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beyond that of the taking up of oxygen and the giving off of carbonic
acid ? There is no experimental evidence to show whether the amount of
oxygen taken up by the gland cells is so much in excess of the carbonic
acid given off, that an increase in the weight of the gland takes place ;
but this is on general grounds probable enough, to prevent us from
attributing offhand any increase in weight which may occur in a gland
during rest to its cells having taken from the lymph proteid or substance
other than oxygen.

We may take first the evidence that glands increase in weight
during rest. Obviously this is proved, if it can be proved that there is
a decrease in weight during secretion.

Heidenhain stimulated the chorda tympani on one side in a dog, and,
after obtaining a considerable amount of saliva, killed the animal by
bleeding it, separated the glands on the two sides from their capsules,
and as far as possible from connective tissue, and then weighed them.
He found that the active gland weighed less than the resting gland.

^ Langley, Journ. Physiol., Cam bridgfi and London, vol. ii. p. 261 ; Internal. Monatschr.
f. Anat. u. HiHfoL, 1884, vol. i. p. 69 ; Proc. Roy. Soc. London, 1886, vol. xi. p. 362.

2 Heidenhain, Arch. f. d. ges. Phyaiol., Bonn, 1878, Bd. xvii. S. 43 ; Hermann's
"Handbuch," 1883 ; Lavdowsky, Arch. f. mikr. Anat., Bonn, 1877, Bd. xiii. S. 335.

^ It is perhaps hardly worth while to defend the use of the word "resting" for a gland
which for some time has secreted but little, and the use of the word "active " for a gland
which for some time has been secreting more or less copiously. The words lead to no
ambiguity, and the objections to them appear to me purely pedantic. "Active" and
"resting," applied to any living tissue, are essentially relative terms ; it can hardly be
doubted that there is greater chemical change when secretion is going on than when it is not.



CHANGES DURING SECRETION



487



Three experiments were made ; the chorda tympani was stimulated on
the left side.





Amount of Saliva
obtained.


Weight of Active
Gland.


Weight of Resting
Gland.


Experiment 1 . .

2 . .

3 . .


55 c.c.

75 c.c.

220 c.c.


5 '04 grms.
5-42 ,,
5-91 ,,


5 '06 grms.
6-86 ,,
6'36 ,,



In these experiments the left gland was the one that was caused to
secrete, and there is some reason to think that the left gland is normally
heavier than the right, for Bidder found this to be the case in eleven
cases, and Heidenhain in two.^ Pawlow,^ however, noticed no appre-
ciable difference in the amount of nitrogen contained by ten right
and by ten left submaxillary glands of the dog. But so long as it is not
shown that the right gland may be normally heavier than the left, we
may fairly conclude that there is a loss of weight by the gland during
secretion and a gain of weight during rest.

The question may be approached from another side. Microscopical
examination shows decisively that during secretion the gland cells
become smaller; they must then, taken together, decrease in weight
unless the percentage of solids in them increases. But, according to
Heidenhain, the percentage does not increase during secretion ; on the
contrary, it decreases. Thus, in one experiment upon a dog, in which
about 220 c.c. of saliva were obtained by stimulating the chorda tympani,
the percentage of solids in the resting gland was 28"3 per cent., and in
the stimulated gland it was only 21-3 per cent., so that there were 7 per
cent, less solids on the stimulated side.

This, it must be remembered, applies to the gland as a whole. In con-
cluding that there is a decrease in the percentage of solids in the actual gland
cells, we assume that the percentage composition of the glands on the two sides
is approximately the same, that there is no appreciable difference in the amount
of blood and lymph upon the two sides, and that the connective tissues in the
gland are too small in amount or too constant in composition to affect the result ;
these assumptions, however, appear to be justifiable.

The other experiments made by Heidenhain ^ were as follows: —

1. The left chorda tympani was stimulated and 75 c.c. of saliva obtained.
The right submaxillary gland contained 23 per cent, of solids, the left gland
18 "6 per cent. — a decrease of 4*4 per cent.

2. The left chorda tympani was stimulated and 55 c.c. of saliva obtained.
The right submaxillary gland contained 24 per cent, of solids, the left gland
21 '5 per cent. — a decrease of 3-5 per cent.

Heidenhain found a slight decrease also in the percentage of solids on
stimulating the cervical sympathetic* The time of stimulation is given, but
not the amount of saliva obtained.



^ Op. cit., p. 57.

2 CentralU.f. Physiol., Leipzig u. Wien, 1888, S. 137.

^ Stud. d. 2)hysiol. Inst, zio Breslau, Leipzig, 1868, Heft 4, S. 55.

