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per diem, varies within wide limits, with the character of the food
and the duration of its passage through the intestine. Even in the
rectum the process of absorption goes on, and faeces retained here become
dry and hard. The fffices passed on a vegetable diet, or on a diet con-
taining a liberal allowance of vegetables, are both much softer {i.e.
contain more water) and much greater in total quantity of dry solids
than those on a meat diet alone. The increase in the quantity of soHds
is due to the vegetable food containing a much higher percentage of
undigestible tissue. The softer consistency arises from the stimulation of
the mucous membrane by the undigested remnants of the vegetable
tissue, causing increased peristalsis, so hastening the transit through the
intestine, and shortening the period of absorption. This stimulating
action of vegetable food adds greatly to its value in a mixed diet. In
consequence of the absence of this stimulus, the period of deftecation
is greatly prolonged on a purely flesh diet, and may only take place
at intervals of several days. The amount of fasces daily excreted by
man on a mixed diet averages, accordmg to Voit,^ 120 to 150 grms.,
containing 30-37 grms. of dried solids; on a vegetarian diet, the
average amount obtained was 333 grms., containing 75 grms. of dry
material.

Colour. — The colour of the faeces varies greatly, being mainly influ-
enced by the nature of the food. On a diet of meat, the colour is dark
brown to pitch black, due to hasmatin and to ferrous sulphide, formed
by the action on haemoglobin-derivatives, of sulphuretted hydrogen
generated by bacteria in the intestine. Administration of iron or
bismuth salts produces a similar effect. A liberal allowance of bread,
especially of the coarser varieties, in the food, gives rise to light yellow-
coloured faeces. Fat, when eaten in greater quantity than the animal
requires, is excreted with the faeces chiefly as fatty acids and soaps, and

^ Hasebrock, Ztsclir. f. jihysiol. Chem., Strassburg, 1888, Bel. xii. S. 148.
" Ztichr.f. Biol., Miinchen, 1889, Bd. xxv, S. 264,



COMPOSITION OF F.^ECES. 473

causes the fteces to have a yellowish or clay-coloured appearance.
Such fatty stools also result when imperfect fat absorption is caused by
stoppage of the bile duct. The derivatives of bile pigments also con-
tribute to the colour of the feeces/ and part of the brown colour of
normal faeces arises from these, although it is probably due in greater
measure to hsematin. Administration of calomel, by arresting bacterial
decomposition, prevents the reduction of the bile pigment, which then
appears in the faeces as biliverdin, and produces a green colour. The
similar colour of meconium shows that bacteria are absent in the foetal
intestine. Green-coloured fteces are also excreted for some time after
birth, until the normal bacteria of the intestine gradually acquire
possession, when the Ijiliverdin is reduced and the faeces assume a brown
colour.

Reaction. — The reaction of the faeces is also variable. According to
Hammarsten,- they may often be alkaline on the surface, from contact
with the intestinal mucous membrane, while acid within the mass.
Gamgee •' states that the faeces in man are normally alkaline, and very
exceptionally present an acid reaction. Wegscheider '^ found the faeces
normally acid in infants.

Composition. — The faeces are an exceedingly complex mixture, con-
taining substances of various origin and constitution, soluble and
insoluble, derived from the food, the bile, and the detritus of the in-
testinal surface.^ The number of these components is so large, and the
amounts in which they are present so variable, that tables of quantitative
composition possess little value.

The undissolved substances consist of fragments of undigested food,
such as pieces of vegetables, muscle fibres, connective tissue, elastic
fibres, and small masses of casein and fat. The amount of these is
largely increased when the supply of food taken in is more than
sufficient to satisfy the demands of the body. A microscopic examina-
tion further shows epithelial cells derived from the intestine, starch
granules, fat globules, and occasionally crystals of magnesium and
calcium phosphates, and of ammonia-magnesium phosphate. Besides
these, there is present the indigestible residue of various foodstuffs,
such as nucleins from nucleo-proteids, keratin from epidermal struc-
tures, and haematin from haemoglobin.

The mineral salts present vary with the food, but consist chiefly of
the phosphates of the alkaline earths, with small quantities of silica and
phosphate of iron.

The other constituents include mucin, derived from the various
secretions, mainly from the mucous membrane of the intestine ; indol,
skatol, volatile fatty acids, ammonia, sulphuretted hydrogen, and methane,

■^ There is some difference of opinion on this point. Gamgee ( ' ' Physiological Chemistry of
the Animal Body," vol. ii. p. 458) states that the brown colour of normal fpeces is due to
hydrobilirubin ; Hammarsten ("Lehrbneh der physiol. Chemie," Aufl. .3, S. 28-3), that the
decomposition products of the bile pigments have little influence on the normal colour of
the faeces.

