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the microscope appears as very fine particles, or groups of particles.
On irrigating such a specimen with dilute mineral acid, the particles
are dissolved. The saliva also may contain leucocytes, and will certainly
do so if it has been allowed to stay long in the gland ducts. In ordinary
experimental conditions, leucocytes collect in the connective tissue of
the glands, and migrate, at times in large numbers, into the ducts. The
leucocytes at first show amoeboid movement ; later, they swell, become
vacuolated, and form the bodies which have been called salivary cor-
puscles. The saliva may also contain some cells from the ducts
which have been separated or injured by insertion of the cannula,
some isolated nuclei, either of duct cells or of leucocytes, and occasionally
a few small fat globules.



50 2 THE SALIVARY GLANDS.

In viscid saliva of the submaxillary gland of the dog, spheres or
clumps of secreted substance are present. The number and the
character of these vary broadly with the viscidity of the freshly-secreted
saliva, and are, so far as I have seen, independent of the way in which
the secretion is brought about. As sympathetic saliva is usually much
more viscid than chorda saliva, it usually contains these constituents in
much larger number.^

The spheres vary in appearance. In the more viscid specimens of
saliva they are pale, have a very faint outline, and appear homogeneous
(pale spheres). As a rule they are 2 to 4 /a in diameter, but
larger and smaller ones occur. In the less viscid specimens of saliva
some spheres like these are also found, but most are more watery-
looking and are still paler (very pale spheres) ; they vary much in size,
but on an average are larger ; they are apparently the swollen forms of
the ordinary pale sj^heres. There are also, especially in more watery
saliva, spheres which differ from the preceding in having a fairly sharp
outline (vacuolar spheres). In the more viscid forms of saliva, clumps
occur as well as the pale spheres, and they are more numerous the more
viscid the saliva.

In saliva freshly secreted and freshly examined, the spheres and
clumps may easily escape notice, even though they be present in
hundreds in the field of the microscope. On standing they become
more distinct, and they become obvious at the periphery of the drop,
when they are still barely visible in the centre. In sufficiently viscid
saliva the spheres and clumps are much distorted at the edge of the
drop, and in still more viscid saliva most of them are drawn out into
elongated masses.

Acetic acid, 'S per cent, up to nearly glacial, makes the spheres and
clumps very refractive and rather oily-looking. G-lacial acetic acid
causes them to swell up and become pale, and the clumps usually
become vacuolated. Sodium hydrate causes them to swell up and
disappear.

When saliva containing spheres and clumps is allowed to stand,
these bodies slowly settle, forming, as they do so, masses often of
considerable size. The addition of an equal volume of 5 to 20 per cent,
sodium chloride allows them to sink much more rapidly ; they make
a white, slightly adherent, but not viscid layer at the bottom of the
vessel.

On irrigating viscid saliva under a cover-slip, the fluid added mixes but
slowly with the saliva, so that, instead of irrigating, it is sometimes better to
mix a small drop of saliva with a small drop of the reagent, and to place a
cover-slip on the mixture. Water causes the spheres and clumps to disappear,
hut up to a certain point they can again be made visible by acetic acid; 1 per
cent. NaCl or NagCOg makes the outlines of the bodies more distinct ; 1 per cent,
osmic acid causes them to swell up and take a faint brown tint. Methylene-
blue dissolved in NaoCOg, 1 per cent, stains them, hut as a rule not very quickly.
Picrocarmine, safranin, and other reagents stain them slowly. When saliva
is mixed with one to two volumes of dilute neutral or alkaline salts, dilute or

^ Eckhard, Ztschr. f. rat. Med., 1866, Bd. xxviii. S. 120, found the sympathetic saliva
from the parotid gland of the horse to be wliitish and to contain fine particles. Schiff,
"Leijons sur la digestion," p. 293, found the same with the first drops of saliva secreted
rellexly after a pause. The characters described Avere no doubt due to a precipitation of
calcium salts in the saliva contained within the ducts.



SUBSTANCES SECRETED IN SALIVA. 503

strong acids, the spheres and clumps gradually disappear. In strong solutions
of neutral salts {e.g. 20 per cent, sodium chloride), they may be kept for months
at any rate. Strong alcohol and mercuric chloride cause them to shrink and
make them irregularly granular. Flemming's fluid turns many of them into
vacuolated spheres, with sharp outline and a few distinct small granules. No
mucous cells are seen in saliva after treatment with any of these reagents.

In the submaxillary saliva of the cat, vacuolar and pale spheres are found,
but not the larger clumps.

