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rest, but, directly marked exertion is necessary, the anaemic subject becomes
breathless ; he has no reserve upon which to draw during the greatly aug-
mented metabolism Avhich accompanies muscular work.

Nitrogen. — This gas appears to be quite inactive, and an animal
confined in it dies from want of oxygen. The same seems to be true
for argon. Nitrogen containing 5 per cent, oxygen was found by Sir
George Johnson ^ to produce satisfactory ansesthesia in man within a
minute ; this result is also to be attributed to want of oxygen.

The question of the absorption or discharge of nitrogen by the lungs
has been discussed in another part of this work.

Hydrogen. — -Numerous experiments have been made upon the
effects of respiring hydrogen, and the general conclusion is that it
produces no specific effect, but acts only by the exclusion of oxygen.^
Lavoisier and Seguin found that guinea-pigs respired in a normal
manner in a mixture of equal parts of oxygen and hydrogen, and similar
results were obtained upon dogs, rabbits, and frogs by Eegnault and
Eeiset. Many cold-blooded animals can live for several hours in pure
hydrogen.^

Carbon dioxide. — This gas in an undiluted state is irrespirable on
account of the spasm of the glottis which it occasions,* but when suffi-
ciently diluted with air or oxygen it can be respired, and produces head-
ache, slight giddiness, drowsiness, and hyperpnoea. Some of the earliest
experiments with this gas were made by Priestley,^ who found that cats
died from suffocation when placed in carbon dioxide, and butterflies when
held over the fermenting hquor in a brewery became motionless in a few
minutes, but revived on being brought into the fresh air. Since that
time numerous experiments have been made by different observers,^
especially by Paul Bert, whose results will be mentioned later. Brown-
Sequard and d'Arsonval'' state that they were able to breathe air
containing 20 per cent, of pure carbon dioxide for two hours without
any marked distress, but it is probable that there was some error in this
observation, for Haldane and Lorrain Smith ^ found that when they
breathed air containing 18-6 per cent, of this gas the following effects
were produced within a minute or two — hyperpnoea, distress, flushing,
cyanosis, and mental confusion. Haldane ^ has further investigated this
gas in connection with the suffocative gas found in wells and the
" black-damp " of mines.

^ Lancet, London, 1891, vol. i.

- Scheele, "On Air and Fire," trans, by Forster, London, 1780, p. 160; Fontana,
Phil. Trans., London, 1779, vol. Lxix. p. 337 ; Journ. dc phys., Paris, tome xv. p. 99 ;
Pilatre de Rozier, ibid., tome xxviii. p. 425 ; Lavoisier, Hist. Acad. roij. d. sc, Paris, 1789,
p. 574; H. Davy, '■Researches," p. 465 ; Allan and Pejiys, Phil. Trans., London, 1809,
p. 421.

^ Spallanzani, Edwards, Johannes Mliller. See this article, p. 781.

* Pilatre de Rozier, Journ. dephys., Paris, tome xxviii. p. 422.

^ Phil. Trans., London, 1772, vol. Ixii. p. 147.

^ For references, see Benedicenti, Arch. f. Physiol., Leipzig, 1896, S. 408.

'' Compt. rend. Acad. d. sc, Paris, 1889, lltli Feb.

^ Jotirn. Path, and Bacterial., Edin. and London, 1892, vol. i. p. 175.

^ Trans. Fed. Inst, of Minin.g Engineers, 1895, vol. viii. p. 549. "The Causes of Death
in Colliery Explosions," Government Blue Book, 1896.



740 CHEMISTR Y OF RESPIRA TION.

Speck 1 found, when he breathed a mixture of gases containmg 11 '51
per cent, of carbon dioxide, that 528 c.c. carbon dioxide were absorbed by
the blood in a minute, whereas under normal conditions 230 c.c. of that
gas would have been discharged. In a dog Pfiiiger ^ found that there
were, under normal conditions, 29 '8 volumes per cent, carbon dioxide^
in the arterial blood, but 56*8 volumes per cent, after the dog had
breathed for one minute a mixture containing 70 per cent, oxygen
and 30 per cent, carbon dioxide. Zuntz * observed an increase to
89 '6 volumes per cent, carbon dioxide when a dog breathed for one
minute and a half a mixture containing 3 6 '9 per cent, carbon dioxide.

