mode of termination is unknown, but they probably go to the blood-
vessels and to the muscular tissue in the capsule and trabeculse. [They
are well seen in the spleen of the ox, and in their course very small
ganglia placed wide apart, have been found by Kemak and W. Stirling.]



Chemical Composition. Several of the more highly oxidised stages of albu-
minous bodies exist in the spleen. Besides the ordinary constituents of the blood,
there exist : leucin, tyrosin, xanthin, hypoxanthin ; also lactic, butyric acetic,
formic, succinic, and uric acids, and perhaps glycero-phosphoric acid (Salkowski) ;
Cholesterin, a glutin-like body, inosite, a pigment containing iron, and even free
iron oxide (Nasse). The ash is rich in phosphoric acid and iron poor in chlorine
compounds. The splenic juice is alkaline in reaction ; the specific gravity of the



FUNCTIONS OF THE SPLEEN. 207

spleen = 1059 - 1066. [The watery extract of the spleen contains a proteid combined
with iron.]

The Functions of the spleen are. obscure, but we know some facts on
which to form a theory. [The spleen differs from other organs in that
no very apparent effect is produced by it, so that we must determine
its uses in the economy from a consideration of such facts as the follow-
ing (1.) The effects of its removal or extirpation. (2.) The changes
which the blood undergoes as it passes through it. (3.) Its chemical
composition. (4.) The results of experiments upon it. (5.) The
effects of diseases.]

(1.) Extirpation. The spleen may be removed from an animal
without the organism suffering any very obvious change (Galen). The
human spleen has been successfully removed by Koberle, Pe"an,
Zacaralla (1849), and others. As a result (compensatory ?) the lym-
phatic glands enlarge, but not constantly, while the blood-forming
activity of the red marrow of bone is increased. Small brownish-red
patches were observed in the intestines of frogs after extirpation of the
spleen. These new formations are regarded by some observers as com-
pensatory organs. Tizzoni asserts that new splenic structures are
formed in the omentum (horse, dog) after the destruction of the
parenchyma and blood-vessels of the spleen. The spleen is absent
extremely seldom (Meinhard, Koch, and Wachsmuth). [Schindeler
found that animals after extirpation of the spleen became very
ravenous, but there was no other marked symptom.]

Schiff stated that after extirpation of the spleen, the pancreatic juice failed to
digest proteids. The evidence in support of this statement is unsatisfactory, and
Mosler affirms that this operation has no effect either on gastric or pancreatic diges-
tion. Heidenhain also found a similar negative result. The operation ought to
be performed on young animals, as old animals often succumb to it.

(2.) According to Gerlach and Funke the spleen is a BLOOD-FORMING
GLAND. As already mentioned (p. 20) the blood of the splenic vein
contains far more colourless corpuscles than the blood of the splenic
artery. Many of these corpuscles undergo fatty degeneration, and
disappear in the blood-stream (Virchow). That colourless blood-cor-
puscles are formed within the spleen seems to be proved by the
enormous number of these corpuscles which are found in the blood
in cases of hyperplasia of the spleen or leukaemia (Bennett, 1852,
Virchow). Bizzozero and Salvioli found that several days after severe
hsemorrhage, the spleen became enlarged, and its parenchyma contained
numerous red nucleated hsemato -blasts.

According to Schiff, extirpation of the spleen has no effect, either upon the
absolute or relative number of coloured or colourless corpuscles. [According to
the more accurate observations of Picard and Malassez, there is a temporary



208 FUNCTIONS OF THE SPLEEN.

diminution of the coloured blood-corpuscles and their haemoglobin, after extirpa-
tion of the spleen.]

(3.) Other observers (Kolliker and Ecker) regard the spleen as an
organ in which COLOURED BLOOD-CORPUSCLES ARE DESTROYED, and they
consider the large protoplasmic cells containing pigment granules (p. 1 6)
as a proof of this. According to the observations of von Kusnetzow,
these structures are merely lymph-corpuscles, which, in virtue of their
amoeboid movements, have entangled coloured blood-corpuscles. [Such
corpuscles exhibit similar properties when placed upon a warm stage.]
Similar cells occur in extravasations of blood (Virchow). The coloured
blood-corpuscles within the lymph-cells gradually become disintegrated,
and give rise to the production of granules of hsernatin and other
derivatives of haemoglobin. Hence, the spleen contains more iron than
corresponds to the amount of blood present in it. When we con-
sider that the spleen contains a large number of extractives derived
from the decomposition of proteids, it is very probable that coloured
blood-corpuscles are destroyed in the spleen. Further, the juice of the
spleen contains salts similar to those that occur in the red blood-
corpuscles.

