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tissues of warm-blooded animals are the seat of a very energetic
combustion, which is subject to quantitative and qualitative changes,
owing to the inliuence of certain factors, such as age, size of body,
external temperature, muscular activity, rest, digestion, hunger, and
hibernation. A general comparison between the various members of
the two great classes of the warm-blooded animals, birds and mammals,
will be found in the tables on pp. 706-708.

These tallies ^ show that, weight for weight, birds have a more
rapid respiratory exchange than mammals, and this difference is
associated with a higher bodily temperature.^ It is also to be
noticed that the respiratory quotient of the herbivorous animals is
nearly unity, but that of the carnivorous animals is about 0'74.
The respiratory exchange of small animals of the same or of
different species is relatively greater than that of large animals.^
The causes of many of these differences will now be discussed in
detail.

The influence of external temperature upon the respiratory ex-
change, — Since the time when Crawford * showed by experiment that
external cold increased the discharge of carbon dioxide from a warm-
blooded animal, numerous similar observations have been made by various
observers. The most important result of this work has been the dis-
covery that cold-blooded animals respond to changes of external tempera-
ture in an exactly opposite way to that shown by warm-blooded animals ;
in the former class a rise or fall in the temperature of the surroundings
produces respectively an increase or decrease in the intake of oxygen
and the output of carbon dioxide, whereas in the latter class cold increases
and heat diminishes the respiratory exchange. On this account it will
be well to consider separately the influence of temperature on these two
classes of animals, and then to discuss the causes of the great difference
in the effect.

Cold-blooded animals. — Some of the earliest experiments upon the
influence of temperature upon the respiratory exchange of cold-blooded
animals appear to have been made by Delaroche,^ Treviranus,^ and
Marchand,'^ but, owing to imperfect methods, their results are not very
exact, although they show that the respiratory exchange slowly rises
and falls wdth the external temperature.

In 1857, Moleschott^ made a series of experiments upon frogs, and
found that exposure to an increased external temperature or to light
caused an increase in the output of carbon dioxide.

Eegnault and Eeiset ^ made three observations upon the respiratory
exchange of green lizards at different external temperatures, and obtained
the following results : —

^ Further data will be found in the article by Zuntz, Hermann's " Haudbuch," Bd. iv.
Th. 2, S. 129, from which many of the figures in the above tables have been taken. See
also tables in paper by Richet, Arch, clc ;p]iysiol. norm, dpatli., Paris, 1891, tome xxiii.
p. 74.

- Article "Animal Heat," this Text-book, vol. i. jx 791.

^ See p. 720. ,

^ "On Animal Heat," London, 1788, pp. 311, 387.

° Journ. dcjth.ys. clc chim., etc., Paris, 1813, tome Ixxvii. p. 5.

•^ Ztschr.f. Physiol., 1831, Bd. iv. S. 1.

^ Journ. f. irrakt. Chem., Leipzig, Bd. xxxiii. S. 152.

® Uniersuch. z. JYaturl. d. Mensch. u. d. Thieve, 1857, Bd. ii. S. 315.

^ Ann. de chim. etphys., Paris, 1849, Ser. 3, tome xxvi.



7IO



CHEMISTR Y OF RESPIRATION.



Weight.


Oxygen

per Kilo, and

Hour.


Carbon Dioxide

per Kilo, and

Hour.


CO2
O2

-73
•71
-75


Nitrogen
discharged , Tempera-

per Kilo. \ ture.
and Hour, j


Remarks.


Grms.
3 lizards, 68-5

2 „ 42

3 ,, 62


Grms. C.c.
0-0246 17-2

0-0646 45-2

0-1916 134-0


Grms. C.c.
0-025 12-6

0-063 32-3

0-199 100-77


C.c.
5-732

1-905

2-49


7° -3
14°-8
23° -4


Hibernating.

Half awake.

Awake and well ;
fed for a month.



There are, however, several conditions which prevent these results
from being considered comparable ; the hibernating ^ animal has a very
low respiratory exchange, even when the external temperature is higher
than 7°*3 ; in the last experiment the food would increase the respira-
tory exchange ; the observations were made at intervals of several
months, and are complicated by the large discharge of nitrogen, which
is probably to be attributed to an error of experiment.'^

Biitschli ^ showed that the respiratory exchange of insects varied in
the same direction as the temperature of their surroundings.