* Op. cit., p. 66.



488 THE SALIVARY GLANDS.

1, Sympathetic stimulated for two and a half hours. The resting gland
had 25 per cent, of solids, the stimulated gland 23"6 per cent.

2. Sympathetic stimulated for five and a half hours. The resting gland
had 25 per cent, of solids, the stimulated gland 24*4 per cent.

We may conclude, then, that during secretion the gland cells
decrease in weight, and therefore that they increase in weight during
rest. The increase in rest might be due, as we have said, to a taking up
of oxygen. But the observations of Pawlow,^ if they are well founded,
show that, whether an increase in weight due to oxygen combinations
occurs or not, there is during rest a not inconsiderable increase in the
nitrogen of the glands, and this can hardly be due to anything else than
an absorption of proteids. Pawlow estimated by Kjeldahl's method the
amount of nitrogen in the resting submaxillary gland of the dog on the
one hand, and in the stimulated gland and in the saliva secreted by it
on the other hand. He obtained saliva by stimulating the central end of
the sciatic for one and a half to five hours. In ten (right) stimulated
glands he found 1-872 grms. nitrogen. In the ten (left) non-stimulated
glands he found 218 grms. of nitrogen. Assuming, then, that the glands
had the same amount of nitrogen to start with, the stimulated
glands had lost during secretion about 4- of their nitrogen -holding
substance. In the saliva secreted he found 0-416 grms. of nitrogen,
so that presumably the glands had taken up during secretion about
0-1 grm. of nitrogen; this is about ^Y o^ the total amount. The
numerical results are not such as we should expect from the micro-
scopical appearances of the gland cells, and it is desirable that the
experiments should be repeated.

The general characters of the cells of the lobular ducts suggest that
they are not simply the lining cells of a conducting tube, but are rather
active constituents of the gland, concerned either with adding to the
saliva as it passes by them, or with subtracting from it. There is not,
however, any clear evidence on the matter. It is true that when a con-
siderable amount of methylene-blue is injected into the blood, and the
glands are excited to secrete, small deep blue particles may be found in
the duct cells as in the alveolar cells, but methylene-blue is so readily
taken up by many tissues that little trust can be placed on this as show-
ing a secretory function. The cells of the lobular ducts contain small
granules in their outer portion,^ and, according to Mislawsky and
Smirnow,^ these granules decrease during secretion, but it does not
appear to me certain that the changes described by these authors are not
due to conditions other than secretory activity. Merkel * observed that
the cells with striated epithelium, i.e. most of the lobular duct cells of
the submaxillary and parotid glands, stained a deep brown when treated
with pyrogallic acid in the presence of oxygen. He considered that the
stain was due to the presence of calcium salts in the cells. This
naturally suggested that the lobular ducts with striated epithelium might
secrete calcium salts. But Werther ^ has shown that the percentage of
calcium salts in the sublingual saliva of the dog is rather greater than in

1 Centralbl. f. Physiol., Leipzig u. Wien, 1S88, S. 137.

^ Langley, Journ. Physiol., Cambridge and Londou, 1889, vol. x. p. 433. "When the
granules of the duct cells swell up and become indistinct, the substance between them takes
on tlie characteristic striated appearance seen in hardened specimens.

'■''Arch./. Anat. u. Physiol., Leipzig, 1896, Physiol. Abth., S. 93.

■* " Die Speichelriihren," Leipzig, 1883.

^Arch.f. d. gcs. Physiol., Bonn, 1886, Bd. xxxviii. S. 293.



REFLEX SECRETION OF SALIVA. 489

submaxillary saliva. And it happens that the ducts with striated
epithelium are very scanty in the sublingual gland, whilst they are
numerous in the submaxillary gland.

Keflex Secketion of Saliva in ISTormal and in other
Conditions.

In man, more complete observations have been made on the flow
of saliva from the parotid than on that from the submaxillary gland,
since the duct of the parotid is sometimes accidentally injured, so that
the establishment of a parotid fistula becomes necessary. But some of
the conditions of flow from either gland may be readily observed, when
a cannula is simply placed in the opening of the duct of the gland into
the mouth.

In the dog, sheep, horse, and other animals, sometimes a permanent
fistula, and sometimes a temporary fistula, of one or more of the glands
is established. The observations have been made with and without the
administration of amesthetics.