Numerous experiments were made by Paul Bert ^ upon the action of
this gas upon different forms of hfe. He found that a percentage of 13 "5
to 17 was fatal for reptiles, 24 to 28 for sparrows, and 30 or more for
mammals. When the air contained 30 to 40 per cent, of carbon ■ dioxide,
death resulted owing to the high tension of the gas in the blood ; thus in
some dogs the percentage of carbon dioxide in the arterial blood was
116, in the venous blood 120. Complete insensibility could be produced
long before any danger to hfe arose, and thus the gas mixed with air
or oxygen could Ije used for the production of antesthesia.^

Carbon monoxide, — The physiological action of this gas is of the
utmost practical importance, since it is every year the cause of
numerous deaths in cases of poisoning from coal gas, the fumes of kilns
and coke fires, and in the air of coal mines, especially after explosions.
Although it has long been known that carbon monoxide is poisonous,
it was about the year 1857 that Claude Bernard '' and Hoppe-Seyler ^
first pointed out that the carbon monoxide displaced the oxygen of
the blood by forming a more stable compound with haemoglobin, and
thus brought about asphyxia.^ The action of this gas has been studied
by many observers.^*'

The most recent investigations are those of Haldane,^^ who has
exyjerimented both upon himself and upon mice. The following are his
chief conclusions :• — ^The symptoms produced in man do not become
sensible until sufficient carbonic oxide has been absorbed for the
corpuscles to become about a third saturated ; with half saturation of
the corpuscles the symptoms become urgent. The symptoms are due
solely to deficiency in the percentage of oxygen in the blood, and are
similar to those experienced by mountaineers and balloonists at high
altitudes. The time required for the symptoms to appear in different
animals is proportional to the respiratory exchange jjer unit of body weight,
and is about twenty times as long in a man as in a mouse. Hence
it is possible with safety to use a mouse as an indicator of the presence
of poisonous proportions of carbonic oxide in the atmosphere of a coal-

^ Centralbl.f. d. med. Wisscnsch., Berlin, 1876, No. 17.

2 Arch.f. d. ges. Physiol., Bonn, 1868, Bd. i. S. 103.

^ Measured at 0° and 1 m.

^Arch.f. d. ges. Physiol., Bonn, 1888, Bd. xlii. S. 408.

^ "La pression baronK^trique," Paris, 1878, p. 982. This article, pp. 743-45.

® See also Grc^hant, Compt. rend. Soc. de hiol., Paris, 1887, p. 542.

"^ "Le9ons siir les effets des substances toxiques et niMicamenteuses," Paris, 1857, p.
184 ; "Lecons sur les liquides de Forganisme, " Paris, 1859, tome i. p. 365 ; tome ii. p. 427.

8 Virchoiv's Archiv, Bd. xi. S. 228 ; Bd. xiii. S. 104.

^ This Text-book, article " Hiemoglobin."

^^ Gaglio, Arch. /. expe7'. Path. ti. Pharmacol., Leijizig, 1887, Bd. xxii. S. 233 ; Gruber,
Arch.f. Hyg., Munchen u. Leipzig, 1883, Bd. i. S. 145; Welitschkowsky, ibid., S. 210;
Pokker, ibid., S. 503 ; Gr^hant, "Les poisons de I'air," Paris, 1890.

" Journ. Physiol., Cambridge and London, 1895, vol. xviii. p. 430.



AIR VITIATED BY BREATHING.



741



mine. Distinct symptoms are produced by air containing "05 per cent,
of the gas, and urgent symptoms with '2 per cent. The poisonous
action diminishes as the tension of oxygen increases, and vice, versd. At a
tension of two atmospheres of oxygen this poisonous action is abolished
in the case of mice, and this disappearance of the poisonous action is
due to the fact that at high tensions of oxygen the animals can dispense
entirely with the oxygen-carrying function of hfemoglobin, and can
obtain enough oxygen from the gas dissolved in the plasma of the
blood.

As regards the gases of the blood, after poisoning with carbon
monoxide, Grehant^ found that 100 c.c. of blood from the carotid of a
poisoned dog contained 6 c.c. of oxygen, 30"3 c.c. of carbon dioxide, and
20 c.c. of carbon monoxide ; whereas a sample of blood taken before the
administration of the gas yielded 19 '5 c.c. of oxygen and 44'2 c.c. of
carbon dioxide. The following figures show the effect of different doses
of carbon monoxide upon the gases of the blood of dogs poisoned by the
Ras : —



CO IN Inspired Air.