The most complete series of observations appear to be those of
Schulz* upon the edible frog {Bana esculenta). The following table
gives his chief results, obtained upon frogs in summer : —



Temperature

of the Respiration

Chamber.


Temperature
of Frog.


C02-0utput

per Kilo, and Hour.

C.c. at 0° and 760 Mm.


C02-output

per Kilo, and Hour

in Grms.


o°-o


i°-o


4-31


0-0084


0°-25


i°-o?


6-097


0-0119


0°-8


l°-5


7-50


0-0147 ,


6°-l


6° -4


34-17


0-0672


15°-8


15°-4


35-30


0-0694


17°-0


15°-2


41-83


0-0822


25°-5


25° -0


76-26


0-1499


25°-5


25°-3


86-75


0-1706


33°-0


33°-0


279-40


0-5495


33°-2


33°-l


314-53


0-6179


34°-2


33°-5


340-48


0-6696


35°-0


34° -0


325-05


0-6392



It is to be noted that in Schulz's experiments the frogs were kept in
the warm or cold surroundings until their temperature was equal to
that of the air, so that the results are strictly upon frogs at different
temperatures. The response of a frog, as shown by its temperature and
respiratory exchange, to a change of external temperature is very slow,
and for this reason observations upon the metabolism of cold-blooded
animals can only be properly compared when the temperature of the
animal and that of the air are known. The above results show that at
temperatures a degree or two above zero the output of carbon dioxide



1 See "Animal Heat," this Text-book, vol. i.

" See also Pfliiger, Arch. f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S.

^ Arch. f. Aiiat., Physiol., u. wissensch, Med., 1874, S. 348,

^ Arch./, d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 78.



73.



WARM-BLOODED ANIMALS.



711



is very minute, and rises with the temperature, until at 34° the output
is, weight for weight of body, equal to that of a man.

The observations of Pembrey ^ and Vernon ^ seem to show that the
output of carbon dioxide in frogs {Puma temporia) does not increase in
exact proportion with the temperature.

"Warm-blooded animals. — Since the first experiments l)y Crawford,^
in which it was shown that a guinea-pig produced more carbon dioxide
in cold than in warm surroundings, numerous observations * have been



Animal.


Tempera-
ture of
Air.


Oxygen absorbed

per Kilo, and

Hour.


Carbon-Dioxide

discharged

per Kilo.

and Hour.


Water

discharged

per Kilo.

and Hour.


OO2
O2


CO2
H2O


Observer.








C.c.


C.c.










Guinea-pig


\


15°-5
6°-0


1079-66
1438-31


1065-92
1262-67




-98
■88




- Colasanti.^




f


22°-2


1050-00


867-19




-83




"


\


6°-3


1592-33


1230-00




-79








r


3°-64


1856-50


1554-80




-83




1 Finkler.6


;;


I


26°-21


1118-50


1057-40




-94










Grms.


Grms.


Grms.








r





9-030


9-505


6-705


•76


1-4


>


Mouse ;







8-384


8-641


6-721


-74


1-2




weight about-!


10°-5


6-660


7-443


5-079


-80


1-4


I Oddi.7


19 grms.




25°


4-862


5-400


5-102


-80


1-0








35°


5-912


4-977


4-736


•65


1-0


J


Pigeon


■{


-9°




3-016








Corin and Van


17°-5




1-141








Benedeu.^








Grms.


Grms.


Grms.






1




■\


-3°-2


21-39


22-03


14-12






]
'-CarlTheodor,«

J


Cat .


l°-3


17-73


18-92


10-87








18° -Q


12-30


13-93


10-60








29°-6


13-91


13-12


19-48






For periods of


six hours, cat weighing








2557-2650


grms. The figures are














not reduced


to kilo, and hour.









^ "Proc. Physiol. Soc," Journ. Physiol., Cambridge and London, 1894, vol. xvi.

^ Journ. Physiol., Cambridge and London, 1894-1895, vol. xvii. p. 277.

3 " On Animal Heat," London, 1788, pp. 311, 387.