Ordinarily, between meals, the large salivary glands — except the
parotid glands of ruminants — do not secrete. But as the mucous
membrane of the mouth is constantly kept moist, saliva must constantly
be formed by the smaller glands of the mucous membrane. In some
animals the amount of this secretion is very considerable ; thus in the
horse, during abstinence, 100 to 150 c.c. of saliva are, according to Colin,^
formed in an hour. Probably during sleep the amoimt diminishes.
There is little doubt that this secretion is produced reflexly by conditions
affecting the mucous membrane of the mouth, and a slight increase in
the strength of the stimuli probably sets in action the larger glands also.

In ruminants there are some peculiarities. The parotid gland se-
cretes continuously (Colin,^ Eckhard -). The secretion is most abundant
during feeding, rather less during rumination, and one-eighth to one-
fourth the rumination rate during rest.^ During rest, the submaxillary
glands secrete little or not at all, and it is a remarkable fact that
rumination does not, as a rule, cause any secretion from these glands,
although it increases the secretion from the parotid gland, and although
feeding causes a secretion from all the glands.

CoHn found in ruminants a slight continuous secretion from the sub-
maxillary and sublingual glands during rest. EUenberger and Hofmeister^
found none, but they noticed that there was occasionally a slight secretion
from the submaxillary gland during rumination, and a more copious secretion
during the act of drinking. According to these observers, there are occasional
short pauses in the parotid secretion during rest.

In ruminants, further, it has been said * that the secretion from the parotid
gland continues after section of all the nerves running to it. In the ox,
Moussu (1890) found that section of the buccal nerves diminished greatly,
but did not quite stop, the parotid secretion. Eckhard (1893) states that
section of these nerves does not affect the parotid secretion in the sheep ; he
found about \\ c.c. to be secreted in ten minutes, whether the nerves were
cut or no. The matter requires further investigation.

1 0:p. cit. " Ztschr.f. rat. Med., 1867, Bd. xxix. S. 74.

3 Arch.f. Anat. u. Physiol., Leipzig, 1887, PhysioL Abth., Supp.. Bd., S. 138.
•* CentralU. f. Physiol., Leipzig u. Wien, 1893, S. 305. Of. Schwann, Beitr. z. Anat.
u. Physiol. {Eckhard), Giessen, Bd. vii. S. 170.



490 THE SALIVARY GLANDS.

In man during hunger, the sight, smell, or idea of food is sufficient
to cause a secretion of saliva from all the salivary glands ; and
chewing insoluble substances has a similar, though apparently a less
effect.i

Secretion in this way is said not to occur in lower animals. Thus
Schiff- found in a dog with a parotid fistula, that no flow of parotid
saliva was caused by the sight or smell of the meat the animal was
endeavouring to obtain ; when it was induced to bite a piece of wood,
the meat still being in sight, there was slight secretion from the
submaxillary gland but none from the parotid, but on placing sapid
substances in the mouth there was at once a rapid secretion. And Colin
states that, after a parotid fistula has been established in a horse, and
when the animal is in a state of hunger, there is no secretion from the
parotid when the animal is offered, but not allowed to take, corn, nor
when it masticates oakum, although mastication of corn readily causes
a secretion.

Sapid substances taken into the mouth cause more or less secretion
from all the salivary glands. In man all substances are effective, and
drinking, wine for example, is sufficient.^ Acid placed on the tongue is
apparently the most effective stimulant among the sapid substances, but
there are not sufficient observations in man as to the amount of saliva
produced by other substances, to allow a satisfactory opinion to be formed
as to the relative effectiveness of salt, sweet, and bitter bodies. Masti-
cation considerably increases the flow of saliva, probably by l^ringing
the particles into better and more frequent contact with the mucous
membrane.

Chloroform and ether when inhaled cause secretion, by stimulating
the gustatory nerve endings, and possibly also the other nerve- endings in
the mucous membranes; if given by the trachea, they do not cause
secretion. Alcohol, ether, or chloroform, when mixed with water and
held in the mouth, cause a fairly free secretion of saliva.

In carnivora, so far as the experiments go, acids (vinegar, tartaric
acid) cause the most abundant secretion ; salts, either neutral or alka-
line, a less secretion, but still a faii'ly copious one ; bitter substances a
much less secretion, and sugar little or even none. With sapid sub-
stances in the mouth the secretion is increased by mastication.

Thus Bernard, '^ in one experiment on a dog, in which cannulse were placed
in the ducts of all three glands, obtained a copious secretion from vinegar, less
from sodium carbonate, still less from colocynth, and none from sugar or from
water. The relative effect on the several glands Avas practically the same with
all the substances.

