Copyright
E. A. (Edward Albert) Sharpey-Schäfer.

Text-book of physiology; (Volume v.1) online

. (page 74 of 147)
Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 74 of 147)
Font size
QR-code for this ebook


The maximum difference found was 1°'6 C, the temperature of the saliva
in this case being 41°"2 C, the rate of secretion 0"5 c.c. in 5"5 seconds.
Ludwug gives also three experiments upon the respective temperatures of
the blood in the carotid artery, of the blood issuing from the gland vein,
and of the saliva. As a rule, the temperature of the v^enous blood was
below that of the carotid blood, but occasionally it w^as slightly greater
than that of carotid blood or of saliva. For example, in one case the
temperature of the blood in the carotid was 39°"1 C., that of the saliva
39°'3 C, and that of the venous blood 39°-4C.

The proof of an appreciable formation of heat during secretion
appeared complete when Heidenhain 3 oljserved by the thermo-electric
method that the temperature of the gland was often higher than that
of the carotid blood, the difference in favour of the gland being still
greater on stimulation of the sympathetic ; and when Morat,* by the
same method, obtained a rise of temperature in the submaxillary gland
of the dog, on stimulating the sympathetic both after bleeding the
animal to death and during temporary ligature of the carotid, sub-
clavian, and vertebral arteries.

Bernard ■' plunged one thermo-electric junction needle in each gland, and
found that stimulation of the chorda tympani caused a rise of temperature, and

'^ Sitzungsh. d. k. Akad. d. JVisscnsch., Wien, 1857, Bd. xxv. S. 684; reprinted in
Ztschr.f. rat. Med., 1858, N. F., Bd. ii. S. 361.

2 Wien. med. JFdmschr., 1860, S. 433 and 449.

3 SHul. d. physiol. Inst, zu Brcsluu, Leipzig, 1868, Heft 4, S. 110.
^ Arch, de 'physiol. norm, etpath., Paris, 1893, p. 285.

^ "La chaleur auinjale," Paris, 1876, p. 325.



ELECTRICAL CHANGES LN TLLE GLANDS. 517

stimulation of tlie sympathetic caused a fall of temperature in the gland of the
same side. He concluded that calorific nerve-fibres are present in the chorda
tympani, and frigorific nerve-fibres in the sympathetic ; but there is nothing
in the account to shoAV that the results were not due simply to a variation in
the blood supply.

These results till recently passed unquestioned. But Bayliss and
Hill/ on testing them, both 1 )y the thermo-electric and the thermometric
methods, never found the chorda saliva to be warmer than the arterial
blood. Their experiments differed in some points of method from
Ludwig's. On one of these they consider the difference in result de-
pends. The thermo-electric junction or the thermometer was pushed up
the femoral artery into the aorta, so that it was exposed to the full
current of blood. Bayliss and Hill consider that in Ludwig's experiment
the temperature observed was less than the real temperature of arterial
blood, so that, on stimulating the chorda tympani, the saliva secreted,
though of a higher temperature than that recorded for the blood, was
not of a higher temperature than that of the blood actually supplied to
the gland.^ And they came to the conclusion that no formation of heat
in the submaxillary gland can be determined directly by any known
method of measuring variations in temperature.

Supposing for a moment that this conclusion is correct, it does not
of course mean that no heat is formed in the gland during secretioji, but
simply that the heat — undoubtedly set free by the chemical changes — is
insufficient to cause an appreciable rise of temperature in the considerable
mass made up of the saliva, the gland, and the blood flow^ing through the
gland. But the main question can hardly be regarded as settled. For
the tissues in the neighbourhood of the gland artery and of the duct are
— at any rate, after placing a cannula in the duct and preparing the
chorda tympani — at a lower temperature than the aortic blood. So that
both the l)lood to the gland and the saliva secreted tend to become
cooled. And thus it would be possible for the recorded temperature of
the saliva to be less than that of aortic blood, although the temperature
of the saliva secreted were higher than that of the blood supplied to the
gland.

Electrical Changes in the Salivaey Glands.

The electrical currents of the salivary glands of the dog and cat
have been made the subject of observation by Bayliss and Bradford,^ and
by Bradford.''^ In such experiments, one non-polarisable electrode is
placed upon the outer convex surface of the gland, and the other upon
the gland close to the hilus. It is convenient to use Hermann's nomen-
clature for the currents which may be observed. When the outer
surface of the gland is positive to the hilus, so that the direction of the
current in the galvanometer circuit is towards the hilus, and in the

' Journ. Physiol., Cambridge and London, 1894, vol. xvi. p. 351.