^ Delaroche, Journ. de phys. de chini. etc., Paris, 1813, tome Ixxvii. p. 5 ; Vierordt,
■"Physiol, des Athmens," 1845; Wagner's " Handworterbuch, " 1844, Bd. ii. S. 828;
Letellier, Ann. de chim. etj^hys., Paris, 1845, Ser. 3, tome xiii. p. 478 ; Lehmann, Abhandl.
■d. k. sdchs. Gesellsch. d. JVissensch., Leipzig, 1846, S. 463 ; Liebermeister, Dcutsclies Arch.
/. Min. Med., Leipzig, 1872, Bd. x. S. 89, 420 ; Gildemeister, Virchoiv's Archiv, Bd. lii.
S. 130; Sanders-Ezn, Per. d. k. sdchs. Gesellsch. d. JVissensch. Hath. -phys. CL, Leipzig,
1867, S. 58 ; Rohrig and Zuntz, Arch. f. d. ges. Physiol., Bonn, 1871, Bd. iv. S. 57 ;
Pfliiger, ibid., 1876, Bd. xii. S. 282 ; Regnault and Reiset, Ann. d. Chem. x(,. Pharm.,
1850, Bd. Ixxiii. S. 260 ; BerthoUet, Mdm. de la Soc. de phys. et de chim. d'Arcueil, Paris,
tome ii. ; Senator, Arch. f. Anat., Physiol., u. wissensch. Med., 1872, S. 1 ; 1874, S. 42,
54; Centralbl. f. d. med. Wissensch., Berlin, 1871, Nos. 47 and 48 ; Erler, Arch. f. Anat.,
physioL, u. wissensch. Med., 1876, S. 556 ; Litten, Virchov}^s Archiv, 1877, Bd. Ixx. S. 10 ;
Fredericq, Arch, de bioL, Gaud, 1882, tome iii. pp. 736, 743 ; Quinquand, Compt. rend.
Acad. d. sc, Paris, 1887, tome civ. p. 1542.

5 Arch. f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 92. See also Pfliiger, ibid.^
B. 469.

^ Ibid., 1877, Bd. xv. S. 603.

■^ Arch. ital. de bioL, Turin, 1891, vol, xv. p. 223.

* Arch, de biol.. Gaud, 1887, tome vii. p. 265.

^ Ztschr.f. Biol., Miinchen, 1878, Bd. xiv. S. 51.



7 1 2 CHE MIS TR Y OF RESPIRA TION.

made upon the influence of external temperature upon the respiratory
exchange of warm-blooded animals. The general result of this work is
that the intake of oxygen and the output of carbon dioxide increase
with a fall and decrease with a rise of external temperature. This is
shown by the examples, which have been taken from the results obtained
by different observers, and are given in the preceding table.

It appears that, when the external temperature is raised to a point
about 30°, the respiratory exchange shows an increase above the amount
observed at a temperature of 20°. Thus Voit ^ found in the case of a
man, that the output of carbon dioxide was increased by a fall of 9° or
10" below the average temperature 14°— 15°, and also increased by a rise
of 15° or 16° above that point; the augmentation in the discharge of
carbon dioxide was respectively 36 per cent, and 10 per cent, above that
given off at 14°-15°. A similar result was obtained by Page,^ who
found that at a temperature of 25° the discharge of carbon dioxide by a
dog was at a minimum ; a fall or rise of 10° below that point produced a
mean increase of 31 per cent, and 51 per cent, respectively.^ Unfortun-
ately Voit gives no details as to the temperature of the man during
the experiments, but in one or two cases Page notes that the tempera-
ture of the dog was raised above the normal by exposure to the
warm air.

The earhest experiments upon the influence of external temperature
on the respiratory exchange of man were made by Lavoisier and Seguin,"^
who found that a man at rest absorbed ui an hour 3449 grms. of
oxygen when the air was 32°-5, but 38*31 grms. when the temperature
was 15°. Since that time many observations^ have been made upon
man and the effect of external temperature on his respiratory exchange,
and of these the most important are those made by Lowy.*^ The
general result drawn from his experiments is that the effect of external
cold varies in different men. Out of fifty-five experiments, the oxygen
absorbed was increased above 5 per cent, in twenty-six cases, unaltered in
twenty, and diminished in nine cases. In these experiments, in which the
metabolism was increased, for the variations in the output of carbon
dioxide followed those in the absorption of oxygen, the heights to which
it was raised varied between 5 and 90 "8 per cent, above the normal. A
point worthy of note is that the greatest increase in the respiratory
exchange was observed in the men who shivered or moved when they
felt cold, and that the respiratory exchange remained unaltered or
decreased in the men who, notwithstanding the sensation of cold,
remained quiet, and by an effort of the wall suppressed any tendency to
move or shiver. Lowy concludes that the only involuntary regulator
of temperature in a man exposed to moderate cold is the skin. It must
be pointed out, however, that increased muscular activity in a man who