Schiff^ obtained some secretion from the parotid fistula of a dog by
placing sugar on the base of the tongue, but none by placing it on the tip.

According to Colin,^ weak acids, salts, or aromatic substances placed on
the buccal mucous membrane give rise to no aj^preciable secretion from the
parotid of the horse during abstinence, and do not sensibly increase the con-

1 Colin and Prompt, 1874 (see Colin, "Traite de physiol. compar(5o," etc., 3rd edition,
p. 1), in the case of a c^irl with a parotid fistula, noticed that chewing a piece of ribbon
caused a secretion of only one drop of saliva in two minutes.

- " Lecons sur la physiologic de la digestion," 1867.

•"' Colin and Prompt (1874), case of parotid fistula (cf. supra).

■• " Lemons dc yihysiol. exper.," 18.56, tome ii. p. 82.

° " Lemons sur la physiol. de la digestion," 1867, tome i. p. 186.

^ Oj}. cit., p. 653.



REFLEX SECRETION OF SALIVA. 491

tinuous parotid secretion of ruminants ; but do nevertheless cause a secretion
from the submaxillary and sublingual glands. His statements, however, are not
quite consistent, and we may suppose that the difference is only one of degree.

In herbivora, mastication is performed alternately on the two sides,
the periods being usually one quarter to half an hour. In the horse, and
probably in other herbivorous animals, the secretion from the parotid is
much greater on the masticating than on the non-masticating side. In
the horse two to three times as much saliva is usually secreted on the
masticating as on the opposite side, but the ratio may be either greater
or less than this (Bernard, Colin). It seems reasonable to suppose that
this is due to the better contact of food with the mucous membrane of
that side of the mouth. According to Colin, however, there is no such
difference in the secretion of the submaxillary and sublingual glands.

The amount of saliva secreted varies with the nature of the food.
In man the data are not sufficient to form an estimate of any value,
either of the relative amount of saliva secreted from the several glands,
or of the total amount secreted in twenty-four hours. It is generally
supposed that the total amount exceeds a litre a day.^

Bernard ^ found that in the dog, when saliva was obtained reflexly,
the submaxillary gland secreted about twice as much as the parotid, and
about ten times as much as the sublingual. And these are approxi-
mately the relative amounts obtained by injecting pilocarpine. The
amounts secreted are roughly in proportion to the respective weights of
the glands.

In herbivora the volume of saliva secreted by the submaxillary and
sublingual glands does not correspond with their respective weights.
According to Colin, the parotid gland of the horse secretes fifteen to
twenty times the volume of saliva secreted by the submaxillary gland,
but is only about four times its weight. And in the ox the parotid
secretes four to five times as much saliva as the submaxillary gland,
though it is slightly less in weight (cf. Table, p. 477).

Colin estimates that in the horse the total quantity of saliva secreted
in a day is about 40 litres.

The total quantity of saliva may be estimated in two ways — (1) By com-
paring the weights of a certain amount of food before and after mastication
and swallowing, the food after mastication being collected from an oesophageal
fistula ; and (2) by noting in different experiments the quantity secreted by
each gland during a given period of feeding. Colin found, by the first method,
that a horse secreted 5000 to 6000 grms. of saliva in an hour, when fed with
hay, one-half of this when fed with grass, and one-third more than this when
fed with oats.

During digestion, according to Colin, the sidDmaxillary gland of one side
secretes 25 to 30 c.c. of saliva in fifteen minutes ; the parotid secretes 500 to
1000 (about) in fifteen minutes, if mastication takes place on this side.^

In the ox he estimates that during three hours' mastication, and five
hours' rumination, about 40 litres of saliva are secreted, and that 16 litres are
secreted during the sixteen hours of rest.

Electrical excitation of the central end of the lingual or of the glosso-
pharyngeal causes secretion from all the salivary glands. The secretion

^ Some data are given by Tuczek, Ztschr. f. Biol., Munchen, 1876, Bd. xii. S. 534.

^ " Lecons de physiol. exper.," 1856, tome ii. p. 82.

^ For other observations on this point, cf. Ellenberger and Hofmeister, ojj. cit., supra.



492 THE SALIVAR Y GLANDS.

is less copious than that obtained by placing acids in the mouth, and it
is more copious on the side stimulated than on the opposite side.

A special relation has also been said to exist between the state of
the mucous membrane of the stomach and the secretion of saliva. Thus
it has been said that a secretion of saliva is induced by the contact of
various substances with the gastric mucous membrane.^ This, however,
is not satisfactorily proved. Braun ^ observed a dog, in which a gastric
fistula had been established, and a cannula placed in Wharton's duct.
No secretion of saliva was caused by introducing into the stomach,
flesh, acetic acid, ether, nor by irritating the mucous membrane with a
sponge.

