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point, namely, immediately below the origin of the first branches which are given off
from the bronchial trunks. The combined sectional area is here no greater than the
sectional area at the lower end of the trachea, although the combined area of the
undivided bronchi is distinctly greater than this. (C. Aeby, Der Bronchialbaum
der Saugethiere und des Menschen, Leipzig, 1880.)

Dimensions of the lungs. The lungs vary much in weight according to the
quantity of blood they may happen to contain, as well as from other causes.
The weight of both lungs together, as generally stated, ranges from 30 to 48 ounces,
the more prevalent weights being found between 36 and 42 ounces (1,300 grammes
in the male and 1,023 grammes in the female, according to W. Krause). The
proportion borne by the right lung to the left is nearly that of 22 ounces to 20,
taking the combined weight of the two at 42 ounces (682 to 618 grammes, taking
the combined weight as 1,300). The lungs are not only absolutely heavier in the
male than in the female, but appear to be heavier in proportion to the weight of the

Their extreme length in the male is 271 mm. for the right and 298 mm. for the
left lung ; in the female 216 mm. and 230 mm. respectively. The extreme outer
and posterior diameters of the right and left lungs respectively are in the male
203 mm. and 176 mm., and in the female 176 mm. and 162 mm. The transverse
diameter at the base is in the male 135 mm. (right) and 129 mm. (left), and in the
female 122 mm. (right) and 108 mm. (left). These numbers are also taken from
Krause (quoted by Vierordt).

Physical properties. The substance of the lung is of a light porous spongy
texture, and, when healthy, is buoyant in water : but in the foetus, before respira-
tion has taken place, and also in certain cases of congestion, collapse, or consolida-
tion from disease, the entire lungs, or portions of them, sink in that fluid. The
specific gravity of a healthy lung, as found after death, varies from 0*345 to 0'746.
When the lung is fully distended its specific gravity is 0*126, whilst that of the
pulmonary substance, entirely deprived of air, is T056 (Krause). When pressed
between the fingers, the lungs impart a crepitant sensation, which is accompanied by
a peculiar noise, both effects being caused by the air contained in the tissue. On
cutting into the lung, the same crepitation is heard, and there exudes from the cut
surface a reddish frothy fluid, which is partly mucus from the air-tubes and air-
cells, and partly serum of blood, rendered frothy by the admixed air.

The pulmonary tissue is endowed with great elasticity, in consequence of which
the lungs collapse to about one-third of their bulk when the thorax is opened.
Owing to this elasticity also, the lungs, if artificially inflated out of the body,
contract to their previous volume when the air is again allowed to escape.

In infancy the lungs are of a pale rose-pink colour, which might be compared to
blood-froth ; but as life advances they become darker, and are mottled or variegated
with spots, patches, and streaks of dark slate-colour, which sometimes increase to
such a degree as to render the surface almost uniformly black.

The dark colouring-matter found in these streaks is in the form of granules and collec-
tions of granules, frequently not enclosed in cells ; it is deposited in the interstitial areolar
tissue mostly near the surface of the lung, and is not found so abundantly in the deeper
substance. It exists sometimes in the air-cells, and on the coats of the larger vessels. Its
quantity increases with age, and is said to be less abundant in females than in males. In
persons who follow the occupation of miners, more especially colliers, the lungs are often
intensely charged with black matter. The black substance seems mainly to consist of
particles of carbonaceous substance. It is found also in the bronchial glands ; indeed, it.


appears to be taken up in large measure by the lymphatics. In exceptional cases the adult
lungs exhibit only very slight streaks of pigment.

Condition in the foetus and changes after birth. In the foetus the lungs
contain no air, and consequently sink in water. They undergo very rapid and
remarkable changes after birth, in consequence of the commencement of respiration :
these affect their size, position, form, consistence, texture, colour, and weight, and
should be carefully studied, as furnishing the only means of distinguishing between
a still-born child and one that has respired.

