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the subject of much discussion and criticism between Pflliger ^ and
Voit.*5 It is impossible here to go fully into the causes of some of the
contradictory results, but Pflliger appears to have shown that the
variations in the breathing have no influence upon the respiratory
metabolism beyond this, that when the respiratory muscles are more
active, an extra amount of metabolism, due to this activity, will occur.
Pflliger takes the mean of the conflicting results and obtains the
following suggestive figures : — •

Carbon dioxide discharged in fifteen minutes —



Authority.


Five Respirations
per Minute.


Sixty Respirations
per Minute.


Lossen .
Berg .


7-96 grms.
7-712 ,,
15-672 ,,
Mean . 7-836 ,,


6-63 gi-ms.
9-106 ,,
15-736 ,,
Mean . 7-868 ,,



'^ Arcli. d. Ver.f. wissenscli. Heilk., Leipzig, 1867, Bd. iii. S. 317.

2 "Physiologic des menschlichen Athmeus," Leipzig, 1892 ; Arch. f. Physiol., Leipzig,
1896, S. 465.

^ Arch. f. d. ges. Physiol., Bonn, 1888, Bd. xliii. S. 523, et seq.

^ Hesse, Arch. f. Hyg., Miinchen u. Leipzig, 1884, Bd. ii. S. 381; "Physiol, d.
Athmens," Karlsruhe, 1845, S. 116, 134.

s Arch.f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 1, 630.

^ Ztschr. f. Biol., Miinchen, 1878, Bd. xiv. S. 95.



756 CHEMISTR Y OF RESPIRA TION.

This conclusion is supported by the work of Pflliger's pupils, Finkler and
Oertmann,^ who found that artificial respiration and apnoea^ produced no
alteration in the absorption of oxygen by rabbits. The respiratory exchange
is determined by the activity of the tissues, and not by the frequency of
respiration, or the amount of oxygen contained in the blood.

Other changes in the respired air. — It has been shown that in
a man at rest the air respired undergoes a reduction in oxygen to about
16 per cent., and an increase in carbon dioxide to about 4 per cent. ; in
addition, the temperature of the inspired air is raised to that of the
body, and this generally occurs before the air reaches the smaller
bronchi. At this temperature the air is saturated with moisture, and-
shows when dried a slight reduction, about -^''q in volume, when it is com-
pared with the inspired air, and both are measured at 0° and 760 mm.
This decrease in volume is due to the combination and retention of some
of the oxygen in the tissaes, to the oxidation of some substances which
leave the body otherwise than by the lungs, and to the combination of
oxygen with hydrogen to form water. The oxygen does not reappear
entirely as oxygen in combination with carbon to form carbon dioxide ;

this is shown by the respiratory quotient, yr-^, which in omnivorous and

carnivorous animals is about 0"8. The effect of diet and other con-
ditions upon the respiratory quotient is considered elsewhere in this
work, and it has been shown ^ that, under certain conditions, marsh-
gas, hydrogen, and nitrogen may be discharged by the lungs.

The Effect of Kespieation upon the Blood.

Historical. — -The discovery of Harvey that every portion of blood passes
through the lungs during each complete circulation, confirmed the idea of the
early physiologists, that respiration produced important changes in that fluid ;
Harvey ^ himself thought that the blood discharged some noxious substances
as well as aqueous vapour into the air of the lungs. ^

In 1669, Lower "^ observed, on opening the thorax of a living animal, and
keeping up artificial respiration, that the change of colour from venous to
arterial took place in the capillaries of the lungs ; the blood in the right
ventricle was dark, and if the artificial respiration ceased it passed through the
lungs to the left ventricle without attaining an arterial hue ; venous blood,
when exposed to air outside the body, acquired an arterial colour. Mayow,''^
even earlier than 1674, maintained that this change from venous to arterial
colour was due to the absorption by the blood of the nitro-aerial gas (oxygen)
from the air in the lungs, but his work was neglected and forgotten.

About the year 1776, Priestley ^ made a series of experiments, in which he
showed that dark blood clot became red more rapidly in oxygen than in air,
but the red colour was reduced to purple when the clot was placed in nitrogen,
hydrogen, or carbon dioxide ; these alterations in colour also took place when
the blood clot was separated from the air by a piece of moistened bladder, or
by a thin film of milk. These changes were supposed by Priestley to be

1 Arch.f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 38. See also Pfluger, ibid., S. 9.

"See also Haiiriot and Richet, Compt. rend. Acad. d. sc, Paris, 1887, tome civ. ji. 1327.