Stimulation of the central end of the vagus has rather variable
results on the submaxillary secretion of the dog. It usually causes
secretion after a long latent period, and the secretion may continue for
some time after the cessation of the stimulus. Oehl ^ obtained secretion
although the stimulation caused no vomiting or arrest of respiration ; the
secretion occurred from both glands, but was greater on the side stimu-
lated. Buff, as a rule, only obtained secretion when there was some
body movement.

Bernard noticed that a flow of saliva may 1je obtained by stimulating
the sciatic * and various other sensory nerves ; it may, indeed, be obtained
by stimulating any sensory nerve in the body. This reflex secretion is
abolished by deep anaesthesia ; whether it ceases coincidently with the
production of aucesthesia is, however, uncertain. Accordmg to Buff,^
the secretion does not occur in uncurarised animals, unless the stimulus
produces also a reflex body movement.

The gustatory reflex secretion is caused wholly by impulses passing
down the cranial secretory nerves. But a secretion may, in certain
cu-cumstances, be caused by impulses passing along the sympathetic
nerve ; for example, when the central end of a sensory nerve is stimu-
lated, the secretion, so far as is known, is always accompanied by a con-
striction of the blood vessels of the gland.

In man, cases sometimes occur in which there is a permanent absence
of secretion from the large salivary glands, and from the glands of the
mucous membrane of the mouth. Such cases are rarer in men than in
women. In women the loss of secretory power usually comes on after
middle life, and may be the result of an emotional shock. For some
time pilocarpine will still cause a secretion of saliva (Hadden), but
eventually it causes none, though it still causes sweating.^ The
absence of secretion is no doubt due to a derangement of the reflex
nervous mechanism, so that impulses passing up the afferent nerves no
longer give rise to efferent impulses. The lack of normal functional
activity probably causes a gradual atrophy of the glands, and a diminu-
tion of irritability of the nervous and glandular structures, so that
eventually pilocarpine — or the amount of it which can be given safely —
no longer produces a flow of saliva.

1 For an account of papers on the reflex secretion of saliva, cf. Bulf, Beitr. z. Anat. u.
Physiol. {Ecklmrd), Giesseu, 1888, Bd. xii. S. 3.

^ Ihid., 1876, Bd. vii. S. 44.

■' Covi23t. rend. Jcad. d. sc, Paris, 1864, tome ix. p. 336. Secretion on stinnilatiou of
the central end of tlic vagus was first observed by Bernard, 18.59.

■* Cf. also Owsjannikow and Tschiriew, Melanges hlol. Acad. imj). d. sc. de SL-Pcters-
bourg, 1872, tome viii. p. 6.51.

^ O]}. cit. '■ Hutchinson, cf. Hadden, Brain, London, 1889, vol. xi. p. 484.



THE DYSPNCEIC SECRETION. 493

The Dyspnceic Secretion.

At a certain stage of dyspncBa the saliva liows with considerable
rapidity from all the salivary glands. The time at which it begins and
its amount are dependent upon the degree of antiesthesia. In anaesthesia,
the secretion does not usually begin until the stage of expiratory convul-
sions. With a large excess of anaesthetics, the animal may be killed by
asphyxia without any secretion occurring, or with only a trifling amount.
When a copious secretion occurs it is due to impulses passing down the
cerebral nerve fibres, but some secretion may be obtained after section
of these nerve fibres. In such case there is also contraction of the
glandular arteries. Whether dyspncea is capable of producing a secre-
tion after section of the cerebral nerve and excision of the superior
cervical ganglion, has not been sufficiently investigated.

Stimulation of the Ceanial Nerve supplying a Salivary

Gland.

On some general features of the secretion. — A flow of saliva can
be obtained from any of the salivary glands by electrical, mechanical, or
chemical stimulation of the cranial secretory nerves. It need hardly be
said that the interrupted current is the most effective form of stimulus.
A very weak interrupted current, which cannot be felt on the tongue, is
sufficient to cause a secretion. Within certain limits the rate of flow of
the saliva increases with the strength of the stimuli, but strong currents
rapidly injure the nerve at the point of stimulation. Even with
moderate currents a very slight shifting of the electrodes on the nerve
usually causes a marked increase in the rate of secretion, a fact which it
is important to bear in mind in collecting for analysis different samples
of saliva, secreted under different conditions.



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 70 of 147)