Gases of Blood.


C0„.


Go.


N.


CO.


1 in 1000 .
1 ,, 2000 .
1 ,, 3000 .
1 ,, 4000 .


28-9p. ct.
51-8 ,,
42-2 ,,
40-4 „


12-2 p. ct.
15-5 ,,
13-4 ,,
21-5 ,,


1"5 p. ct.
1-5 ,,
1-8 ,,
1-5 ,,


5 '5 p. ct.
2-8 „
1-7 „
1-3 „



The administration of small doses of carbon monoxide, enough to
produce unconsciousness, causes a marked reduction in the respiratory
exchange ^ of a mouse, and its temperature falls.

According to Gaglio,^ carbon monoxide present in the blood is not
oxidised, but St. Martin^ states that it is slowly oxidised in the
presence of oxyhtemoglobin. The compound of this gas with hsemo-
globin is partly dissociated in sunlight,^ but upon these points more
details will be given in the discussion upon the gases of the blood.

The respiration of air vitiated by breathing.— The air vitiated
by respiration, as in overcrowded rooms, is distinctly unwholesome, but
the causes of this deleterious action are not simple, but may arise from
substances given off either from the lungs by respiration, from the body
by perspiration, or from the injurious products of disease or filth.

Even as early as 1674, Mayow^ had stated that an animal died if
kept in a limited quantity of air, because it had used up the respirable
portion, the nitro-aerial gas (oxygen) ; he further pointed out that re-
spiration and combustion produced similar changes in the air. About
the year 1726, Stephen Hales '^ observed by experiments upon himself

^ Comxit. rend. Soc. de iioL, Paris, 1892, p. 163.

^ Haldane, Journ. Physiol., Cambridge and London, 1895, vol. xviii. p. 430.

^ Arch. f. exper. Path. u. Pharmakol., Leipzig, 1887, Bd. xxii. S. 233.

^ Comft. rend. Acad. d. sc, Paris, 1891, tome cxii. p. 1232.

^ Haldane, loc. cit.

^ " Tractatus quinqne," Oxonii, 1674.

■^ "Statical Essays," 2nd edition, vol. i. p. 236 ei seq.



742 CHEMISTR Y OF RESPIRA TION.

that the " noxious vapours " produced by repeatedly breathuig the same
air could be removed by potash, and the air rendered fit for respira-
tion. A few years later, Black ^ showed that the " noxious vapours "
were carbon dioxide.

The importance of the several factors mentioned above has been differ-
ently estimated by various observers.'^ Brown-Sequard and d'Arsonval ^
concluded that volatile poisons were given off from the lungs of healthy
men and animals, for they found that the condensed vapour of breath
caused death when injected into rabbits ; that rabbits made to breathe
air vitiated by the respiration of other rabbits until the carbon dioxide
was 2 to 6 per cent., died, unless the supposed volatile poisons were
removed by previously passing the air over pumice soaked in sulphuric
acid ; that no bad effects were produced when men breathed for an
hour or two air containing 20 per cent, of pure carbon dioxide.
The experiment of injecting the condensed vapour of breath has been
repeated by Dastre and Loye,* Hoffmann- Wellenhof,^ Lipari and Crisa-
fulli,^ and Lehmann and Jessen,'^ but the results were negative.

Eichardson ^ maintained that breathed air was poisonous, even though
all the carbon dioxide and other impurities had been removed ; the cause
he considered to be " Glevitalised oxygen," whatever that term may mean.
Jackson ^ thought that carbon monoxide was the poison. From experi-
ments performed upon himself, Angus Smith '^^ concluded that air vitiated
by respiration until it contained 1 per cent, carbon dioxide, produced
distinct feelings of discomfort.

Experiments, however, performed by Hermans ^^ have shown that
no volatile poisons are given off by respiration, and more recently
Haldane and Lorrain Smith,^'-^ in an investigation of the subject, both
as regards animals and men, have confirmed and extended Hermans'
work. The following are the chief conclusions given by Haldane and
Lorrain Smith : —

" 1. The immediate dangers from breathing air highly vitiated by
respiration arise entirely from the excess of carbon dioxide and
deficiency of oxygen, and not from any special poison.