1. Position, size, and form. In a foetus at the full period, or in a still-born
child, the lungs, comparatively small, lie packed at the back of the thorax, and do
not entirely cover the sides of the pericardium ; subsequently to respiration they
expand, and completely cover the pleural portions of that sac, and are also in contact
with almost the whole extent of the thoracic wall, where it is covered with the
pleural membrane. At the same time their previously thin sharp margins become
more obtuse, and their whole form is less compressed.

2. Consistence, texture, and colour. The introduction of air and of an increased
quantity of blood into the foetal lungs, which ensues immediately upon birth,
converts their tissue from a compact, heavy, granular, yellowish-pink, gland-like
substance, into a loose, light, rose-pink, spongy structure, which, as already
mentioned, floats in water. The changes thus simultaneously produced in their
consistence, colour, and texture, occur first at their anterior borders, and proceed
backwards through the lungs : they, moreover, appear in the right lung a little
sooner than in the left.

3. Weight. The absolute weight of the lungs having gradually increased from
the earliest period of development to birth, undergoes at that time, from the quantity
of blood then poured into them, a very marked addition, amounting to more than
one-third of their previous weight : for example, the lungs before birth weigh about
one ounce and a half, but after complete expansion by respiration they weigh as
much as two and a half ounces. The relative iveight of the lungs to the body,
which at the termination of intra-uterine life is about 1 to 70, becomes, after
respiration, on an average about 1 to 35 or 40 ; a proportion which is not materially
altered through life. The specific gravity is at the same time changed from T056 to
about '342.


Termination of the bronchi; structure of the bronchial tubes. The

principal divisions of the bronchi, as they pass into the lungs, divide into tubes of
less calibre, and these again subdivide in succession into smaller and smaller tubes,
often distinguished as bronchia, bronchioles, or bronchial tubes, which, diverging in
all directions, never anastomose, but terminate separately. The larger branches
diverge at acute angles, but the more remote and smaller ramifications spring less
acutely. After a certain stage of subdivision each bronchial tube, reduced to a small
size (about 0'2 mm.), is termed a tabular or respiratory bronchiole (Kolliker), and
its walls become beset with small hemispherical saccules, termed air-cells, or alveoli.
They occur at first only here and there, and confined to one side of the tube only,
but at length almost cover it, so that the tube in great measure loses its cylindrical
character. At length it ends in an enlarged completely sacculated passage, termed
the alveolar passage (atrium, Miller), from which are given off blind ramifications,
somewhat enlarged towards their extremities, and everywhere closely beset with the
air-cells. These enlarged terminations, or ultimate lobules, which measure about
1 mm. in diameter, are named infundibula (fig. 200).

Within the lungs the air-tubes are not flattened behind like the bronchi and
trachea, but form completely cylindrical tubes. Hence, although they contain the



same elements as the larger air-passages, they are reduced gradually to a state of
greater tenuity, but possess certain peculiarities of structure. Thus, the cartilages
no longer appear as imperfect rings running only upon the front and lateral surfaces
of the air-tube, but are disposed over all sides of the tubes in the form of irregularly



a, cartilage and fibrous layer with mucous glands, and, in the outer part, a little fat ; in the
middle, the duct of a gland opens on the inner surface of the tube ; I, annular layer of involuntary
muscular fibres ; c, elastic layer, the elastic fibres in bundles which are seen cut across ; d, columnar
ciliated epithelium.

shaped plates and incomplete rings of various sizes. These are most developed at
the points of division of the bronchia, where they form a sharp concave ridge
projecting inwards into the tube. They may be traced, becoming rarer and rarer
and more reduced in size, as far as bronchia one millimeter in diameter. The fibrous

d. c b a

(F. E. Schultze). MAGNIFIED 240 DIAMETERS.

a, fibrous layer ; 6, muscular layer ; c, mucous membrane in longitudinal folds, with numerous
longitudinally running elastic fibres cut across ; d, ciliated epithelium ; /, surrounding alveoli.

coat extends to the smallest tubes, becoming thinner by degrees, and degenerating
into areolar tissue. In it are mucous glands which send their ducts to open on the
mucous membrane. These occur most numerously in the larger tubes ; in those
which measure less than 1 mm. they are rarely if ever found. The mucous membrane,
which extends throughout the whole system of air-passages, is also thinner than in



the trachea and bronchus, but it retains its ciliated columnar epithelium (figs. 198,
199, d). The longitudinal bundles of elastic fibres (c, in the transverse sections) are
very distinct in both the large and small bronchia, and may be followed by dissection
as far as the tube can be laid open, and by the microscope into the smallest tubes.