The blood of the spleen is said to undergo other changes, but the following
statements must be accepted with caution : The blood of the splenic vein contains
more water and fibrin ; its red blood-corpuscles are smaller, brighter, less flattened,
more resistant, and do not form rouleaux ; its haemoglobin crystallises more easily,
and there is a larger proportion of O during digestion.

[It would thus appear that the spleen has a very direct relation
to the blood; that coloured blood-corpuscles undergo disintegration,
and that colourless corpuscles are manufactured within it.]

(4.) Contraction. In virtue of the plain muscular fibres in its
capsule and trabeculse, the spleen undergoes variations in its volume
(Kolliker). Stimulation of the spleen (Rud. Wagner, 1849) or its
nerves, by cold, electricity, quinine, eucalyptus, ergot of rye, and other
" splenic reagents " (Hosier) causes it to contract, whereby it becomes
paler, and its surface may even appear granular. After a meal,
the spleen increases in size, and it is usually largest about five
hours after digestion has begun i.e., at a time when the digestive
organs have almost finished their work, and have again become less
vascular. After a time it regains its original volume. For this reason
the spleen was formerly regarded as an apparatus for regulating the
amount of blood in the digestive organs.

[The congestion of the spleen after a meal is more probably related
to the formation of new colourless corpuscles than to the destruction of
red corpuscles. It may be, however, that some of the products of



CONTRACTION OF THE SPLEEN.



209



digestion are partially acted upon in the spleen, and undergo further
change in the liver.]

There is a relation between the size of the spleen and that of the
liver, for it is found that when the spleen contracts e.g., by stimulation
of its nerves the liver becomes enlarged as if it were injected with
more blood than usual (Drosdow and Botschetschkarow).

[Oncograph. Botkin, and more recently Roy, have studied various
conditions which affect the size of the spleen. Roy's observations
are most important. He enclosed the spleen of a living animal (dog)
in a box with rigid walls, and filled with oil after the manner of the
plethysmograph ( 101). Any variations in the size of the organ
caused a variation in the amount of oil within the box, and these
variations were recorded. This instrument Roy termed an " ONCO-
GRAPH" (oyxoc, volume). The blood-pressure was recorded at the
same time.

Roy finds that the circulation through the spleen is peculiar, and
that it is not due to the blood-pressure within the arteries, but is
carried on chiefly by a rhythmical contraction of the musculaf fibres of
the capsule and trabeculse. The spleen undergoes very regular rhyth-
mical contractions (systole) and dilatations (diastole). This alternation



Fig. 91.

Tracing of a splenic curve, reduced one-half, taken with the oncograph. The upper
line with large waves is the splenic curve, each ascent corresponds to an
increase, and each descent to a diminution in the volume of the spleen. The
curve beneath is a blood-pressure tracing from the carotid artery. The lowest
line indicates the time, the interruptions of the marker occurring every two
seconds. The vertical lines, a and 6, give the relative positions of the lever
point of the oncograph, and of the point of the recording style of the kymograph
respectively (Roy).



210 INFLUENCE OF NERVES ON THE SPLEEN.

of systole and diastole may last for hours, and the two events together
occupy about one minute (Fig. 91). Changes in the arterial blood-
pressure have comparatively little influence on the volume of the spleen.
The rhythmical contractions, although modified, still go on after section
of the splenic nerves. This would seem to indicate that the spleen has
an independent (nervous) mechanism within itself causing its move-
ments.]

Influence of Nerves. Section of the splenic nerves causes an
increase in the size of the spleen ; and when the nerves at the hilum
are extirpated it swells and assumes a deep purple colour. The nerves
have their centre in the medulla oblongata, and so far they are com-
parable to vaso-motor nerves. Stimulation of the medulla oblongata,
either directly or by means of asphyxiated blood, causes contraction of
the spleen [hence, the spleen is "small and contracted" in death
from asphyxia.] The fibres proceed down the cord, and . are probably
joined by other fibres derived from ganglion cells lying opposite the
first to the fourth cervical vertebrae, which cells also act on the spleen.
The fibres leave the cord in the dorsal region, enter the left splanchnic,
pass through the semi-lunar ganglion, and thus reach the splenic plexus
(Jaschkowitz.) Stimulation of the peripheral ends of these nerves
causes contraction of the spleen, and so does cold applied to the spleen
directly or over the region of the organ. In this last case the result
is brought about reflexly. Section or paralysis of these nerves causes
dilatation, and so does curara or continued narcosis (Bulgak). [Botkin
found that the application of the induced current to the skin over the
spleen, in a case of leukaemia, caused well-marked contraction of the
spleen in all its dimensions ; the spleen becoming firmer, and its surface
more irregular. The result lasted much longer than the duration of
the stimulus. The same occurred in a case of enlarged lymphatic
glands. After a time the organ began to enlarge. After every stimu-
lation the number of colourless corpuscles in the blood increased, and
the condition of the patient improved.]