Microscopical constituents in saliva have been described by Eckhard,
Kiihne, and Heidenhain. The account I have given above differs in several
points from theirs.

The most obvious view to take of these microscopical constituents
of saliva is, I think, that some of the mucous granules are turned bodily
out of the alveolar cells,^ the fluid passing through the cells being
insufficient to dissolve them ; and that by swelling up or massing
together they make the various forms of spheres and clumps which are
seen. But although the mucous granules behave with some reagents
very much as do the small spheres of saliva, and have in some states
very much the same appearance, their behaviour with acetic acid is
strikingly different. The mucous granules, on treatment with dilute
acetic acid, swell up and burst like bubbles ; ^ the spheres in saliva, as we
have seen, become refractive and obvious. Although it is possible that
this difference may depend on differences in the surrounding fluids, it is
sufficient to prevent more than a provisional acceptance of the view
that the spheres of saliva are simply undissolved mucous granules.

Substances which ake or which may be seceeted in Saliva.^

In saliva obtained from mucous glands, the chief organic constituent
is naturally mucin. Little is known with certainty of the varieties of
mucin which exist. In mucous saliva, whilst most of the mucin is
precipitated by acetic acid as a stringy lump, there is not infrequently
a portion which is precipitated in fine particles, these making the fluid
cloudy. A small quantity of proteid is also present, probably belonging
to the class of globulins.

In saliva obtained from albuminous glands the proteid constituents
are globulin (or a body allied to globulin), alkali albuminate, and a
small amount of serum albumin.'^

In typical mucous saliva, diastatic ferment is either absent, or
present in mere traces ; in saliva from albuminous glands, the amount
of diastatic ferment is variable and independent of the percentage of
proteid, but in the saliva of any one gland the diastatic action increases
with the percentage of proteid present.

The salts are, so far as is known, the same in mucous and in
albuminous saliva, although their percentage amount varies considerably
in the saliva obtained from different glands. The bases found are
sodium, potassium, calcium, and magnesium ; the acids are hydrochloric
acid, carbonic acid, phosphoric acid, and sulphuric acid. Sodium
chloride is by far the largest constituent ; after this comes usually

1 Langley, Proc. Roy. Soc. London, 1886, vol. xi. p. 202.

" Langley, Jourii. Physiol., Cambridge and London, 1889, vol. x. p. 433.

* See also article on " Composition of Saliva," p. 342.

^ Kiihne, "Lehrbuch. d. Physiol.," 1866.



504 THE SALIVAR Y GLANDS.

sodium carbonate ; calcium carbonate and calcium phosphate are kept
in solution by the excess of carbonic acid, and precipitated as the gas
escapes.

Saliva yields to a vacuum about twenty vols, per cent, of carbonic
acid, and small quantities of oxygen and nitrogen ; ^ the carbonic acid,
however, is all or nearly all combined with sodium carbonate to form
sodium bicarbonate.

In the saliva of man, potassium sulphocyanate is normally present.^

The alkalinity of saliva depends upon the presence of sodium
carbonate. In man and in the dog the percentage of this salt varies
from O^OS to 0-19 per cent.

In disease,^ traces of other substances have been found in the saliva
of man, for example, urea and leucine. In diabetes, lactic acid has been
found in the saliva; the presence of sugar has been denied by most
observers, but , affirmed by some. In jaundice, saliva does not usually
contain either bile acids or bile pigments, but in some instances traces
are said to occur. In cases of poisoning with salts of mercury, lead, and
some other metals, small quantities of the salts may be present in
saliva ; it is stated, however, that the salts of arsenic are not secreted by
the salivary glands.

An investigation into the character of the substances which can and
which cannot be secreted by the salivary glands, would undoubtedly
lead to interesting and valuable information. It is possible that, with
bodies not acted on chemically, the size of the molecule is the determin-
ing factor. A beginning of such inquiry, though not from this point of
view, was made by Bernard.^ He experimented on the secretion from
the submaxillary and parotid glands of the dog, and on the parotid
glands of the horse. He found that potassium iodide was very readily
secreted, whilst neither sugar,^ ferrocyanide of potassium, nor lactate of
iron was secreted by the salivary glands, though they were all secreted
by the kidney. Iodide of iron, on the other hand, passed into the saliva.

When lithium citrate is injected into the blood, the spectrum of
lithium can be detected in the first drops of saliva secreted.^ And
methylene-blue also passes into the saliva, but it does not appear to do
so constantly. Sulphindigotate of soda, which is so readily secreted by
the liver and kidney, is not secreted by the salivary glands;^ after
injecting large amounts into the blood, a small quantity may be found
in the saliva, but there is no reason to believe that this is due to any
cause other than diffusion.