" 2. The hyperpnoea is due to excess of carbon dioxide, and is not
appreciably affected by the corresponding deficiency of oxygen. The
hyperpnrea begins to appear when the carbon dioxide rises to from
3 to 4 per cent. At about 10 per cent, there is extreme distress.

" 3. Excess of carbon dioxide is likewise the cause, or at least one
cause, of the frontal headache produced by highly vitiated air.

" 4. Hyperpnoea from defect of oxygen begins to be appreciable when
the oxygen in the air breathed has fallen to a point which seems to

^ "Lectures on Chemistry," ed. Robison, Edinburgh, 1803.

- See Merkel, Arch. f. Hyg., Miinchen u. Leipzig, 1892, Bd. xv. S. 1, where further
references are given.

" Compt. rend. Acad. d. sc, Paris, 1888, tome cvi. pp. 106. 165 ; Compt. rend. Soc. de
hioJ., Paris, 1887, p. 814 ; 1888, pp. 33, 90, 99, 151.

* Ibid., 1888, i)p. 43 and 91.

° Wien. Iclin. JVchnschr., December 13, 1888.

c Bull. gen. de iherap. etc., Paris, 1889, No. 46, p. 524.

■^ Arch./. Hyg., Miinclien u. Leipzig, 1890, Bd. x. S. 367.

^ Brit. Med. Journ., London, 1860, vol. ii. ; Chcm. JVeim, London, vol. Iv. p. 253.

® " Proc. Physiol. Soc," December, 1887, in Jvurn. Physiol., Cambridge and Loudon,
vol. ix.

^" "Air and Rain," ]). 130.

" Arch./. Hyg., Miinchen u. Leipzig, 1883, Bd. i.

^'■^ Journ. Putli: and Barteriol., Edin. and London, 1892, vol. i. p. 175.



ASPHYXIA IN A LIMITED QUANTITY OF AIR. 743



differ in different individuals. In one case the hyperpnoea became
appreciable at about 12 per cent., and excessive at about 6 per cent."

These observers also point out that the odorous substances arising
from want of cleanliness of the body or the room, are also causes of the
discomfort experienced in breathing the air of an overcrowded room.

The causes of asphyxia in a limited quantity of air.— A
warm-blooded animal confined in a limited quantity of air soon gives
signs of discomfort ; it becomes restless, breathes more rapidly, and
soon pants for breath. This stage is succeeded by one during which
the animal is quieter, breathes more slowly but more deeply ; it becomes
less sensitive, and falls down ; agonising efforts are made to breathe, the
nostrils are dilated, and the mouth is open. The animal now becomes
unconscious, its pupils are dilated, it gives a few slight and irregular
respirations, it is seized by convulsions, and then, after a slight pause, its
limbs are stretched out with a convulsive shivering movement, its head
is thrown back, and it dies.

The general phenomena of asphyxia are described elsewhere in this
work ; ^ here it is necessary to consider only the chemical changes in the
air, the alterations they produce in the respiratory exchange of the
animal, and how they cause its death. Upon these questions numerous
experiments have been made.^

The duration of life in a limited quantity of air depends upon
various conditions, such as the amount and temperature of the air, the
nature and age of the animal. The following table of some of Paul
Bert's experiments will illustrate the influence of some of the above con-
ditions, and will show the composition of the air at the time of death : —











Percentage Composi-










tion of Air at tlie


Animal.


Tempera-
ture of Air.


Volume
of Air.


Duration of Life.


time of Death.


O2.


CO2.


Mammals —












Cat, 1850 grms.


25°


5000 C.C.


25 min.


3-4


17-1


Kitten, 5 days old, 130


15°


1000 ,,


^\ to 6| hrs.


2-0


16-6


grms.












Kitten, 24 hours old, 125


11°


435 „


1 hr. 15 min.


3-0


14-S


grms.












Hedgehog, young, 115


25°


1500 ,,


1 hr. 15 min.


4-0


14-0


grms.












Dormouse, hibernating.


12°


350 ,,


About 1 day


2-2


14-6


50 grms.












Eat, white, 115 grms. .


14°


450 ,,


32 min.


3-0


11-0


,, 125 ,,


25°


1600 ,,


Between 2 and
3. hrs.


2'2


17-8


,, ,, adult


30°-35°


2000 ,,


20 min.