[There is a popular notion that the spleen is influenced by the condition
of the nervous system. Botkin found that depressing emotions in-
creased its size, while exhilarating ideas diminished it. The causes of
these changes are referable not only to changes in the amount of blood
in the spleen, but also to the greater or less degree of contraction of.
its muscular tissue. And it would appear that, like the small arteries,
the muscular tissue of the spleen is in a state of tonic contraction. The
size of the spleen may be influenced reflexly. Thus, Tarchanoff found
that stimulation of the central end of the vagus, when the splanchnics
were intact, caused contraction of the spleen, while stimulation of the
central end of the sciatic also caused contraction, but to a less degree.



INFLUENCE OF NERVES ON THE SPLEEN. 211

It is quite certain that all the phenomena are not due to the action of
vaso-motor nerves on the splenic blood-vessels. There is a certain
amount of independent action of the muscular fibres of the organ, and
it is not improbable that the innervation of the spleen is similar to the
innervation of arteries, and that it has a motor centre in the cord
capable of being influenced by afferent nerves, and sending out efferent
impulses.]

[Roy confirmed most of these results, and found that stimulation of
(1) the central end of a sensory nerve, (2) of the peripheral ends of
both splanchnics, (3) of the peripheral ends of both vagi, caused
contraction of the spleen. But even after section of the splanchnics
and vagi, stimulation of a sensory nerve still caused contraction, so
that there must be some other channel as yet unknown. Boche-
fontaine found that electrical stimulation of certain parts of the cortex
cerebri produced contraction of the spleen.] Sensory nerves seem to
occur only in the peritoneum covering the spleen.

Pressure on the splenic vein causes enlargement of the spleen (Moslec) ; hence,
increased pressure in this vein (congestion of the portal vein, cessation of haemor-
rhoidal and menstrual discharges) also causes its enlargement. With regard to the
action of "splenic reagents," such as Quinine, on the contraction of the spleen,
Binz is of opinion that this drug retards the formation of the colourless blood-cor-
puscles, so that its chief function is interfered with and the organ becomes less
vascular. It is not definitely decided, however, whether it is contraction or dilata-
tion of the spleen that alters the proportion of red and white corpuscles in the blood.

Splenic Tumours. The increase in size of the spleen in various diseases early
attracted the attention of physicians. The healthy spleen undergoes several varia-
tions in volume during the course of a day, corresponding with the varying activity
of the digestive organs. In this respect the spleen resembles the arteries. In
many fevers the spleen becomes greatly enlarged, probably due to paralysis of its
nerves. It is greatly increased in intermittent fever or ague, and often during
the course of typhus. When it becomes abnormally enlarged, and remains so after
repeated attacks of ague, it is greatly hypertrophied and constitutes "ague cake."
In cases of splenic leuksemia it is greatly enlarged, and at the same time there is a
great increase in the number of colourless corpuscles in the blood, and also a
decrease of the coloured ones (p. 23).



II. The Thymus.

During foetal life this gland is largely developed, and it increases during the first
two or three years of life, remaining stationary until the tenth or fourteenth year,
when it begins to atrophy and undergo fatty degeneration. [The degeneration
begins at the outer part of each lobule and progress inwards (His).]

Structure. [" It consists of an aggregation of lymph-follicles (resembling the
glands of Peyer) or masses of adenoid tissue held together by a framework of con-
nective tissue which contains blood-vessels, lymphatics, and a few nerves (Fig. 92).
The framework of connective tissue gives off septa which divide the gland into lobes,
these being further subdivided by finer septa into lobules, the lobules being separated



212 THE THYMUS.

by fine intra-lobular lamellae of connective tissue into follicles (0*5 -1 '5 mm.).
These follicles make up the gland substance, and they are usually polygonal when
seen in a section. Each follicle consists of a cortical and a medullary part, and the
matrix or framework of both consists of a fine adenoid reticulum whose meshes
are filled with lymph-corpuscles " (Fig. 93, a).] Many of these corpuscles
exhibit various stages of disintegration. In the medulla are found the concentric
corpuscles of Hassall. ["They consist of a central granular part, around which are
disposed layers of flattened nucleated endothelial cells arranged concentrically.
When seen in a section they resemble the 'cell-nests ' of epithelioma (Fig. 93, b).