2 "Lehrbuch der physiol. Chemie," Aufl. 3, S. 284.

'^ "Physiological Chemistry of the Animal Body," vol. ii. p. 457.

'^ Jahresb. il. d. Fortschr. d. Thicr-Chem., Wiesbaden, 1876, Bd. vi. S. 482.

^ The miicous membrane of the intestine and its secretion furnish a considerable quota
to the fffices ; this is shown by an experiment due to Hermann {Arcli. f. d. ges. Physiol.,
Bonn, 1890, Bd. xlvi. S. 93), who separated a loop of intestine, cleared it of contents, sewed
its two ends together so tliat it formed a ring, restored the continuity of the remainder of
the intestine, and closed the wound. In a few days it Avas found, on killing the animal,
that this loop was filled with a mass resembling ffeces in appearance.



474 CHEMISTR V OF THE DIGESTIVE PROCESSES.

which are formed in bacterial decomposition ; ^ and the products yielded
by the bile, stercobilin, cholesterin, and traces of bile acids.^

Stercolilin^ is a reduction compound of the bile pigments formed
in their passage along the intestine, and is probably identical with
urobilin and hydrobilirubin. Normally, all the bile pigment is reduced
to this substance, but bilirubin has been observed in the fasces under
pathological conditions.

Excretine is a crystalline body, described by Marcet * as occurring
only in human fseces. It is very soluble in boiling alcohol, and may be
mechanically thrown down from an alcoholic extract of the faeces by
adding milk of lime. The precipitate is washed with water, dried and
extracted with a mixture of alcohol and ether. On concentration of the
solution by evaporation, impure excretine crystallises out. This is
dissolved in hot alcohol, decolorised by animal charcoal, and obtained
pure on recrystallisation in acicular four-sided prisms, melting at 92°-
96° C. It is insoluble in water, hot or cold ; sparingly soluble in cold,
readily in hot alcohol ; very soluble in ether ; and the solutions are
neutral in reaction. Its quantitative composition gives the formula
C^gHjsoSOo. Hinterberger ^ states that, by repeated crystallisation, it may
be obtained free from sulphur, and then has the empirical formula
CooHoqO ; with bromine this yields a substitution compound, Go^^^v.f).

Uxcretoleic acid is a body described by Marcet,^ who obtained it on
cooling a hot alcoholic solution of human fteces. On exhausting with
ether, a green ethereal solution is obtained, which, on evaporation, leaves
an oily residue of a dark green colour and acid reaction, melting at
25°-26° C.

Meconium is the name given to the contents of the large intestine in
the foetus, which are expelled at, or after, birth. It is a dark brownish-
green mass of acid reaction. It contains 20 to 30 per cent, of dried
solids, which consist of mucin, bile pigments (biliverdin and bilirubin),
bile acids, cholesterin, fats, fatty acids, calcium and magnesium phos-
phates and sulphates.

In addition it contains a substance giving two absorption bands, one
to the red side of the D line, and the other, broader and darker, between
the D and E lines.

-^ The odonr of the feces arises from tliese bodies. - See p. 391.

^ Vanlair and Masius, Ccntralhl. f. d. med. JVissensch. , Berlin, 1871, No. 24, S. 369;
see also under "Bile," p. 388.

* Med. Times and Gaz., London, 18.58, IST. S., vol. xvii. p. 156.

^ Jnn. d. Chem., Leipzig, 1873, Bd. clxvi. S. 213. ^ Loc. cit.



THE SALIVARY GLANDS.^

By J. IST. Langley.