B, bronchial tube ; L.B., lobular bron-
chiole ; A, atrium ; i, infundibulum ; C,

The muscular fibres, which in the

trachea and bronchi are confined to

the back part of the tube, surround

the bronchial tubes with a continuous

layer of annular fibres, lying inside

the cartilaginous plates (&) ; they

are found, however, beyond the

place where the cartilages cease to exist, and appear as irregular annular fasciculi

even in the smallest tubes.

Pulmonary alveoli. At the point where the small bronchial tubes lose their
cylindrical character, and begin to be beset with air-cells, their structure also
gradually undergoes a change. The muscular layer almost disappears, the longitu-



The small granular and the large flattened cells of the alveoli are shown. In the middle is a section
of a lobular bronchial tube, with a patch of the granular pavement epithelium-cells on one side.

dinal elastic bundles are broken up into an interlacement of elastic tissue, which
surrounds the mouths of the air-cells and the walls of the infundibula, and
the columnar ciliated epithelium gives place to a stratum of non-ciliated cells. The
change in the character of the epithelium first occurs in the lobular bronchioles,
where patches of small pavement epithelium-cells begin to appear amongst the



ciliated cells, especially in the neighbourhood of the air-cells upon the walls of these
tubes. At the end of the lobular bronchiole, near the passage to the infundibula,
all the cells which line the wall of the tube are of the non-ciliated pavement variety.
But the air-cells themselves, both those which are scattered over the respiratory
bronchioles and those which cover the infundibula, as well as intermediate portions
of the infundibula which occur here and there between the air-cells, possess an
epithelium of a peculiar character. The cells of this epithelium are of two kinds,
viz. : 1, large, thin, very delicate cells, irregular in size and shape, lying over the
blood-vessels, but also in many cases extending over the interstices between them ;
and, 2, small, flat, polygonal, nucleated cells, which lie singly or in small groups
of two or three cells, between the others, and always in the interstices of the capillary
network. These are similar to the cells which are found in patches in the lobular
bronchioles. If the lung is greatly distended they also become flattened out.

In the foetus the alveoli are entirely lined with small granular pavement cells, but with
the distension which follows upon the first respiratory efforts most of the cells become trans-
formed into the large thin epithelial elements above described.

The walls of the alveoli, which mainly consist of an indistinctly fibrillated
connective tissue, with corpuscles scattered here and there, are supported and

OP THE cow's LUNG (from Kolliker, after

a, pulmonary vesicles filled artificially
I, with wax ; b, the margins of the smallest
lobules or infundibula.

/, strengthened by scattered and coiled
elastic fibres, especially numerous
near their orifices, in addition to
which, according to some authori-
ties, there is likewise an intermixture
of muscular fibre-cells. A number
of leucocytes, mostly granular and
eosinophil, are usually to be found

free in the air-cells and smaller bronchial tubes : not unfrequently they contain
carbonaceous particles. By the migration of these cells into the pulmonary tissue,
the carbon particles may be conveyed into the substance of the lung and thence
into the lymphatics and bronchial glands.

The air-cells in the natural state are always filled with air. They are readily
seen on the surface and in a section of a lung which has been inflated with air and
dried ; also upon portions of foetal or adult lung injected with mercury or wax
(fig. 202, a, a). In the lungs of some animals, as of the lion, cat, and dog, they are
very large, and are distinctly visible on the surface of the organ. In the adult
human lung their most common diameter is about 0'25 mm. (-j^ inch), but it varies
from O'l mm. to 0'4 mm. ; they are larger on the surface than in the interior, and
largest towards the thin edges of the organ : they are also very large at the apex of
the lung. Their dimensions go on increasing from birth to old age, and they
are larger in men than in women. In the infant the diameter is usually under
0-12 mm.