- It may be mentioned that the blood temperatures recorded by Bayliss and Hill are in
nearly all cases less than those recorded by Ludwig, but no definite conclusion can be
drawn from this.

^ Proc. Roy. Sac. London, 1886, No. 243, p. 203 ; Internal. Journ. Anat. and Hislol.,
1887, vol. iv. The ingoing current of the skin of the frog was discovered by dn Bois Rey-
mond in 1857. He attributed it to the glands present in the skin (cf. " Untersuch. il.
tliierische Elektricitat," 1860, Bd. ii.

* Journ. Physiol., Cambridge and London, 1887, vol. viii. p. 86.



5i8 THE SALIVARY GLANDS.

gland itself from the gland-cells to the surrounding tissue — the current
is an ingoing current. When the outer surface of the gland is negative
to the hilus, so that the direction of the current in the galvanometer
circuit is from the hilus to the outer surface, and in the gland itself
from the gland-cells towards the duct, the current is outgoing. The
outgoing current, then, is one in the direction of the flow of the saliva
secreted.

The current of rest may be either outgoing or ingoing. It is
usually outgoing in the submaxillary gland of the dog, and usually ingoing
in the submaxillary gland of the cat. The causes of the difference of
direction have not been determined.

Any stimulation of nerves which causes a rapid flow of saliva will
cause a strong outgoing current. When the flow of saliva is slight, the
current, as a rule, is either diphasic, first outgoing and then ingoing, or
ingoing only. Thus in the submaxillary or parotid gland of the dog,
stimulation of the cranial nerve causes an outgoing current, and stimula-
tion of the sympathetic, provided the secretion be slight, causes an
ingoing current. The ingoing current begins less quickly and is less
strong than the outi^oino; current.

In the submaxillary gland of the dog, the current of rest is said to vary
from 1-500 to 1-10 of a volt. The outgoing current, caused by stimulating the
chorda tympani, begins about 0"37 seconds after the beginning of the stimu-
lation, and before saliva appears in the duct ; it reaches its maximum before
the maximum rate of secretion is attained. It may undergo temporary
diminution or reversal, indicating the development of an ingoing current.
The ingoing current, caused by stimulating the sympathetic, begins two to
three seconds after the beginning of the stimulation, and only slowly attains
its maximum.

In the submaxillary gland of the cat, stimulation, either of the chorda or
of the sympathetic, causes, in most cases, first an outgoing and then an ingoing
current.

Atropine annuls the effect of nerve stimulation, except perhaps in
the case of the sympathetic of the dog ; here the mgoing current pro-
duced by stimulation is much reduced, but it is not clear that it is com-
pletely abolished even by 100 mgrms. of atropine. Atropine annuls the
outgoing current of stimulation before the ingoing. The amount of
atropine required to abolish the outgoing current of stimulation is approxi-
mately that required to render the flow of saliva very slight. The
amount of atropine required to abolish the ingoing current of stimulation
is approximately that required to paralyse completely the secretory
activity of the nerve stimulated (cf. p. 512).

Bradford attributes the ingoing current to " changes in the gland
cells, leading to the elaboration of the organic constituents of the saliva,"
these being caused by the action of Heidenhain's trophic fibres, and
thinks that the outgoing current is probably due " either to the passage
of the fluid part of the secretion through the walls of the alveoli, or to
the changes in the gland structures, that follow the excitation of a
secretory nerve and precede the gland flow."

Most of the facts could be accounted for by supposing that the outgoing
current is due to physical causes, namely, due to the passage of fluid through the
gland-cells ; and that the ingoing current is due to chemical causes, namely, the
metabolic changes in the gland-cells, but the questions involved are too com-



SE CTION OF GLAND ULAR NER VES. 5 1 9

plex to allow a definite conclusion to be arrived at. In any adequate discussion
of the matter, the facts regarding the production of electric currents in other
parts of the body, and especially in the skin and mucous membrane, would
have to be taken into account. One or two points only we can mention here.
In the skin and mucous membranes of the frog and other animals investigated,
there is generally an ingoing electric current, which is increased by weak
stimulation. Hermann ^ considers both currents to be due to an "apobiotic"
change in the protoplasm. By " apobiotic " is meant any change which
diminishes the vital energy of a part of the protoplasm, compared with the
rest ; such as is produced by stimulation, the act of dying, the change of proto-
plasm to mucin or to keratin, and so forth. Parts undergoing apobiotic
change are negative to the rest of the protoplasm. Thus, in a mucous cell,
the inner mucous portion of the cell becomes negative to the outer proto-
plasmic part, and a current is then set up, which passes in the galvanometer
from capsule to hilus, and in the gland from mucous to protoplasmic portion,
i.e. there is an ingoing current. As to the outgoing current, Hermann is
inclined to consider it as a simple diminution (negative variation) of the
normal ingoing or secretory current ; whilst Biedermann advocates the view
that the outgoing current is due to anabolic (assimilatory) processes in the
gland-cells.