3 This article, pp. 700, 729,

* "De Motu Cordis."

•'' For older theories see p. 692, and the references there given.

" "Tractatus de Corde," Londini, 1669, pp. 175, 181.

■^ "Tractatus Primus," Oxon., 1674, p. 148.

8 Phil. Trans., London, 1776, pt. 1, p. 226.



GASES OF THE BLOOD. 757

similar to those of combustion, but, biassed by his belief in an old theory, he
concluded that the removal of " phlogiston " turned venous into arterial blood,
and for this purification respiration was necessary. For many years there
were two hypotheses to account for the effect of respiration on the blood.
According to the one, Avhich originated apparently with Black,^ and was
accepted by Priestley, Lavoisier,- and Crawford,'^ the oxygen in the inspired air
combined Avith the carbon in the venous blood of the lungs, and formed
carbon dioxide, which was discharged ; whereas, according to the other
hypothesis, proposed by Le Grange,^ the oxygen was absorbed by the blood,
and, during the course of the so-called systemic circulation, combined with
carbon to form carbon dioxide, which was liberated when the blood again
reached the lungs and took up a fresh supply of oxygen.

ISTotwithstanding the experiments of Spallanzani ^ and of Edwards,^
which proved that snails, frogs, and kittens continued to give out carbon
dioxide in an atmosphere of hydrogen, the view that oxidation took place
in the blood was held until recent times, when the work of Pfliiger and
his pupils showed conclusively that the tissues were the important seat of
combustion.

According to Bohr,'' the tissues of the lungs have a further function than
that of simply absorbing and discharging gases ; they are said to be able to
form carbon dioxide from substances brought to them from other parts of the
body. Thus Bohr and Henriques ^ found that the lungs supplied 68 per cent,
of the respiratory metabolism. It must be pointed out that in many of the
experiments upon which this conclusion is based, the operative procedure was
exceedingly severe, and the condition had no approximation to the normal ;
further, the results are not supported, in fact are contradicted, by the
numerous experiments on internal respiration.

The effect of respiration upon the blood is best studied by a com-
parison of the gases containecl in venous blood taken from the right
ventricle, and in arterial blood taken from the carotid artery.

The gases of the blood. — Methods for the extraction and esti-
mation of the gases of the blood. — Historical. — The first demonstration
of the presence of gases in the blood was made by Boyle ^ in 1636; he
showed that, when fresh defibrinated blood was exposed to the vacuum of
an air-pump, gas was given off. These particles of gas Mayow,i° in 1674,
considered to be nitro-aerial gas, that is, oxygen. The next important observa-
tion was that made by Priestley,!^ who noticed that blood placed in an
atmosphere of hydrogen or nitrogen gave off oxygen. Girtanner ^^ observed
the same effect with nitrogen. In 1799, Humphry Davy ^^ found that
twelve volumes of arterial blood, when heated to 93°, gave off 1*1 volume of
carbon dioxide, and 0"7 volume of oxygen.

Nasse,^"* in 1816, proved that blood gave up oxygen to an atmosphere of

^ " Lectures on Chemistry," edit, by Eobison, Edinburgh, 1803.
"Hist. Acad. roy. d. sc, Paris, 1777, 1789, 1790.
•* " On Animal Heat," 2nd edition, 1788.
■* Hassenfratz, Ann. de chim., Paris, 1791, tome ix. p. 275.
° "Mem. sur la respiration," trad, par Senebier, 1803.
^ " De I'influence des agens physiques sur la vie," Paris, 1824.
■^ Skandin. Arch. f. Physiol., Leipzig, 1891, Bd. ii. S. 236.

** CentralU. f. Physiol., Leipzig u. Wien, 1892, S. 22.5 ; Commit, rend. Acad. d. sc,
Paris, 1892, tome cxiv. p. 1496.

^ "Nova experimenta pueumatica respirationem spectantia," Geneva, 1636.
" "Tractatus quinque," Oxonii, 1674. "Opera omnia," Hagae Com., 1681, p. 133.
11 Phil. Trans., London, 1776, pt. 1, p. 226.
1^ Hassenfratz, Ann. de chim., Paris, 1791, tome ix. p. 275.
13 Ann. d. Phys. u. Chcm., Leipzig, 1803, Bd. xii. S. 574, 593.
'^^ Deutsches Arch. f. d. Physiol., Halle, 1816, Bd. ii. S. 195, 435.