Effects of the Cranial and Sympathetic Nekves on the
Blood Flow.

The fundamental fact that the cranial nerve contains vaso-dilator
fil)res and the sympathetic vaso-constrictor fibres, has been already
mentioned. If any salivary gland be exposed, it will be seen to flush on

1 Pfliiger, Arch. f. d. gcs. Physiol., Bonn, 1868, Brl. i. S. 686.

- Gamgee, "Physiological Chemistry," vol. ii., from whom much of this paragraph
is taken.

" "Lecons de physiol. experimentale," 1856, Bd. ii.

"* On injecting a large quantity of dextrose into the blood, I have found sugar in the
saliva, and in quantity which is, I think, much too large to be accounted for by diffusion.

'^ Langley and Fletcher, Phil. Trans., London, 1889, vol. clxxx. p. 149.

•^ Eckhard, Pcitr. ::. Physiol. C. Ludwiy, z. s. 70, Gchurtst., Leipzig, 1887, S. 13.



EFFECTS OF NER VES ON THE BLOOD FLO W. 505

stimulating the cranial nerve, and to become pale on stimulating the
sympathetic.

The more detailed examination ^ of the blood flow through the gland
has been made almost exclusively on the submaxillary gland of the dog.
The blood flowing ordinarily from the vein is dark ; on stimulating the
chorda tympani, the blood flow increases rapidly for ten to twenty
seconds, and then slowly decreases to normal ; the blood itself becomes
arterial in colour. The degree of the increase naturally varies, the flow
may be five times as fast as the normal. In favourable cases the vein
pulsates, and when it is cut the blood issues in jets, somewhat as from
a small artery. Bernard gives the normal blood flow through the gland
as about 5 c.c. in a minute ; and this has been approximately the rate of
flow in my own experiments, in which anaesthetics were given. Von Frey
found — presumably in very large dogs — the rate of blood flow through
the gland to be much greater, about 12 c.c. in a minute. In v. Prey's
experiments, stimulation of the chorda for ten seconds caused the rate
of blood flow to be 3 to 7 c.c. in five seconds ; the effect rapidly decreased
on repeated stimulation ; the flow was diminished by curari.

There are no complete observations on the changes in the gases of the
blood as it passes through glands in rest and in activity, but some data are
given by Bernard."

According to Bidder,^ the maximal blood pressure in the vein,
as the result of stimulation of the chorda tympani, is 37 mm. of
mercury.

On stimulating the sympathetic the blood becomes darker, and flows
more and more slowly, the maximal effect being obtained in twenty to
thirty seconds.

It is doubtful whether the sympathetic completely stops the blood flow
in the normal submaxillary gland ; it does so at times in an experiment, but
this may be due to clotting occurring when the blood becomes slow. In the
parotid the effect of the nerve appears to be greater.

The latent period of both chorda and sympathetic varies from a
barely perceptible time to several seconds ; it depends upon the strength
of the stimulus, the number of previous stimulations, and other con-
ditions; but, generally speaking, the latent period is longer with the
chorda than with the sympathetic.

Both nerves have a rather long after-action. The maximal effect
remains for ten to fifteen seconds, and the original rate of blood flow
only recurs a minute or so after the end of the stimulation. The dura-
tion of the after-action depends, up to a certain limit, upon the duration
of the stimulus ; and it appears to be greater with the chorda tympani
than with the sympathetic. These points, however, have not received
much attention.

When both nerves are stimulated simultaneously with maximal
currents, the sympathetic gets the upper hand during the stimulation,

■* Bernard, Journ. de Vanat. ct physiol., etc., Paris, 1858, tome i. pp. 233, 649 (reprints
from Compt. rend. Acad. d. sc, Paris, of the same year) ; "Le9ons sur les propri^t(^3 physiol.,
etc.," 18f)9 ; v. Frey, Arb. a. d. physiol. Anst. zu Leipzig, 1877, Bd. xi. S. 89 ; Langley,
Journ. Physiol., Cambridge and London, 1889, vol. x. p. 316.

^ Cf. "La chaleur animale," 1876, p. 179.

'^Arch.f. Anat. u. Physiol. , Leipzig, 1866, S. 339.



5o6 THE SALIVARY GLANDS.

and anaemia of the gland is produced as if the sympathetic alone were
being stimulated. Von Frey, using brief stimuli — usually lasting about
ten seconds — observed that the after-action was that of the chorda
tympani, and in some cases the increase of blood flow after the stimula-
tion appeared to be as great as if the chorda alone had been stimu-
lated.