Fig. 92. Fig. 93.

Section of the thymus gland of a cat, showing Elements of the thymus ( x 300)
one complete lobule with an outer cortical a, lymph-corpuscles ; 6, con-
part, a centre, b, and parts of adjoining centric corpuscle of Hassall.
lobules a, lymphoid tissue; c, blood-
vessels injected ; d, connective tissue.



They have also been compared to similar bodies which occur in the prostate.
They are most numerous when the gland undergoes its retrograde metamorphosis."]

Simon, His, and others described a convoluted blind canal, the " central canal,"
as occurring within the gland, and on it the follicles were said to be placed. Other
observers, Jendrassik and Klein, either deny its existence or regard it merely as a
lymphatic or an artificial product. Numerous fine lymphatics penetrate into the
interior of the organ, and many are distributed over its surface, but their mode of
origin is unknown. [They seem to be channels through which the lymph-cor-
puscles are conveyed away from the gland.] Numerous blood-vessels are also dis-
tributed to the septa and follicles (Fig 92, c).

Chemical Composition. Besides gelatin, albumin, soda-albumin, there are
sugar and fat, leucin, xanthin, hypoxanthin, formic, acetic, butyric, and succinic
acids. Potash and phosphoric acid are more abundant in the ash than soda,
calcium, magnesium (? ammonium), chlorine, and sulphuric acid (v. Gorup-



[Function. As long as it exists, it seems to perform the functions of a true
lymph-gland. This view is supported by the fact that in reptiles and amphibians,
which do not possess lymph-glands, the thymus remains as a permanently active
organ. That the thymus forms colourless corpuscles was first maintained by
Hewson, and confirmed by His and Jendrassik. Extirpation (Friedleben) gave few



THE THYROID.



213



positive results, but chemical investigation shows that the parenchyma contains a
large number of products indicating considerable metabolic activity. The volume
of the gland undergoes variations both in health and disease,]



III. The Thyroid.



Structure. In a connective tissue net- work rich in cells there lie numerous
completely closed sacs (0'04 O'l mm. in diameter), which in the embryo and the
newly-born animal are composed of a membrana propria lined by a single layer of
nucleated cubical cells (Fig. 94). The sacs contain a transparent, viscid, albuminous
fluid. [Xot unfrequently the
sacs contain many coloured
blood-corpuscles (Baber). As
in other glands, there are
lobes and lobules.] Each sac
is surrounded by a plexus of
capillaries which do not pene-
trate the membrana propria.
There are also numerous
lymphatics. At an early
period the sacs dilate, their
cellular lining atrophies, and
their contents undergo colloid
degeneration. When the
gland vesicles are greatly
enlarged, "goitre" is pro-
duced.

The Chemical Composi-
tion of this gland has not
been much investigated. In
addition to the ordinary con-
stituents, leucin, xanthin,
sarkin, lactic, succinic, and
volatile fatty acids have been
found.

Functions. Its functions are quite unknown. Perhaps it may be an apparatus
for regulating the blood supply to the head (?). It becomes enlarged in Basedow's
disease, in which there is great palpitation, as well as protrusion of the eyeball
[Exophthalmos], which seem to depend upon a simultaneous stimulation of the
accelerating nerve of the heart, and the sympathetic fibres for the smooth muscles
in the orbital cavity and the eyelids, as well as of the inhibitory fibres of the
vessels of the thyroid. In many localities it is common to find swelling of the
thyroid constituting goitre, which is sometimes, but far from invariably, associated
with idiocy and cretinism.




Fig. 94.

Section of the thyroid gland ( x 250) cr, small
closed vesicles lined by low columnar epithe-
lium; b, colloid masses distending the vesicles ;
c, connective tissue between the vesicles.