Section of Glandular Nerves. The Paralytic Secretion.

Claude Bernard ^ was the first to make observations upon the effect
of section of glandular nerves. He found that section of the chorda
tympani in the dog caused the submaxillary gland in Uno or three days
to enter into a state of slow continuous secretion. The slow flow of
saliva continued for five to six weeks, and then stopped. During this
time the gland itself diminished more and more in size.

Since the secretion is the result of the section of nerve-fibres, it has
been called the " paralytic secretion." Claude Bernard attributed the
secretion to the complete removal of nervous impulses. Thus the flow
of saliva did not begin for two or three days, because the terminations
of the chorda tympani in the gland required two or three days to
degenerate completely. It stopped in five to six weeks, because then,
he thought, the chorda fibres had regenerated.

The question was taken up a few years later by Heidenhain.^ In
order to exclude the possibility of the paralytic secretion being caused
by irritation of the duct or gland, he cut the chorda tympani in the
tympanic cavity. The secretion occurred in the same way as when the
nerve was cut peripherally of the ganglion, then called the submaxillary
ganglion (cf. above, p. 481). It began in twenty-four hours at least,
i.e. considerably earlier than the time given by Bernard. It was watery,
and contained very little mucin ; it contained many leucocytes (amoe-
boide Korperchen), and was in consequence somewhat cloudy. The
secretion was at first very slow, but gradually increased in rapidity, so
that in about a week a large drop might be secreted every twenty
minutes. After three weeks it diminished markedly. The gland itself,
as its size diminished, became of a yellowish tint, and waxy appearance.^

The time taken by the peripheral ends of the cut chorda tympani

1 Arch. f. d. ges. Physiol., Boun, 1894, Bd. Iviii. S. 246. References to much of the
earlier work will be found in this paper.

^ Journ. de Vanat. et ]ihysiol., etc., Paris, 1864, tome i. p. 507.
" Stud. d. ■physiol. Inst, zu Breslau, Leipzig, 1868, Heft 4, p. 73.



520 THE SALIVAR Y GLANDS.

fibres to degenerate is not quite accurately known. Heidenhain states
that in the dog, stimulation of the chorda causes a secretion three to four
days after its section, and implies that later than this the nerve has no
effect.^ In an experiment on the cat, I ^ obtained a copious secretion by
stimulating the cut end of the chorda three days after section ; a secre-
tion too copious, it seemed to me, to be attributed to the nerve-cells
which sometimes occur in the region stimulated. But Bradford,^ three
days after section of the chordo-lingual nerve near the pterygoid muscle,
obtained no secretion from stimulation of the nerve up to the point
where the chorda tympani leaves the lingual. In the dog he found no
efiect five days after section, but no experiment was made at an earlier
date. It appears, then, that the time required for a loss of irritability
of the cut chorda tympani in the cat and dog lies somewhere between
three and five days.

Notwithstanding the early loss of irritaljility of the chorda tympani
after section, stimulation of its nerve-strands near the gland will in the
cat still cause secretion. In this way I obtained a fairly rapid secretion
thirteen days after section of the nerve, and a slight secretion in another
experiment forty-two days after section of the nerve. And Bradford
obtained secretion from the chorda tympani in the cat up to eleven days
after section of the chordo-lingual. In his experiments he sometimes
obtained a secretion by stimulating the chorda immediately after it had
left the lingual nerve, but sometimes only when the electrodes were
shifted farther towards the gland. In the dog, five or more days after
section, he obtained no secretion by stimulating the chorda in any part
of its course.

Vulpian ^ noticed in the dog, that a fortnight after section of the
chorda tympani, injection of extract of jaborandi into a vein gave rise to
a secretion, though less than normal. Extirpation of the superior
cervical ganglion at the time of section did not affect the result. In
the cat, I found that thirteen days after section of the chorda, venous
injection of a few mgrms. of pilocarpine caused a copious secretion,
and that forty-two days after section of the nerve, pilocarpine still caused
a secretion, though distinctly less than on the opposite side.