1 Ztschr.f. Biol., Miinchen, 1878, Bd. xiv. S. 80.

"^ Journ. Physiol., Cambridge and London, 1879-80, vol. ii. p. 228.

■'See also Rubner, " Biologische Gesetze," Universitats-]Drogi-amni, Marburg, 1887;
abstract in Centralld. f. Physiol., Leipzig n. Wien, 1887, S. 700.

■* "(Euvres de Lavoisier," tome ii. pji. 688, 704 ; Hist. Acad. ray. d. sc, Paris, 1789,
p. 575. See also Pep. Brit. Ass. Adv. Sc, London, 1871, p. 189.

5 Vierordt, "Phj-siol. des Athmens," 1845; E. Smith, Phil. Trans., London, 1859,
vol. cxlix., p. 681 ; Speck, Schrift. d. Gcsdlsch. ::. BcfiJrd. d. ges. Naturw. zu Marburg,
1871, Bd. X. ; Liebermeister, D cut sches Arch. f. klin. Med., Leipzig, 1872, Bd. x. S. 89,
420 ; Lehmann, Fircho7v's Archiv, 1873, Bd. Iviii. S. 92. Johansson, Skandin. Arch. /.
Physiol., Leipzig, 1897, Bd. vii. S. 123.

^ Arch./, d. yes. P'hysiol., Bonn, 1890, Bd. xlvi. S. 189.



WARM-BL O ODED ANIMALS. 7 1 3

feels cold, is not necessarily brought about by a conscious effort of the
will ; it is to a great extent reflex, and shows itself in the more energetic
performance of work, or, if no work be done, the reflex may become so
imperative as to give rise to involuntary movement, shivering, which is
only of value to the organism as a source of greatly increased heat
production. There is little doubt but that a normal man, who feels cold
and is free to follow the dictates of his sensations, will be more active,
and will produce more carbon dioxide and absorb more oxygen than he
would in warm surroundings. The man who suppresses increased
muscular action when he feels cold, is abnormal. It follows, therefore,
that man is no exception to the general rule that warm-blooded animals
in cold surroundings increase, in warm surroundings diminish, their
respiratory exchange and production of heat.

It has already been shown that a rise or fall in external temperature
determines in the same direction a variation of the respiratory exchange
of cold-blooded animals. What, then, is the cause of the totally opposite
result observed in warm-blooded animals ? To this question only an
incomplete answer can be given. The difference is due to the nervous and
muscular mechanisms which maintain the fairly constant temperature
observed in the warm-blooded animals. For if, as Sanders-Ezn^ and
Pfliiger ^ have shown, the exposure to cold be excessive, and the animal's
temperature falls to 26°, then also there is a fall in the intake of oxygen
and the output of carbon dioxide ; on the other hand, if by means of
warm baths the internal temperature of the animal is raised above the
normal, then there is an increase above the average respiratory exchange.
In fact, a warm-blooded animal responds to a rise or fall in the tempera-
ture of its surroundings with a decrease or increase of its metabolism,
only as long as its internal temperature remains near the normal point.
Moreover, Pfliiger has proved the connection between the normal
response to a change of external temperature and the nervo-muscular
system, for he shows that a mammal paralysed with curari ^ or with its
spinal cord cut in the lower cervical region, absorbs more oxygen and
discharges more carbon dioxide in warm than in cold surroundings ; it
resembles in this respect a cold-blooded animal. A similar cold-l)looded
condition can be produced in mammals, as Eumpf,* Eichet,^ and
Pembrey^ have observed, by exposing the anaesthetised animal to
changes of temperature.