758



CHEMISTR Y OF RESPIRATION.



hydrogen, or of carbon dioxide, and Vogel,^ in 1814, and Collard de Martigny,"
in 1830, obtained carbon dioxide, but no oxygen, from blood subjected to a
vacuum. ISTotwitlistanding these observations, the presence of gases in the
blood was for a long time a subject of controversy. Many physiologists,
among them Johannes Muller,^ Schroeder van der Kolk,'^ Gmelin,^ Mit-
scherlich,^ and Tiedemann,^ maintained that no gas existed in the blood,
whereas I^asse,*' Scudamore,^ Bischoff,^ and Van Euschut ^ obtained from
blood carbon dioxide, but no oxygen. John Davy was at first ^'^ unable to

extract any gas from
blood, but during a
further research he
obtained carbon dioxide
from both arterial and
venous blood.^^

More exact methods
of observation were in-
troduced in 1837 by
Magnus, 12 who adopted
and improved, for the
extraction of the gases,
the use of a Torricellian
vacuum, a method due
originally to Collard de
Martigny. The conclu-
sions to which Magnus
arrived were that blood
contained 4-8 volumes
per cent, carbon dioxide,
1-3 -5 volumes per cent,
oxygen, and 0*5-2
volumes per cent, nitro-
gen, and that arterial
blood contained more
oxygen than did venous
blood. rernet,i3inl857,
published the results of
experiments in which he
had extracted the gases
of the blood by the
passage of a stream of
hydrogen, and the aid
of a vacuum. About
the same time, Lothar Meyer ^^ developed the method ^^ of heating the blood
or other liquid for the extraction of its gases, and a still further advance was

^Journ. f. Chem. u. Phys., Niirnberg, 1814, Bd. xi. S. 399.

~ Journ. dafliysiol. exjoer., Paris, 1830, tome x. p. 111.

2 " Handbucli d. Physiol.," Bd. i. S. 315.

"* " Dissertatio sistens sanguinis coagulantis historian!."

5 Ztschr. f. Physiol., 1833, Bd. v. S. 6.

^ Loc. cit.

"• "An Essay on the Blood," London, 1824.

** " Commentatio, etc.," Heidelbergfe, 1837.

" "De respirationis Chyniisnio," Trajecti ad Ehennni, 183G. pp. 78, 84, 98, 115, 142.

^^^P/ii^. Tj-aiis., London, 1823, p. 516.

" "Re.searches," London, 1839, voh ii. p. 156, et seq.

^'^ Ann. d. Phys. u. Chem., Leipzig, 1837, Bd. xl. S. 583 ; 1845, Bd. Ixvi. S. 177.

'•'Ann. d. sc. nal., Paris, 1857, S6'. 4, ZooL, tome viii. p. 125.

1^^ "Die Gase des Blutes," Gottingen, 1857 : Ztschr. f. rat. Med., N.F., Bd. viii. S. 256.

15 Used originally by H. Davy, Bunsen, and Bauniert.




Fig. 69.— Pfliiger's Pump; a, blood bulb; h, froth-chamber;
d, drying tube ; e, mercurial gauge ; h, graduated tube
for collection of gas ; I, m, n, and o, bulbs and tubing
containing mercury.



GASES OF THE BLOOD.



759



made when Ludwig and Setschenow/ Pfliiger ^ and Helmholtz,^ constructed
their mercurial gas-pumps, based upon the principle of the Torricellian vacuum.

The mercurial gas-pump. — Numerous forms'^ of this apparatus have been
introduced, but here it is only necessary to mention Pfliiger's pump, the
modification of this made by Gr^hant,^ and the, simple apparatus devised by
Leonard Hill. The principle of the first is shown in the diagram on p. 758.