Contexts : — Anatomical Characters, p. 475 — Histological Characters, -p. All — Origin
and Course of jSTerves, p. 479 — Changes during Secretion, p. 485 — Reflex Secre-
tion, p. 489 — The Dyspnceic Secretion, p. 493 — Stimulation of the Cranial
Nerve, p. 493 — Stimulation of the Sympathetic Nerve ; the Augmented Secre-
tion, p. 494 — Effect of Protracted Stimulation on the Amount and Percentage
Composition of Saliva, p. 498 — Relation of the Rate of Secretion to the Per-
centage Composition of Saliva, p. 499 — Some General Characters of Saliva, p. 501
— Substances secreted in Saliva, p. 503 — Effects of the Cranial and Symjjathetic
Nerves upon the Blood Flow, p. 504 — Mutual Effects of the Cranial and Sym-
pathetic Nerves upon Secretion, j). 506 — Effect of Variations in the Amount
and Quality of the Blood supplied to a Gland, p. 508 — Relation of Secretion to
the Flow of Lymph, p. 510 — The Secretory Pressure, p. 511 — Reflex Inhibition
of Saliva, p. 512 — The Action of Alkaloids, p. 512 — Formation of Heat, p. 516
— Electrical Changes, p. 517 — Section of Glandular Nerves ; the Paralytic
Secretion, p. 519 — Secretion due to Reflex Action of Peripheral Ganglia, p. 523
— Direct Irritability of Gland-Cells, p. 524 — Extirpation of the Glands ; injec-
tion into the Blood of Saliva and of Gland Extracts, ]). 524 — General Con-
siderations ; theories of the Mode of Action of Secretory Nerves, p. 525.

Some Anatomical Chaeacteks of the Salivary Glands.

In the dog and cat, the sublingual gland enlarges at its end, and
loses its flattened form ; the enlarged end is closely attached to the sub-
maxillary gland, and is enclosed in the firm capsule of this gland, so that
at first sight it appears to form part of it.

The ducts from the lobules of the submaxillary gland unite, either
in the connective tissue which stretches from the hilus of the gland, or
in the hilus itself. The gland duct — the duct of "Wharton — runs from
the hilus to its opening underneath the tongue, without receiving, except
in rare cases, any further accession.

The sublingual gland in about its anterior two-thirds consists of
flattened lobules, the ducts of which enter the main duct on its com-se

^ Physiological investigations on the salivary glands have, for the most part, been
carried out on the larger glands, namely, the submaxillary, the parotid, and the sublingual.
But such conclusions as we may be able to form with regard to these, we may apply with
little change to the numerous smaller glands which pour their secretion into the mouth
and pharynx, and, indeed, to the lachrymal glands and glands of the nasal mucous mem-
brane also. Both in histological and physiological characters the lachrymal gland
resembles an albuminous salivary gland. It receives cranial secretory fibres by way of the
lachrymal branch of the fifth nerve ; the origin of these fibres from the medulla has not
been investigated. It receives sympathetic fibres by way of the cervical sympathetic and
the blood vessels of the gland. Secretion can be produced reflexly by stimulating most,
if not all, sensory nerves.

The animals on which investigations have been made are chiefly the dog, cat, and rabbit,
the horse, ox, and sheeji.



476 THE SALIVARY GLANDS.

past them. Thus the gland has no proper hihis. The duct runs parallel
to and a little laterally of Wharton's duct.

The main blood supply, both to the submaxillary and the sublingual
gland, is derived from a branch given off by the external maxillary
artery. The submaxillary division of this branch runs to the hilus of
the gland, and there divides. The submaxillary gland receives also one
or two small branches from the great (or posterior) auricular artery,
where this curls round the digastric muscle.

The veins of the submaxillary gland are variable in position, and
somewhat variable in number. There are generally two ; they run a
short course, about half a centimetre, and then one enters the internal,
and the other the external, maxillary vein, a little before these unite to
form the external jugular vein.

In the dog and cat there is a fairly large gland situated in the orbit,
and hence called the orbital gland. Its duct opens near the second
upper molar tooth. The orbital gland corresponds to the large buccal
gland, which in some animals is called the superior molar.

In the rabbit, the only point we need mention is that the parotid
gland consists of two larger and thicker portions, a medial and a lateral,
connected by a thin central portion. By appropriate arrangement, the
thin central portion can be observed under a microscope, and the appear-
ance of the gland cells in life, and the variations of the blood flow in
varying conditions, can be observed.

Occasionally in the dog, and more constantly in some other animals,
for instance the guinea-pig, a small gland, called by Klein ^ the inferior
admaxillary, pours its secretion into the duct of the parotid. It
may be regarded as a separated lobule of the parotid gland, although
its secretory cells are mucous, instead of being albuminous, thus
differing from the parotid secretory cells in general (cf. below, p. 478).

In a considerable number of animals, a small mucous gland is
attached to the outer anterior end of the submaxillary gland. This
was described by Klein in the guinea-pig, and called by him the superior
admaxillary. The duct of this gland, according to Eanvier, runs parallel
to and on the outer side of Wharton's duct, but does not join it. He
calls it the retrohngual sland.