The objection that these experiments are associated with markedly
abnormal conditions, and therefore cannot indicate the true condition of
normal animals, is met by the fact that it is possible to trace the
gradual development of the means whereby an animal increases or
decreases its metabolism and maintains a fairly constant heat of its
body, notwithstanding wide variations in the temperature of its
surroundings. This has been shown by Pembrey'^ in a series of
comparative experiments upon full-grown and newly-born animals. In
the full-grown mouse the response to a change of external temperature

^ Ber. d. k. sacks. Gesellsch. d. Wissensch. Math.-iiliys. KL, Leipzig, 1867, S. 58.
- Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xviii. S. 247.
'■^ See also Zuntz, Arch. f. d. ges. Physiol.. Bonn, 1876, Bd. xii. S. 522.
^ Ibid., 1884, Bd. xxxiii. S. 538.

•'' Compt. rend. Acad. d. sc, Paris, 1889, tome cix. p. 190.

" "Proc. Physiol. Soc," Journ. Physiol., Cambridge and London, 1894-95, vol. xvii.
'^ Journ. Physiol., Cambridge and London, 1894, vol. xv. p. 401; 1895, vol. xviii.
p. 363.



7^4



CHEMISTR Y OF RESPIRA TION.



is almost immediate. The contrast in the case of young mice of
different ages is shown by the fact that a fall in external tempera-
ture produces a fall in the output of carbon dioxide, and in the
temperature of the young mouse, until it is about nine days old, when
it begins to respond in a similar way to that observed in a full-grown
animal.

A similar development can be observed in other young animals born
in an immature condition, and in the chick ^ before and after it is
hatched, but a marked contrast is found in young animals born with a
well-developed and active body.^

The influence of miiscTolar activity upon the respiratory ex-
change. — Muscular activity greatly increases the rate of breathing, the
intake of oxygen, and the output of carbon dioxide. It was but natural,
therefore, that physiologists should attribute the hyperpnoea caused by
excessive muscular exertion to a deficiency of oxygen, or to an accumula-
tion of carbon dioxide in the blood, consequent upon the greatly increased
metabolism. This theory, however, has been proved by experiment to
be erroneous. Mathieu and Urbain^ determined the gases present m
samples of blood removed from an animal after a period of rest, and
again after a period of activity, and they found as a general result an
increase in the oxygen, and a decrease in the carbon dioxide of the
blood in the latter condition. Their analyses, however, were subject to
certain sources of error. The question has been more thoroughly
investigated by Geppert and Zuntz,* who found that muscular activity
is indeed accompanied by an increase in the oxygen and a decrease in
the carbon dioxide of the blood, and that the hyperpnoea is probably due to
some product of muscular activity which is absorbed by the blood and
carried to the medulla oblongata, where it stimulates the respiratory
centre. The chief evidence for these statements will now be given.
After section of the spinal cord of a dog in the dorsal region, tetanisation
of the hind limbs causes an increase in the air inspired, in the intake of
oxygen, and in the output of carbon dioxide.^



Dog iveighing 2100 Grms.



Volume of Air inspired
per Minute.


Intake of Oxygen.


Output of Carbon Dioxide.


CO,


Condition.


1012 c.c.


Per Kilo. Bod
20-4 c.c.


y Weight and per Minute.
18-2 C.C.


•89


Rest.


2148 ,,


36-8 ,,


31-8 ,,


•86


Tetanus.


86.3 „


21-6 „


16-2 „


•75


Rest.


1326 ,,


29-5 „


19-8 ,,


•66


Tetanus.



^ Pembrey, Gordon, and Warren, Journ. Physiol., Cambridge and London, 1894-95,
vol. xvii. p. 331.

^ See also "Animal Heat," this Text-book, vol. i. p. 803.

^ Arch, dc physiol. norm, ct ^jath., Paris, 1871-72, tome iv. ; Compt. rend. Acad. d. sc,
Paris, 1872, tome Ixxiv. p. 190.

■* Arch.f. d. rjes. Physiol., Bonn, 1888, Bd. xlii. S. 189.

'' See also Hanriot and Richet, Compt. rend. Acad. d. sc, Paris, 1888, p. 75.



INFLUENCE OF MUSCULAR ACTIVITY.



715



Analyses of the gases of blood taken from an animal after voluntary
or involuntary muscular exertion show an increase in the oxygen and a
decrease in the carbon dioxide.



