by y, then —

(1) 10-0903+ 9-06?/ = 379-5

(2) 2-95a;+19-127/ = 311-0

.-. a3 = 26'7 kilo-calories and y - 12-15 kilo-calories.

The results obtained by direct combustion Avere 26-0 and 12 '3 kilo-calories.



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