Eanvier - considers that the customary use of the term sublingual gland is
in many cases erroneous. The sublingual, he defines as a gland which has a
number of separate ducts — the ducts of Rivini. But, besides the sublingual,
another gland occurs, which he calls the retrolingual gland. This is charac-
terised by having a single duct — the duct of Bartholin — running parallel to
Wharton's duct. An animal may have both sublingual and retrolingual, as
the guinea-pig, rat, and hedgehog; or the retrolingual may be absent, as in
man, horse, sheep, and rabbit ; or, again, the sublingual may be absent, as in
the dog and cat. Thus Ranvier considers the gland usually called the sub-
lingual in the dog and cat to be the retrolingual.

In different classes of mammals, the relative development of the
salivary glands varies. Thus in the horse the parotid is four to five times
the weight of the submaxillary gland, in the sheep and ox the weights
are not very different, in the dog the submaxillary gland is slightly
heavier than the parotid.

^ Quart. Journ. Micr. Sc, London, 1881, p. 114.

- " Etude anatomique des glands," Arch, dc jihysiol. norm, et 2')ath., Paris, 1886.



BIS TO L O GICAL CHAR A CTERS.
The following table is taken from Colin : ^ —



477



Weight in Grammes of — >


Parotid.


Submaxillarj'.


Sublingual.


Horse ....

Ox

Sheep ....


400

283

43


86

298

36


23
43

4



Some Histological Characters of the Salivary Glands.

It would be outside the scope of this account to give a detailed
description of the ducts, ductules, terminal tubes, lymphatics, and other
histological features of the several glands. But some of the histological
features have so intimate a relation to physiological observations, that it
is not advisable to pass them by without notice.

The narrow ductule, proceeding from a duct, commonly divides, and
each secondary ductule widens more or less suddenly into a tube of
secreting cells ; each tube gives off curved branches, and these also may
give off similar branches ; thus, a clump of tubes is formed around the
primary ductule. The terminal tubes are usually called alveoli, and their
cells alveolar cells.

The alveolar cells may be classified according to the chemical nature
of the substances they secrete. A step in this direction was taken by
Heidenhain, who divided the cells into mucous cells which secrete mucin,
and albuminous cells which secrete some form of proteid. There is good
evidence that the typical albuminous cell does not secrete any mucin,
and there is some evidence that the typical mucous cell does not secrete
any proteid, and on this basis it is apt to be assumed that all the alveolar
cells secrete either mucin only, or proteid only. It should, however, be
remembered that this is an assumption ; it is possible that some alveolar
cells secrete both mucin and proteid.

In any one salivary gland all the alveolar cells may be mucous or
all may be albuminous, or some of them may be mucous and some
albuminous. Further, in different glands, the relative number of the
two kinds of cells varies in nearly all possible proportions. The
nomenclature in use takes notice of the broad distinctions only. Glands
which consist almost entirely of albuminous cells are called albuminous
glands, those which consist chiefly of mucous cells are called mucous
glands. The glands of intermediate structure are commonly placed
in the class of mucous glands, unless the proportion of mucous to
albuminous cells is very small.

The term "mixedgland" was introduced for certain special cases; for example,
the submaxillary gland of the guinea-pig, in which one or more lobules were
said to be mucous and the rest to be albuminous. But in the guinea-pig, and
possibly in the other cases, the mucous lobule appears to be a separate gland
(cf. above, p. 476). It would probably he more convenient to use the term
" mixed," for a gland in which the mucous and albuminous cells are present
in approximately equal proportions. And we might have the following scale,
passing from entirely albuminous to entirely mucous : — albuminous glands,
1 "Traits de physiol. comparee des animanx," 3rd edition, 1886, tome i.



478 THE SALIVAR Y GLANDS.

muco-albuminous glands, mixed glands, albumino-miicous glands, demilune
glands, mucous glands.

The demilune cells, there can be little doubt, are albuminous
secretory cells.^ If we compare a series of submaxillary glands, passing
from albuminous to mucous, we find that the albuminous cells become
more and more confined to the ends of the terminal tubes, and the fewer
there are the more compressed they become by the mucous cells, a
feature, however, which is more marked in hardened than in fresh
glands. And when the gland secretes, the demilune cells show obvious
signs of secretory activity. The small discrete granules in them
diminish in number, and in some animals form an inner granular zone ;
in alcohol-hardened glands, the demilune cells stain more deeply with
carmine, and the nuclei and nucleoli are more conspicuous. The cells
diminish in size after prolonged activity of the gland. In the earlier
stages of secretion they appear to be larger, but this is probably due to
a diminution in the size of the mucous cells, and so of the whole tube,
whereby the demilune cells are less flattened.