These experiments, taken together with those already given on the
action of nicotine (cf. p. 515), and with our general knowledge of the
relation of visceral nerve-fibres to nerve-cells, show that, on section of
the chorda tympani, its nerve-fibres degenerate in three to five days up
to the peripheral nerve-cells. The nerve-cells are placed chiefly in the
gland itself — more so in the dog than in the cat. And there can be
little doubt that the variations oToserved as the result of stimulating the
peripheral portions of the chorda depend in the main upon variations in
the position of the peripheral ganglia. In some animals, postganglionic
fibres are stimulated when the electrodes are placed on the strands
outside the gland ; in other animals, tliis only occurs when the electrodes
are placed in the hilus. As the gland diminishes in size it naturally
gives a less copious secretion luider the influence of pilocarpine.

1 Heidenhain (Hermann's "Handbuch," 1880, Bd. vi. S. 88) states that, altlionyh there
was secretion, there was no increased flow of blood.

- Journ. FhysioL, Cambridge and London, 1885, vol. vi. p. 71.

= Ibid., 1888, vol. ix. p. 304.

•* Covipt. rend. Acad. d. sc, Paris, 1878, tome Ixxxvii. p. 350. Before this, Prevost had
stated that muscarine causes secretion after degeneration of the chorda tN'nipani ; cf. Arch,
de physiol. norm. e.tpcUh., Paris, 1874, p. 719,"note.



THE FARAL YTIC SE CUE TION. ■ 521

The peripheral nerve-cells^ in connection witli tlie gland may be
spoken of as a local nerve-centre. This local centre is capable of
exciting the gland-cells to activity long after the chorda tynipani, which
normally conveys impulses to it from the central nerve-centre, has
degenerated.

Heidenhain suggested that the paralytic secretion might be due to a
stimulation of the gland-cells by the decomposition ])roducts of the
stagnating saliva. He oliserved that if the duct were clamped for aljout
a day, a slow secretion of watery saliva ensued. The cases, however, are
hardly comparable, inasmuch as, whilst the duct is closed, secretion is
formed which partly distends the alveoli and partly is forced out of the
ducts and lumina, and bathes all the tissues of the gland.

A final explanation can hardly yet be given, but some observations
made on the cat lead me to think that the secretion is the result of
nervous stimuli. In the cat the paralytic secretion is much diminished
and even stopped by excess of chloroform and by apnoea ; and is
increased markedly by dyspnoea ; the dyspnoeic flow takes place more
readily than on the opposite side, and, so far as can be judged, more
readily than in a normal gland. These residts indicate that the
paralytic secretion is due chiefly, at any rate, to a slight continuous
excitation of the local nerve mechanism.

Heidenhain found that the paralytic secretion also occurred in the dog,
when the superior cervical ganglion was excised at the time of section of
the chorda. In this case the secretion is due wholly to local changes.
In the early stage of secretion in the cat, three days after section of the
chorda alone, I noticed that section of the cervical sympathetic very
much diminished or even stopped both the paralytic secretion and the
dyspnoeic secretion, although, in the later stages, section of the cervical
sympathetic had little or no effect. Probably, then, if the sympathetic
is intact, the secretion which occurs in tlie first few days after section of
the chorda is largely due to impulses travelling down the sympathetic
from the central nervous system.

The loss of weight which occurs in the submaxillary and the sub-
lingual glands, after section of the chorda tympani, amounts in a few
weeks to one-third to one-half of the original weight of the glands.
Bradford has shown that section of Jacobson's nerve causes a similar
loss of weight in the parotid gland ^ of the cat. Whether complete
atrophy takes place, and if so what time it requires, there is no evidence
to show.

In the submaxillary gland, and no doubt in the others also, the loss
of weight is due to a loss of cell substance by the individual cells. And
this loss is simply an instance of the gradual atrophy which occurs in
tissues in the absence of functional activity. The persistent slight
activity, of which the paralytic secretion is the sign, is quite insufficient
to replace the normal exercise of function.

In the dog, according to Heidenhain, the paralytic gland contains a
number of alveoli, presenting the appearance of the alveoli of an active
gland. In my experiments, both on the dog and cat, the gland-cells were
undoubtedly in the resting state. In the cat the saliva obtained by

^ Six weeks after section of tlie chorda in the cat, when the submaxillary gland had lost
one-third to one-half of its weight, the nerve-cells in the alcohol-hardened gland presented
no certain difference from the nerve-cells of the gland of the opposite side.