When, however, the sympathetic is stimulated with weak currents,
and the chorda tympani with strong currents, there is, within certain
limits, an algebraical summation of effects. And the constriction pro-
duced by a weak stimulation of the sympathetic may be more or less
annulled by a strong stimulation of the chorda.

Mutual Effects of the Ckanial and Sympathetic Nerves
UPON Secretion.

We have already mentioned, under the head of the augmented
secretion (p. 496), the effect on the sympathetic saliva of a previous
brief stimulation of the cerebral nerve.

When the chorda tympani and the sympathetic nerve in the cat
are stimulated simultaneously with minimal currents of not too long
duration, the amount of saliva ol)tained is greater than that which is
obtained from either nerve alone.^ In the dog the same effect may also
be seen ; at any rate, if the gland is in a state to allow the sympathetic
to produce an augmented secretion.

As the currents are increased in strength, the amount of the saliva
obtained by simultaneous stimulation becomes rapidly less and less in
excess of that obtained by stimulating the chorda alone. And with a
very moderate strength of sympathetic stimulation, the amount of saliva
obtained by simultaneous stimulation falls below, and it may be very
considerably below, that which is afforded by stunulation of the chorda
by itself. The secretion is rapid for five or ten seconds, and then
speedily becomes slow. The retarding effect of the sympathetic we may
reasonably attribute to the diminution in the blood supply to the
gland which it brings about.

In the parotid gland of the cat similar effects are seen on excitation
of the sympathetic and of Jacobson's nerve. The sympathetic nerve in
the dog has a very marked retarding action upon the flow of saliva pro-
duced by Jacobson's nerve from the parotid gland, and it may stop the
flow altogether (cf. also p. 498).

Prolonged stimulation of the sympathetic reduces the irritability of
the gland, so that, on subsequent stimulation of the chorda tympani, the
saliva only appears after a long latent period, and but gradually acquires
its normal rate of flow.

Czermak ^ was the first to call attention to the retarding action of the
sympathetic upon the chorda secretion. He stated that in the dog, the
sympathetic stopped the chorda secretion, and produced a condition of the
gland of such nature that it did not for some time respond to stimulation of
the chorda tympani. He referred the action to inhibitory fibres, which he
beheved to loe present in the sympathetic. Eckhard^ considered that the

' Langley, Journ. Phydol., Cambridge and London, 1878, vol. i. p. 102.
- Sitzungsb. d. Jc. Akad. d. JVissensch., "Wien, 1857, Bd. xxv. S. 3.
^ Bcitr, '~. Anat. u. Physiol. {Eckhard), Giesson, 1860, Bd. ii. S. 95.



CRANIAL AND SYMPATHETIC NERVES. 507

retarding effect of the sympathetic was clue to the secretion produced by it
being very thick and viscid, and in consequence blocking up the ducts.
Heidenhain ^ attributed the action of the sympathetic to the lack of oxygen
caused by the diminished blood supply.

The effects on the percentage composition of chorda saliva, caused by
first obtaining a considerable quantity of sympathetic saliva, and vice
versd, were noted by Heidenhain.'^ He found that protracted stimulation
of either nerve diminishes the percentage of organic substance in the
secretion subsequently obtained by stimulating the other nerve.

(a) Thus stimulation of sympathetic for two hours — 0'65 grm. of saliva
secreted, containing 5 '9 per cent, solids.

The chorda tympani was then stimulated for two hours.

Stimulation of sympathetic for about one and a quarter hours — ,0"54 grm.
saliva, containing 2 "4 per cent, of solids.

(&) Stimulation of the sympathetic for six hours reduced the percentage of
the chorda saliva from 2*4 to 1"0.

Since the organic substance in the saliva comes in the main at any
rate — entirely, so far as we know — from the substance stored up in the
gland-cells, the facts given by Heidenhain show that the secretion
obtained from the two nerves arises in part at least from the same gland-
cells.

On microscopic examination of the submaxillary gland of the dog,
after several hours' excitation, either of the chorda tympani or of the
sympathetic, the alveoli are found to be changed to a very unequal degree, a
few having still the ordinary resting characters. This renders it probable that
the secreting fibres are not equally distributed to all the alveoli.

Since the sympathetic saliva contains a higher percentage of organic
substance than chorda saliva, we should expect that simultaneous stimu-
lation of the sympathetic and of the chorda tympani would give a saliva
containing a less percentage of organic substance than sympathetic
saliva, and a greater percentage than chorda saliva ; and this is the
case.