A comparison of the large salivary glands in different mannnals
shows that the parotid has least variation in structure, and the sub-
maxillary gland the most.

The parotid gland, as a rule, contains albuminous cells only ; but
in the dog there are commonly, if not always, a few mucous cells,
or mucous alveoli present. And there may be in the dog a small
mucous lobule, pouring its secretion into tlie duct a short distance from
the main gland.

The submaxillary glands are entirely albuminous in rodents. In
primates, the majority of the cells are albuminous, but some are mucous.
In solipedes and ruminants, the glands are " mixed," but most of the
cells are mucous. In carnivora the great majority of the alveolar cells
are mucous, but some are albuminous, and there are fewer albuminous
cells in the submaxillary gland of the dog than in that of the cat ;
thus in a microscopical preparation of the gland of a dog, the albuminous
cells are almost entirely in the form of demilunes, whilst in a similar
preparation of the gland of a cat, a considerable number of albuminous
alveoli are seen. In the mole, large portions of the submaxillary gland
do not even contain demilunes, and in these portions none but typical
mucous cells occur.

The sublingual gland in all animals contains a greater or less
proportion of mucous cells, and it is in consequence generally called
a mucous gland. But as it always contains albuminous cells also
it belongs properly to the class of mixed glands. The sublingual gland
has certain characters which distinguish it from the submaxillary gland.
It is more obviously tubular, the lumina are often large, the cells in a
section of a hardened specimen are more columnar, and a considerable
number of them consist, in their ordinary resting state, of proteid
material in the outer third, half, or even two-thirds, and of mucous
material in the remaining portion next the lumen.

The orbital gland - of the dog is mucous, the mucous cells are large and
contain very little proteid substance, the demilunes are much flattened. The

1 Laiigley, Trans. Internat. Med. Cong., 1880 ; Proc. Roy. Soc. London, vol. xi. p.
364 ; and this view has been taken by most subsequent observers.

' Of. Lavdowsky, Arch. f. 'iidkr. Anal., Bonn, 1877, Bd. xiii. p. 288.



ORIGIN AND COURSE OF NERVES. 479

aduiaxillary glands (Klein) have been found, so far as they have been
investigated, to be mucous glands.

One or two points w^ith regard to the structure of the alveolar cells,
which bear upon questions we have to consider later, we may also
mention.

In all salivary alveolar cells there are found, though with very
different degrees of distinctness, more or less spherical granules, destined
in an altered or unaltered condition to become part of the secretion.
Whether the cell substance, in which the granules are embedded, lias
or has not a definite structure, we cannot decide with certainty; this
cell substance may be what we speak of as granular structureless
protoplasm ; or it may consist of two parts, — a protoplasmic part form-
ing externally a boundary layer, except perhaps towards the lumen,
and internally a delicate network ; and another part between the net-
work and the granules, which in some cells may be of an albuminous
and in others of a mucous nature.

Every gland has its own distinctive histological features, implying a
distinctive chemical character in the substance it secretes. In addition,
secreting cells of obviously different nature often occur in the same gland.
Thus, in the submaxillary gland of the rat, there is an ordinary albuminous
portion, and running through this are tubes, in bold curves, consisting of cells
with large granules, which sometimes leave an outer clear zone. And in the
submaxillary gland of the rabbit, the first cells of the alveoli, and the terminal
ductules, have in the fresh state conspicuous granules, differing widely from
the faint granules of the rest of the cells in the alveoli.

Okigin and Course of the JSTeeves to the Salivary Glands.

All the salivary glands are supplied with nerve-fibres from two
sources. They receive nerve-fibres, on the one hand, from the medulla
oblongata, by way of some cranial nerve ; and, on the other hand, from
the spinal cord, by way of the cervical sympathetic.

The cranial nerve contains many, the sympathetic nerve comparat-
ively few, secretory fibres. The cranial nerve contains vaso-dilator,
and the sympathetic nerve contains vaso-constrictor fibres for the small
arteries of the glands. There is, at present, no evidence worth con-
sidering that the cranial nerves have vaso-constrictor fibres for the
glands, or that the sympathetic nerve has vaso-dilator fibres for them.

The chorda tympani and the nerve-cells with which it is
connected. — The submaxillary, the sublingual glands, and the glands
of the tongue, receive secretory and vaso-dilator fibres from the chorda
tympani. The chorda tympani arises from the seventh nerve ; it leaves
this in the Fallopian canal, runs across the tympanum, and joins the



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 68 of 147)