11-8


6-5


,, three days old,


25°


loo ,,


More than 6 hrs.


0-75


17-0


5 grms.












Rabbit, young, 200 grms.


25°


6000 „


Alive but insensi-
ble after 6 hrs.


1-9


13-4


Birds—












Sparrow, 23 grms.


16°


300 ,,


1 hr.


2-3


13-3


Finch, 25 grms.


11°


428 „


21 min.


5-0


12-4



^ Article " Mechanism of Respiration," this Text-book, vol. ii.

^Edwards, " De I'influence des agens physiques sur la vie," Paris, 1824; Collard de



744



CHEMISTR Y OF RESPIRA TION.



Before any conclusions are drawn from the results given in the
foregoing table, it will be advisable to consider the cause or causes of
death in these cases of asphyxia. Do the animals die from a want of
oxygen, or are they poisoned by the accumulation of carbon dioxide ?
In order to answer this question, experiments have been made on the
duration of life of animals confined in air containing an excess of
oxygen, or an excess of both oxygen and carbon dioxide. Many
observations have been made by various physiologists, but the most
complete are those of Paul Bert.^ The following table gives some of
his results : —



An Atmosphere containing an Excess of Oxygen.



Animal.


Tempera-
ture of
Gases.


Volume of
Gases.


Percentage
Composition of

Gases before
the Experiment.


Duration of Life.


Composition of

Gases at the

time of Death.






0„.


N.




C0„.


o„.


"Waem-Blooded—
















Cat, young, 250


25°


1800 c.c.


55-5


44-5


3 hrs. 25 min.


31


16


grms.
















E,at, adult, 80


ir


500 ,,


77


23


1 lir. 45 min.


20


50


grms.
















Rat, 6 weeks old.


25°


555 ,,


66


34


2 hrs.


29-5


26


50 grms.
Rat, 4 days old .


22°


120 ,,


81


19


18 hrs. 30 min.


28-5




Rabbit, young,


22°


1400 ,,


71


29


More than 5 hrs.


43-5


11


20U grms.
















Sparrow, young


25°


750 ,,


76


24


More than 5 hrs.


29




Cold-Blooded —
















Grass snake




875 ,,


77


23


8 days


13-5


61


Grey lizard


27°-29°


570 ,,


79


21


70 hrs.


15-7




Toad


6°-7°


400 ,,


100




7 days


17


81


Frogs


6°-7°


400 ,,


100




9 days


13-7


8



A consideration of the following results leads to the conclusion, held
by Mayow ^ as early as 1674, that a warm-blooded animal confined in a
limited quantity of air dies from the want of oxygen, and this con-
clusion is sup]jorted by the fact that its blood is markedly venous
and contains little or no oxygen. The percentages of oxygen and of
carbon dioxide in the air at the time of death are about 3 and
15 respectively. On the other hand, when there is in the air an
abnormal excess of oxygen, and at the same time a great augmenta-
tion of carbon dioxide, the warm-blooded animal dies from poisoning
with carbon dioxide, and here again the conclusion is strengthened b}^

Martigny, Arch. gm. de mecL, Paris, 1827, tome xiv. p. 203 ; Snow, JSdin. Med.
Journ., 1846, vol. Ixv. p. 49; Claude Bernard, "Lecons sur les effets des substances
toxiques et medicamenteuses," Paris, 1857 ; W. Milller, Ann. d. Cham. u. Pharm., 1858,
]>d. cviii. S. 257 ; Valentin, Ztschr. f. rat. Med., 1861, Bd. x. S. 33 ; Beau, Arch. gt'n. de
vied., Paris, 1860, Ser. 5, tome xvi. p. 64 ; 1864, Ser. 6, tome iii. p. 1 ; Paul Bert,
"Lecons sur la physiol. comp. de la respiration," Paris, 1870, p. 510.

^ "Le9ons sur la physiol. comp. de la respiration," Paris, 1870, p. 518.

^ " Tractatus quinque," Oxonii, 1674. See also this article, p. 741.



ASPHYXIA IN A IIMITED QUANTITY OF AIR.



745



the fact that the blood of the animal is generally arterial in colour.^
The fatal amount of carbon dioxide appears to be about 25 per cent.



An Atmosphere containing an Excess of Oxygen and of Carbon Dioxide.



Animal.