The whole lung has a lobulated structure best seen in the foetus, where the lungs,
not yet distended with air, present very much the appearance of compound race-
mose glands. The infundibula may be regarded as corresponding to the smallest or
ultimate lobules of such a gland. They produce the appearance of polygonal areas
enclosing groups of six or eight air-cells which are seen at the surface of the lung


(fig. 202). The infundibula are grouped into larger or secondary lobules, and these
again into yet larger divisions. The various lobules are united and separated by
connective tissue in variable amount, more between the larger and less between the
smaller groups. From the mutual compression to which they are subjected the
lobules are bounded by flattened sides, and they are compactly fitted to each other
and to the larger air-tubes and vessels of the lungs.

Blood-vessels, lymphatics, and nerves of the lungs. Pulmonary
vessels. The branches of the pulmonary artery accompany the bronchial tubes,
but in their remote ramifications they subdivide more frequently. The main arterial
trunk runs down immediately behind the main bronchial trunk, giving off corre-
sponding branches as it proceeds. They ramify without anastomoses, and at length
terminate in small arteries about 0'025 mm. ( T oW inch) in diameter, which lie
between the alveoli, partially encircling their mouths (fig. 203, >). From these



a, a, free edges of alveoli ; c, c, partitions between neighbouring alveoli, seen in section ; 6, small
arterial branch giving off capillaries to the alveoli. The looping of the vessels to either side of the
partitions is well exhibited. Between the capillaries is seen the homogeneous alveolar wall with nuclei of
connective tissue corpuscles, and elastic fibres.

vessels the capillary network arises, and covers each alveolus, passing in the inter-
alveolar septa between the adjacent air-cells. As was pointed out by Rainey, the
capillary network in these partitions is single in the lungs of man and mammalia,
the capillaries winding through the septa from one alveolus to the other, although
in the lungs of amphibia and reptiles the capillary network of each alveolus is

The capillaries are fine, and the network they form so close that the meshes are
scarcely wider than the vessels themselves. They are very superficial, being covered
only by the thin layer of tesselated epithelium above mentioned, and in the parti-
tions between contiguous alveoli the vessels of the network project on either side in
an arched or loop-like manner into the cavities of the alveoli (fig. 203). The
mucous membrane of the bronchial tubes, especially near the air-cells, is partly
supplied with blood from branches of the pulmonary artery.


The radicles of the pulmonary veins arise from the capillary network of the
alveoli and from that of the smaller bronchial tubes. Their radicles are collected in
the septa between the infundibula, apart from the terminations of the arteries and
bronchioles. The branches of these veins which arise from the infundibula near
the surface of the lung run alone for a certain distance through the substance of
the organ. They finally either join some deeper vein which is passing towards the
hilum, or they remain superficial, forming a wide-meshed plexus near the surface
of the lung, finally tending towards the hilum to join the larger veins near the root
of the lung. The veins from the more deeply lying infundibula form frequent
communications, and finally coalesce into large branches, which ultimately accom-
pany the bronchial tubes and arteries, coursing as a rule in front of the bronchial
tubes, and thus proceed to the root of the lung. In their course together through
the lung the artery is usually found above and behind a bronchial tube, and the vein
below and in front.

The pulmonary vessels differ from the systemic in regard to their contents,
inasmuch as the arteries convey dark blood, whilst the veins carry red blood. The
pulmonary veins, unlike the other veins of the body, are not more capacious than
their corresponding arteries ; indeed, according to Winslow, Santorini, Haller, and
others, they are somewhat less so. These veins have no valves. The arteries of
different secondary lobules are usually independent, the veins freely anastomose.

Bronchial vessels. The bronchial arteries and veins, which are much smaller
than the pulmonary vessels, carry blood for the nutrition of the lung. The
bronchial arteries, from one to three in number for each lung, arise from the aorta ,
or from an intercostal artery, and follow the divisions of the air-tubes through the
lung. They are ultimately distributed in three ways : (1) many of their branches
ramify in the bronchial lymphatic glands, the coats of the large blood-vessels, and
in the walls of the bronchial tubes, supplying an outer capillary plexus with trans-
verse meshes to the muscular coat, and an inner plexus with close longitudinal
meshes to the mucous membrane, which in the lobular bronchioles is continuous
with that supplied by the pulmonary artery ; (2) others form plexuses in the inter-
lobular areolar tissue ; (3) branches spread out upon the surface of the lung
beneath the pleura, forming plexuses and a capillary network.