Heidenhain has shown that the chorda saliva which is obtained
shortly after stimulating the sympathetic has a higher percentage of
organic substance than that obtained before such stimulation. The
saliva, however, soon becomes normal, usually after 2 to 3 c.c. have
been secreted. The after-effect of sympathetic stimulation is com-
parable to the after-action caused by strong stimulation of the chorda
tympani, of which we have already spoken (p. 505).

We have dealt chiefly with the submaxillary gland, but the mutual
relations of the cranial and sympathetic nerves are essentially the same
in other salivary glands, including the parotid of the dog, in wdiich the
sympathetic nerve by itself commonly gives no flow of saliva.

The following results, taken from experiments by Heidenhain, Avill serve
to illustrate some points regarding the saliva secreted by the parotid gland
when both the sympathetic and Jacobson's nerve are stimulated.

^ Hermann's "Handbuch," Bd. v. S. 46.

" Stud. d. 2^^iysiol. Inst, zu Breslau, Leipzig, 1868, S. 71.



5o8



THE SALIVAR Y GLANDS.
Experiment 1. — Tlie Parotid Gland of the Dog.'^



Saliva obtained bj' Stimulating—


Duration of
Stimuli.


Amount of Saliva
collected.


Percentage of

Organic

Substance.


Percentage of

Salts.


Jacobson's nerve

Jacobson's nerve and the
sympathetic


18 min.
30 min.


3 "11 grms.
3-63 grms.


0-76
1-41


0-26
0-32



Experiment 2. — The Parotid Gland of the Rahhit.^

In this experiment pilocarpine was injected, and a sample of the saliva
collected. The cervical sympathetic was then stimulated ; during the stimula-
tion the secretion became slower until it stopped ; on its cessation the stimula-
tion Avas also stopped. After a short time the floAV began again ; when about
three drops had been secreted the sympathetic was again stimulated, and so
on, till a second sample of saliva Avas collected.



Saliva obtained from


Rate of Secre-
tion per Minute.


Percentage of

Organic

Substance.


Percentage of
Salts.


Pilocarpine .

Pilocarpine and sympa-
thetic stimulation


0-22 c.C.
0-062 C.C.


0-39
3-62


0-85
0-75



Effect of Variations in the Amount and Quality of the Blood
SUPPLIED to a Gland, upon the Amount and Pekcentage
Composition of the Saliva Secreted.

In order to form a satisfactory theory of the action of secretory
nerves, it is of the greatest importance to know how far variations in
the amomit and character of the blood flowing through the gland affect
the amount and character of the saliva. Our information on this point
is unfortunately still vague in many respects.

Certain broad facts can be readily observed by compressing the
carotid artery on one side, after tying the carotid artery on the other
side, and the subclavian arteries on both. The gland-veins are cut, so
that the amount of blood flowing through the gland can be roughly
determined; and the chorda tympani is stimulated during different
degrees of compression of the carotid.

When the carotid is compressed to a moderate extent, the chorda on
stimulation will not cause so much increase in the blood flow tlirough
the gland as it otherwise would, but it will nevertheless cause a con-
siderable increase, and the blood will issue from the vein of an arterial
colour. In such case, according to Heidenhain,^ the amount of saliva
obtained by a given stimulus will be of normal amount.

^ Heidenhain, Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xvii. S. 31.

^ Heidenhain, op. cit., S. 40.

^ Heidenhain {Stud. d. i^hysiol. Inst, zu Brcslau, Leipzig, S. 98) appears to refer to an
increase of blood flow above tliat occurring with partially compressed carotid, and not to an
increase above the normal blood flow.



EFFECT OF VARIATIONS IN THE BLOOD SUPPLY. 509

At a certain further stage of compression of the carotid, stimulation
of the chorda will still cause an increase of blood flow from the gland,
but the blood issuing from it, instead of being of an arterial colour, will
be of a venous colour. In this case Heidenhain finds that the amount
of saliva obtained by a given stimulus will be less than normal.

When the artery is so far compressed that little blood flows through
the gland, and the chorda causes no increase in it, there is naturally a
great decrease in the amount of saliva obtained by a given stimulus.
If the stimulus last about a minute only, the decrease is in fact nearly
as great as if the blood supply be entirely cut off. On allowing the
blood to flow again through the gland, the chorda saliva does not at
once attain its normal amount. Brief closure of the artery causes more
or less protracted diminution in the efficiency of the chorda; it may be
noted that the vaso-dilator effect of the chorda recovers more quickly
than its secretory effect.

The following example, taken from Heidenhain,^ may be given to illustrate
some of the points mentioned above : — Dog, arteries to head tied, except left



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 72 of 147)