Gases of the Arterial Blood.



Oxygen
Volumes Per Cent.


Carbon Dioxide
Volumes Per Cent.


Animal.


Rest.


Activitj'.


Rest.


Activity.


17-58
17-33
15-88


17-68
More than 16-04


38 -57

36-49
53-71


35-01 (
39-06


Dog.

Rabbit.



Further, if the aorta be compressed in order to shut out the blood
from the stimulated limbs, no hyperpnoea is caused by the muscular
activity ; section of the vagi, sympathetic and recurrent nerves, or
section of the cord high up, does not prevent the stimulating effect of
muscular exertion upon the respiratory centre. In rabbits the alkalinity
of the blood is diminished by the acid formed during tetanic muscular
activity, and this is probably a cause of the decrease in the carbon
dioxide of the blood. No alteration could be found in the tension of the
oxygen and carbon dioxide present in the blood removed from an
animal after muscular exertion.^

Lehmann^ has shown that the injection of normal solution of
tartaric acid stimulates and quickens the respiration of a rabbit, whereas
a normal solution of sodium hydrate depresses the respiratory centre.
According to Lowy's^ experiments, the unknown substance which
stimulates the respiratory centre during muscular activity is not
excreted by the kidneys, and is not carbon dioxide ; for whereas the rate
of respiration is doubled by muscular work when the increase above the
normal amount of carbon dioxide in the expired air is only O'S per cent.,
yet the same amount of dyspnoea can be produced during rest only by
artificially raising the percentage of carbon dioxide to a much higher
point, about 5 per cent.

The credit of the discovery that work is associated with an increase
in the respiratory exchange, is due to Lavoisier,^ who, in a series of
experiments with Seguin, found that a man at work absorbed 91-2
grms. of oxygen in an hour, whereas at rest he only absorbed 38-3
grms. Although Vierordt^ and Scharling ^ both observed a similar
increase in the output of carbon dioxide in men at work, the first
series of careful experiments on the subject were those performed by

1 For criticism see Speck, BeutschesArch.f. klin. Med., Leipzig, 1891, Bd. xlvii. S. 509 ;
for reply by Zimtz and Geppert, ihid., 1891, Bd. xlviii. S. 444.

- Arch./, d. ges. Physiol., Bonn, 1888, Bd. xlii. S. 284.

3 Ihid., S. 281 ; 1890, Bd. xlvii. S. 601.

'^ Hist. Acad. roy. d. sc, Paris, 1789, p. 185 ; " CEuvres de Lavoisier," tome ii. pp. 688-
696.

^"Physiol, des Atlimens," Karlsruhe, 1845; Arch. f. physioL HeilTc., Stuttgart,
Bd. iii. S. 536 ; Wagner's " Handworterbuch d. Physiol.," 1844, Bd. ii. S. 828.

" Ann. d. Chem. u. Pharm., 1843, Bd. xlv. S. 214 : Journ. f. nraht. Chem., Leipzig,
Bd. xlviii. S. 435. . F fe'



7i6



CHEMISTR Y OF RESPIRATION.



E. Smith.^ He found that a man produced 161-6 c.c. of carbon dioxide per
minute when he was perfectly at rest, as in a deep sleep ; that during a
walk at the rate of two miles (3048 metres) an hour, the discharge of
carbon dioxide was increased to 569'5 c.c, and to 851"2 c.c. when the
rate of walking was quickened to three miles (4571"9 metres) an hour.
The greatest increase, 1581'9 c.c. of carbon dioxide per minute, was
caused by work upon a treadmill.

In 1866, Pettenkofer and Voit ^ performed a series of important
observations upon the metabolism of healthy men, under different con-
ditions as regards work and diet, and they found that if unity represent
the value of the output of carbon dioxide and the intake of oxygen
when the man is at rest, then work brings about the following
results : —

Carbon dioxide
Oxygen . . .

The numerous experiments made by Speck,^ under different con-
ditions as regards the amount and nature of the work performed, show
that the air inspired, the oxygen absorbed, and the carbon dioxide
discharged, are greatly increased ; the percentage composition of the
expired air is but little altered, and the respiratory quotient increases
slightly during the work. Hanriot and Eichet* find for each kilo-



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