The bronchial veins have not quite so extensive a distribution in the lung as
the bronchial arteries, since part of the blood carried by the bronchial arteries is
returned by the pulmonary veins. The superficial and deep bronchial veins unite at
the root of the lung, opening on the right side into the large azygos, and on the left
usually into the left upper azygos vein.

According to Zuckerkandl it is not only at the extremities of the bronchial tubes that the
blood brought by the bronchial arteries is returned by the pulmonary veins, but in other parts
small bronchial veins open into pulmonary branches ; and even veins which receive branches
from the larger bronchia, from the bronchial glands, and from the posterior surface of the
pericardium, empty their contents partly into the great trunks of the pulmonary veins.

A few small branches of the 'intercostal arteries also pass to the pulmonary pleura and
surface of the lung through the ligamentum latum pulmonis (Turner).

Lymphatics. The alveolar lymphatics of the lung take origin from lymphatic
capillaries in the interalveolar septa, and those near the surface of the lung come into
connection with the subpleural lymphatic plexus, previously mentioned (p. 174).
They join to form vessels which accompany the branches of the pulmonary artery
and vein, running on the walls of those vessels in twos or threes, connected by
numerous cross branches, and in some cases almost completely surrounding the

Other lymphatics, which may be distinguished as bronchial, originate in
plexuses in the mucous membrane of the bronchial tubes. Hence they pass


through the muscular coat to form another plexus in the fibrous layer, where they
are most numerous on the side opposite the accompanying branch of_the pulmonary
artery. Here they are not unfrequently found to enclose nodules of lymphoid tissue.
The branched connective tissue corpuscles and cell-spaces with which the lymphatics
are in connection at their origin, send processes upwards to the inner surface of the
air tubes and alveoli, between the epithelial cells (like the pseudostomata of the
serous membranes). Lymphoid tissue is found, according to Arnold, in various
parts, viz., under the pulmonary pleura ; in the perivascular and peribronchial
tissue ; in the bronchial wall, and around the alveolar passages.

At the root of the lung the superficial and deep lymphatics unite into a few
anastomosing trunks before entering the bronchial lymphatic glands.

Nerves. -The nerves of the lung come from the anterior and posterior pul-
monary plexuses, which are formed chiefly by branches from the pneumo-gastric
nerves, joined by others from the sympathetic system. The fine nervous cords
enter at the root of the lung, and follow the air-tubes. According to Remak, whose
account has been confirmed and added to by the more recent observations of
Stirling and others, they include both white fibres, derived in all probability from
the vagus, and grey filaments proceeding from the sympathetic, and have gaugiion-
cells, both singly and in groups, upon them in their course. In the lower verte-
brates (frog, newt) the nerves are chiefly distributed to a layer of plain muscular
tissue, which is everywhere found taking part in the composition of the relatively
simple pulmonary wall (Stirling). Berkeley has described the nerve-endings in
mammals as forming a plexus of fine fibrils with interspersed stellate cells such as
have been noticed in many glands and mucous membranes. The ultimate ending
appears to be in open arborisations upon and between the alveoli.


v. Bereg-szaszy, Beitrag zur Anatomic und Physiologic des Kehlkopfs, Archiv f. d. gesammte
Physiol., Bd. Ixvi., 1889.

Berkeley, H. J. , The intrinsic pulmonary nerves in mammalia, Johns Hopkins Hosp. Rep.,
vol. v., 1894.

Bowles, R. Li., Observations upon the mammalian pharynx with especial reference to the
epiglottis, Sow:. Anat. and Phys., vol. xxiii., 1889.

Bradford, J. Rose, The innervation of the pulmonary vessels, Proceed, of the Roy. Soc.,
vol. xlv., 1889.

Bradford, J. Rose, and Dean, H. P., The pulmonary circulation, Journ. of Physiol. xvi. ,

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