Further details upon the construction and. working of these pumps will
be found in text-books of physiological chemistry. "^

In Leonard Hill's '' gas-pump, the chief advantages are simplicity, cheap-
ness, and rapidity of action ;
the working errors are under
1 per cent., and only small
quantities of blood are required.
The construction of the pump
is shown in Fig. 70, and
the successive manipulations
are as follows : — " A blood-
receiver (F) is affixed to the
end of the tube E, and the
receiver is elevated into the
position indicated by the dotted
outline. The reservoir (B) is
then put in connection with
the tube (E) by means of the
three-way tap (D), the reservoir
(A) is raised above the pump,
and the whole system is filled
with mercury to the top of the
blood-receiver (F). The screw-
clip on the rubber tube at the
upper end of F is then closed,
and the reservoir (A) lowered
until the blood-receiver is ex-
hausted, except for 2 or 3 c.c.
of mercury, which is purposely
left within. The screw-clip on
the lower end of F is next closed,
and the blood-receiver now
clipped at either end, exhausted,
detached froaxi tube E, and
weighed. A sample of blood is
then collected. The arterial or
venous cannula is filled with
blood, and immediately afterwards

'^ Sitzungsh. d. Tc. Akad. d. Wissensch. iMath-phys. CL, Wien, 1859, Bd. xxxvi. S. 293.

2 " Untei-such. a. d. Bonner physiol. Lab.," 1865, S. 188; CentralM. f. d. med.
Wissenftch., Berlin, 1866, S. 305 ; Arch. f. d. ges. Physiol., Bonn, 1868, Bd. i. S. 61.

3 See Zuntz, Hermann's "Handbuch," Bd. iv. Th. 2, S. 27.

^A. Schmidt, Ber. d. k. sdchs. GeseUsch. d. Wissensch. Math-phys. CI., Leipzig, 1867,
Bd. xix. S. 33 ; Hoppe-Seyler, "Physiol. Chem.," Berlin, 1879, Bd. ill. S. 491 ; Nawrocki,
Stud. d. physiol. Inst, zu Breslau, Leipzig, Bd. ii. S. 144 ; Buseh, Arch. f. d. ges. Physiol.,
Bonn, 1869, Bd. ii. S. 445 ; Kossel and Raps, Arch. f. Physiol., Leipzig, 1893, S. 198.

5 Paul Bert, " Lecons sur la physiol. comp. de la respiration," Paris, 1870, p. 102;
"La pression baromi^trique," Paris, 1878, p. 615.

8 Halliburton, "Text-Book of Chemical Physiology and Pathology," London, 1891, p.
30; Hempel, " Gasanalytische Methoden;" Gaingee, "Physiological Chemistry of the
Animal Body," vol. i. pp. 200-206.

^ Journ. Physiol., Cambridge and London, 1894-5, vol. xvii. p. 353; Hill and Nabarro,
ibid., 1895, vol. xviii. p. 218.




Pig. 70. — Leonard Hill's Gas-Pump,
pushed into the ru.bber tube at the



76o CHEMISTR Y OF RESPIRA TION.

end of the blood-receiver, as far as the closed screw-clip. Before the
insertion of the cannula, the end of the rubber tube is compressed with
the fingers to exclude the air withm it. A sufficient quantity of blood
is now withdrawn by opening at the same time the screw-clip and the
clip placed on the blood vessel of the animal. The blood is defibrinated
by shaking it with the mercury left Avithin the blood-receiver for that
purpose, and the latter is then again weighed. The weight of the sample
of blood is then obtained. The blood-receiver is next affixed once more to the
tube (E), in the dependent position shown in the figure, and the tube (E) is
exhausted. Finally, the screw-clip between E and the blood-receiver is
opened, and the gases are withdrawn and collected in the eudiometer. Since
the blood-receiver hangs freely from the tube (E) by means of a piece of
rubber tubing, it can be both immersed in warm water, and .shaken to facilitate
the complete escape of the gases. The bulbous form of the blood-receiver
prevents the blood from frothing over into the pump ; and if the action
becomes too violent, it can be immediately allayed by pouring a few drops
of warm water on to the tube (E). The bubbles are thereby driven back into
the receiver, and the pump is never fouled. The tap (D) is so manipulated
that the gases only, and not the water which condenses in the reservoir (B),
are driven over into the eudiometer. The water is returned back into the
blood-receiver. Three or four exhaustions are sufficient to extract all the gases
from about 10 grms. of blood."

Methods of gas analysis cannot be described here ; it is only necessary to refer
the reader to the works of Bunsen, Hempel, and others^ upon this special subject.