Tempera-
ture of
Gases.


Volume of
Gases.


Percentage

Composition

of Gases before

the Experiment.


Duration of Life.


Composition
of Gases at the
time of Death.


0.,.


CO..


COj.


0.


Warm-Blooded —
Rat, 1 month old.

32 grms.
Rat, 1 month old
. Rat, 3 days old,
5 grms.
Mouse, young,
5 grms.

Cold-Blooded —
Grey lizard
Frog- .


25°

25°
25°

22°

25°-29
25°-29°


550 c.c.

600 ,,

150 ,,

235 „

550 ,,
550 ,,


90

75
80

90

90
90


10

25
20

10

10
10


4 hrs.

20 min.
More than 5 hrs.

More than 5 hrs.

26 hrs.
20 „


22-5

26-5
29-5

24-5

16
17


77-5
73-5



In the cold-blooded animals a marked difference is observed ; death
in such experiments is generally due to an excess of carbon dioxide, and
the fatal percentage, about 16, is much lower than in the case of the
v^arm-blooded animals.

Important differences have also been observed by Edwards^ and
Paul Bert ^ in the duration of life, under water, of animals of different
species, and in animals of the same species, but of different ages and
exposed to various degrees of external temperature. See table on p. 746.

The importance of these observations lies in the fact that they con-
firm many of the results obtained by experiments upon the respiratory
exchange of different animals. Thus an examination of the above tables
shows that the small animals die more quickly than the big animals,
and it has been proved that weight for weight they have a more rapid
metabolism.* Further, a marked difference is observed in hens and
ducks, for the latter can live under water three or four times as long as
the former. The explanation of this fact is, according to Paul Bert,^ to
be found in the relatively greater quantity of blood in a duck. A
similar condition appears to obtain in the seal and whale ,^ which can
remain under water from fifteen to thirty minutes.

The tables also show that new-born animals born helpless and blind
resist submersion for a much longer time than adults, a fact known and
studied by Harvey,^ Haller,^ Buffbn,^ and Legallois,^'^ but the duration of

^ Bernard, quoted from Paul Bert, loc. cit. p. 522.

- '-'De rinfiuence des agens physiques sur la vie," Paris, 1824, pp. 629-632.
^ Loc. cit., p. 534.

^ This article, p. 720. See also "Animal Heat," this Text-book, vol. i. p. 852.
® Loc. cit., p. 550.

® Burdach, "Traits de physiologic, " trad, par Jourdan, tome vi. p. 122.
' "De Generatione," Amst., 1651. '^ "Elementa physiologiae," 1761, p. 316.

^ " Histoire naturelle de I'homme."
^^ " CEuvres de Legallois, " Paris, 1824, tome i. p. 93.



746



CHEMISTR Y OF RESPIRA TION.



life under water is much shortened when the temperature of the water is
high. The explanation of this is to be sought in the fact that the respi-
ratory exchange of these immature animals is relatively small, and rises
and falls with the external temperature.^



Animal.


Tempera-
ture of
Water.


Duration of
Life.


Remarks.


Observer.


Mammals —




Min.


Sec.






Dog ....




4


25


Mean of three experiments.


Paul Bert.


,, five days old





12


5


, , two , ,


Edwards.


J ) J 5


22 -"S


55


30




j^


Cat, two months old .




2


50




Paul'Bert.


,, two days old





4


33


,, nine ,,


Edwards.


)! J J


10"


10


23


, , three , ,


jj


5> ,,


20°


38


45


,, two ,,


,.


;> 51


26'^


34


30




) J


?? ))


30°


29





,, two ,,


5 )


) J ) >


42°


10


27


,, four ,,




Kitten, very young


14°


27


30




Paul'Bert.


!I ) >


20°


26







J,


>) >)


26°


18







^


J) ;;


36°


11


30




^^


Seal, 1 metre long




15-28







J J


Rabbit




3





Mean of six experiments ;
rabbits without food for
previous twenty - four
hours.




,, .




2


53


Mean of three experiments ;
rabbits well fed pre-
viously.


"


Guinea-pig .




2







))


, , adult




3


35


Mean of three experiments.


Edwards.


,, two to three




5


25


11 ■''i-'^ 11




days old












Birds—












Sparrow








30


Mean of seven experiments.


,,


5) ...


20°



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 104 of 147)