^ Bradford did not observe a paralytic secretion from the paiotid.



52 2 . THE SALIVARY GLANDS.

stimulating the postganglionic chorda fibres, and by injecting pilo-
carpine, was distinctly viscid, and more viscid than normal. The alveoli
mentioned by Heidenhain were, I am inclined to think, the demilunes
which a decrease in the size of the mucous cells inevitably brings into
prominence, notwithstanding an actual decrease in the size of the
individual demilune cells.

Stimulation of the cervical sympathetic, during the progress of the
paralytic secretion, has practically its normal action both in the dog and
the cat. In the dog, it gives, when stimulated after a sufficient interval
of rest, a brief quick flow of watery saliva, corresponding with the
augmented secretion, and after this a slow slight secretion even thicker
than usual. If the stimulus be prolonged, there is a long pause in the
paralytic secretion, due partly to anaemia of the gland, and partly to the
resistance offered to the flow by the thick saHva in the lumina and
ducts. In the cat, the sympathetic produces secretion in the usual way
and of the usual kind ; and unless the stimulation be too prolonged, the
paralytic secretion slowly creeps on in the intervals between the several
stimulations.

Heidenhain noticed in the dog that section of the chorda tympani on
one side caused a slight continuous secretion from the submaxillary
gland of the opposite side. The occurrence of such a secretion I con-
firmed in the cat. It is convenient to have a name for this secretion,
and I have called it the antiparalytic, or, more briefly, the antilytic
secretion. In my experiments the antilytic secretion was stopped by
apncea and by excess of chloroform. Dyspnoea caused a secretion
apparently greater than normal, though less than on the paralytic side.
No certain antilytic secretion was observed either thirteen or forty-two
days after section of the chorda. In its early stage, three days after
section of the opposite chorda, it was diminished by cutting the chorda
of the same side, and abolished by cutting the sympathetic also. So far,
then, as regards the cat, there is some ground for thinking that the anti-
lytic secretion is transitory and due to impulses set up in the central
nervous system.

Section of the chorda tympani probably leads to slow changes in the nerve-
cells of the secretory centre which are connected with the chorda fibres ;
these changes might make the central nerve-cells more irritable, so that they
passed into a condition of continuous slight activity, thus producing the anti-
lytic secretion. Or the antilytic secretion might, as suggested by Bradford, be
simply a reflex from the tissues injured during the section of the chorda.

According to Heidenhain, the antilytic secretion in the dog continues after
section of both chorda tympani and sympathetic nerves. As it is difficult to
see why the local mechanism should be so easily thrown out of gear, it is best
to wait for further observations on the matter.

Little is known as to the time taken for the chorda tympani fibres to
regenerate. In a puppy, I obtained, three months after section of the chorda
tympani, a secretion much as usual, on stimulating either the nerve which had
been cut or the chordodingual, so that presumably regeneration is fairly com-
plete in three months.

Section of the cervical symiKtthctlc'^ has no observable permanent effect
upon the gland, and it causes no paralytic secretion. The blood vessels
for a time dilate, but this soon passes off". The nerve soon loses its

^ Cf. Langley, o}). cit., and Bradford, op. cit.



REFLEX ACTION OF PERIPHERAL GANGLIA. 523

irritability ; in the cat, according to Bradford, it gives no secretion three
days after section.

Stimulation of the ganglion will still cause secretion and pallor of
the gland for several weeks after section of the nerve, and possibly
indefinitely.

Excision of the, superior cervical ganglion has also no certain effect
upon the salivary glands, and does not give rise to a secretion. In the
rabbit I could see no decrease in the size of the submaxillary glands,
or alteration in their histological appearance, nine, sixteen, and twenty-
three days respectively after removal of the ganglion, nor in a case in
which the ganglion had been removed five years previously by Dr. Pye-
Smith. The chorda tympani still causes secretion and flushing of the
gland, though the flushing is apparently less than normal. Bradford
removed the superior cervical ganglion in the cat. He found no atrophy
of the gland up to seven weeks after the operation ; indeed, in his cases
both the submaxillary and the parotid glands were somewhat heavier
on the operated than on the sound side. Eemoval of the ganglion
causes the sympathetic filaments on the gland artery to degenerate, the
loss of irritability being fairly rapid ; thus, three days after the operation,



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 74 of 147)