In the extraction of the gases of the blood methods are employed which
favour the dissociation of those gases which are present in loose chemical
combination, and also liberate the gases present in a state of simple solution.
These conditions are fulfilled by exposure to a vacuum, by warming and
agitating the blood. The addition of a weak acid favours the evolution of the
carbon dioxide. The effect of these different procedures upon the dissociation
of oxyhaemoglobin will be considered later ; here it is only necessary to recall
the fact that the coefficient of absorption of gases in fluids diminishes with an
increase of temperature, and becomes nil when the boiling point of the fluid is
reached.

For the quantitative estimation of the oxygen contained in blood, Claude
Bernard 2 introduced a method based upon the stronger affinity shown by
carbon monoxide than by oxygen for hajmoglobin. The blood is shaken with
double its volume of carbon monoxide, which drives out the oxygen from its
combination with hsemoglobin. An analysis of the gas collected shows the
percentage of oxygen. Nawrocki ^ has made comparative analyses with this
method and with the ordinary blood pump, and the results are practically the
same. If, hoAvever, the blood is left in contact with the carbon monoxide for
longer than twenty-four hours, some of the gas combines with oxygen to form
carbon dioxide, and thus the amount of oxygen is diminished. * It is possible
that the carbon dioxide formed in these cases is due to putrefaction.

The diflferences in the gases of arterial and venous blood. —
A comparative examination of the gases contained in arterial and venous
blood is necessary for the estimation of the qualitative and quantitative
changes which occur during external and internal respiration.

The gases of arterial blood. — The chief results obtained by

^Bunsen, " Gasometrische Metlioden," 1857; "Gasometry," Roscoe's transL, London,
1857; cf. also Gamgee, oj). cit., pp. 206-215; Hempel, " Gasanalytische Metlioden";
Geppert, " Die Gasanalyse," 1885.

^ " Le9ons sur les liquides de I'organisnie," Paris, 1859, tome i. p. 365 ; ii. p. 427.

^ Stud. d. physiol. Inst, zu Breslau, Leipzig, Bd. ii. S. 144.

■* Bernard, loc. cit., Pokrowsky, VircJioiv's Archiv, 1866, Bd. xxxvi. S. 482.



GASES OF ARTERIAL BLOOD.



761



different observers upon various animals have been collected in tabular
form by Zuntz/ and are here reproduced with some additions : —









Quantity


of Gas in Percentage










of Volume of Blood,










Measured at 0° and


760 Mm.


Observer and Number of


Animal.












Experiments.


Oxygen.


Nitrogen.


Carbon
Dioxide.


Dog .




Mean


22-6


1-8


34-3


Pfiliger,^ twelve experiments, but
only three determinations of
CO2. Rapid method employed.




f
'1


Mean


18-3


1-8


37-7


Forty-four analyses of carotid


Dog .


Max.


24-7


5-5


53-4


blood by Setschenow, Schceffer,




Min.


11-4


1-2


23-3


Sczelkow, Nawrocki, Hirsch-














mann, Sachs and Pfiiiger. Col-














lected by Pfiiiger.^


Dog .




Mean


18-4


2-0


38-8


Blood of femoral artery. Twenty-
five analyses by Pfiiiger,^ two
by Hirschmann.




{


Mean


19-4




40-4


One hundred experiments by Paul


Dog .


■1


Max.

Min.


26-4
14-4




50-8
33-0


Bert.-*


Dog .






17-58




38-57


Geppert and Zuntz.^




./




15-4


1-5


40-1


Grehant."


Dog .




21-2


1-5


45-9




,




15-2


1-8


40-0








22-7


1-5


40-4






■\




17-3




33-4


Ewa Id. 7


Dog .




15-4
15-8




32-4
35-1








15-7




26-35




Dog .




Mean


18-25




37-64


Hill and Nabarro,® average of
fifty -two samples of arterial
blood.


Cat .




Mean


13-1


1-3


28-8


P. Heriiig,^ six experiments. The
vah;e of oxygen is too Ioav,
since phosphoric acid was
added to the blood beforehand.


Sheep .




Mean


10-7


1-8


45-1


Sczelkow.^" Two analyses.


Sheep .




Mean


12-8






Three analyses by Preyer " on
venous blood shaken with air.


Rabbit




Mean


13-2


2-1


34-0


Four analyses by Walter, ^"


Rabbit






10-9




37-34


Geppert and Zuntz.^^


Man .






21-6


1-5


40-3


One analysis by Setschenow.



^ Article in Hermann's "Handbuch," Bd. iv. Th. 2, S. 35.