IV. The Supra-Renal Capsules.

Structure. These organs are invested by a thin capsule which sends processes
into the interior of the organ. They consist of an outer (broad) or cortical layer
and an inner (narrow) or medullary layer. The former is yellowish in colour, firm
and striated, while the latter is softer and deeper in tint. In the outermost zone
of the cortex (Fig. 95, &), the trabeculse form polygonal meshes which contain the



214



THE SUPRA-RENAL CAPSULES.



cells of the gland substance ; in the broader middle zone, the meshes are elongated
and the cells filling them are arranged in columns radiating outwards. Here the
cells are transparent and nucleated, often containing oil globules ; in the innermost

narrow zone the polygonal arrangement
prevails, and the cells often contain
yellowish-brown pigment. In the medulla
(c) the stroma forms a reticulum contain-
ing groups of cells of very irregular shape.
Numerous blood-vessels occur in the
gland, especially in the cortex. [The
nerves are extremely numerous, and are
derived from the renal and solar plexuses.
Many of the fibres are medullated. After
they enter the gland, numerous ganglionic
cells occur in the plexuses which they form.
Indeed, some observers regard the cells of
the medulla as nervous. Undoubtedly,
numerous multipolar nerve-cells exist with-
in the gland.] (Eberth, Creighton, v.
Brunn).

Chemical Composition. The supra-

renals contain the constituents of connec-
tive-tissue and nerve-tissue; also leucin,
hypoxanthin, benzoic, hippuric, andtauro-
cholic acids, taurin, inosit, fats, and a body
which becomes pigmented by oxidation.
Amongst inorganic substances potash and
phosphoric acid are most abundant.

The function f the supra-renal bodies
is quite unknown. It is noticeable, how-
ever, that in Addison's disease ("bronzed
skin ") which is perhaps primarily a
nervous affection, these glands have fre-
quently, but not invariably, been found
to be diseased. Owing to the injury to
adjacent abdominal organs extirpation of
these organs is often, although not always,
fatal. Brown-Se"quard thinks they may
be concerned in preventing the over-production of pigment in the blood.




Fig. 95.

Section of a human supra-renal capsule
a, capsule ; b, gland cells of the
cortex arranged in columns; c,
glandular net- work of the medulla ;
d, blood-vessels.



V. Hypophysis Cerebri Coccygeal and Carotid

Glands.



The hypophysis Cerebri, or pituitary body, consists of an anterior lower or
larger lobe partly embracing the posterior lower or smaller lobe. These two lobes
are distinct in their structure and development. The posterior lobe is a part of
the brain, and belongs to the infundibulum. The nervous elements are displaced
by the ingrowth of connective-tissue and blood-vessels. The anterior portion
represents an inflected and much-altered portion of ectoderm, from which it is
developed. It contains gland-like structures, with connective-tissue, lymphatics
and blood-vessels, the whole being surrounded by a capsule. According to Ecker
and Mihalkowicz, it resembles the supra-renal capsule in its structure, while,



COMPARATIVE PHYSIOLOGY OF THE CIRCULATION. 215

according to other observers, in some animals it is more like the thyroid. Its
functions are entirely unknown.

Coccygeal and Carotid Glands. The former, which lies on the tip of the
coccyx, is composed, to a large extent, of plexuses of small more or less cavernous
arteries, supported and enclosed by septa and a capsule of connective-tissue
(Luschka). Between these lie polyhedral granular cells arranged in net- works.
The carotid gland has a similar structure (p. 124). Their functions are quite
unknown. Perhaps both organs may be regarded as the remains of embryonal
blood-vessels (Arnold).

104. Comparative.

The heart in fishes as well as in the larvse of amphibians with gills, is a simple
venous heart consisting of an auricle and a ventricle. The ventricle propels the
blood to the gills where it is oxygenated (arterialised) ; thence it passes into the aorta
to be distributed to all parts of the body, and returns through the capillaries of the
body and the veins to the heart. The amphibians (frogs) have two auricles and
one ventricle. From the latter there proceeds one vessel which gives off the pul-
monary arteries, and as the aorta supplies the rest of the body with blood, the
veins of the systemic circulation carry their blood to the right auricle, those of the
lung into the left auricle. In fishes and amphibians there is a dilatation at the
commencement of the aorta, the bulbus arteriosus, which is partly provided with
strong muscles. The reptiles possess two separate auricles, and two imperfectly
separated ventricles. The aorta and pulmonary artery arise separately from the
two latter chambers. The venous blood of the systemic and pulmonary circulations
flows separately into the right and left auricles, and the two streams are mixed in the
ventricle. In some reptiles the opening in the ventricular septum seems capable of
being closed. The crocodile has two quite separate ventricles. The lower vertebrates
have valves at the orifices of the venae cavse, which are rudimentary in birds and