^ Gentralhl. f. d. ined. JFissensch., Berlin, 1867, S. 722.

3 Arch.f. d. gcs. Physiol., Bonn, 1868, Bd. i. S. 274.

■* "La pression barom(5trique," Paris, 1878, p. 1030.

® Arch.f. d. ges. Physiol., Bonn, Bd. xlii. S. 189.

^ Compt. rend. Soc. de biol., Paris, 1892, p. 163.

''Arch.f. d. ges. Physiol., Bonn, 1873, Bd. vii. S. 575.

* Journ. Physiol., Cambridge and London, 1895, vol. xviii. pp. 223, 224, 227.

^ " Untersuch. u. d. Zusammensetzung der I31utgase wahrend der Apuoe," Diss.
Dorpat, 1867, Meissncr's Jahresb., 1867, S. 305.

^"Arch.f. Anat., Physiol, u. wissensch. Med., 1864, S. 516.
" JVien. mecl. Jahrh., 1865, S. 145.

'^'^ Arch. f. ex2Kr. Path. u. Pharmakol., Leipzig, Bd, vii. S. 148,
^^ Arch.f. d. ges. Physiol., Bonn, Bd. xlii. S. 189,



762 CHEMISTRY OF RESPIRA TION.

Tlie results of analyses of the gases iii the blood of birds and of other
animals are given by Zuntz.^

Estor and Saint-Pierre ^ concluded, from a few analyses of arterial blood,
that the amount of oxygen diminished in proportion to the distance of the
artery from the heart ; these results, however, have been shown by Paul Bert,^
Hirschmann,* and Pfliiger ^ to be erroneous. The blood in the smaller arteries
contains less oxygen, but this is independent of the distance from the heart,
and appears to be due to the smaller number of red corpuscles, and the
loAver specific gravity of the blood. "^

The results given in the above table show considerable diiferences in the
percentage composition of the gases of arterial blood, even when the experi-
ments have been made upon similar animals. The causes of these differences
are partly due to variations in the gases in the blood, and partly to errors of
analysis. In order to test these points, double analyses of portions of the same
blood have been made by Preyer and Ludwig,'^ Pfliiger,^ and others. ^ The
most important discovery in this connection is that made by Pfliiger ; ^^ the
ordinary methods for the extraction of the gases of the blood give results
which for the oxygen are too low, for the carbon dioxide too high ; arterial
blood, when removed from the body, and kept from contact with the air,
rapidly becomes darker. Some of the oxygen appears to be used up by the
corpuscles with the production of carbon dioxide. If the blood be received
directly from the artery into a large vacuum, and the gases quickly extracted,
then values are obtained which show a higher percentage of oxygen, and a
lower percentage of carbon dioxide than those found by the ordinary slower
methods. The normal amount of oxygen in the fresh arterial blood of the
dog is about 22 per cent. The carbon dioxide naturally shows considerable
variations, but the amount of nitrogen in the most exact determinations is
fairly constant, about 1'8 per cent.

The arterial blood is not quite saturated with oxygen, for by rapid
artificial respiration in the living animal, or by shaking arterial blood
with air, the amount can be raised above 23 volumes per cent.^^ Geppert
and Zuntz found in the arterial blood of dogs a relative saturation with
oxygen of 96-99 per cent.^^ The quantity of carbon dioxide in arterial
blood is only about one-fifth of the amount which can be held by the
blood, for Paul Bert^^ found that dog's blood could take up about 150
volumes per cent, when shaken with pure carbon dioxide. The nitrogen
is simply in solution and the blood appears to be saturated with that
gas, for the ordinary pressure and temperature.

The gases of venous blood. — On account of the differences in the
metabolism of the different tissues of the body, the venous blood is liable

^ Article in Hermann's " Handbuch," Bd. iv. Th. 2, S. 41.
- Journ. de Vanat. et x>hysiol. etc., Paris, 1865, tome ii. p. 302.
■* " Lemons sur la j^hysiol. comp. de la respiration," Paris, 1870, p. 118.
^ Arch. f. Aiiat., Physiol, u. wissensch. Med., 1866, S. 502.
s Arch./, d. ges. Phyniol., Bonn, 1868, Bd. 1. S. 274.

^ Matliieu and Urbain, Arch, de physiol. norm. etx>ath., Paris, 1871, tome iv. ; Pfliiger,



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