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The flow of saliva with a moderate strength of current is very rapid ;
thus the submaxillary gland in the dog may secrete in five minutes an
amount of saliva weighing as much as the whole gland.

The nerve can be stimulated electrically for half an hour to an hour,
and probably with proper precautions very much longer, without the
flow of saliva ceasing. Pilocarpine in successive doses (cf. p. 513) will
cause a secretion for, so far as we know, an indefinite time.

In protracted electrical stimulation the maximum amount of saliva
is obtained by stimulating for short periods, with short intervals of rest ;
the stimulation being stopped each time as the secretion becomes slow.
In this way in ten to twelve hours about 250 c.c. of saliva can be
obtained from the submaxillary gland of the dog, and a half to two-
thirds of this amount from the parotid. The rate of flow gradually
diminishes during the progress of the experiment. With a given
strength of current, the maximum rate of secretion is produced with a
rate of interruption of about forty a second.^

According to Wedensky, rapid shocks, such as 100 to 250 a second, cause a
change in the nerve-endings, so that they soon cease to transmit nervous
impulses. His most striking experiment is the following : — Two pairs of
electrodes are placed on the chorda tympani, shocks of moderate rate are
passed through the lower, and of rapid rate through the upper; the secretion
1 Wedensky, Compt. rend. Acad. d. sc, Paris, 1892.



494 THE SALIVAR Y GLANDS.

soon becomes slow or stops altogether, but, on cutting off the rapid shocks
from the upper electrodes, the stimuli at the lower electrodes become again
effective, and the secretion starts once more. The results are similar to those
he obtains with motor nerves to skeletal muscle.

The real latent period of the gland cells cannot be accurately deter-
mined by any direct method, and in consequence it is customary to speak
of the interval between the moment of stimulating the nerve, and the
moment at which the movement of saliva occurs in the duct, as the
latent period. When the cranial nerve is stimulated with a weak
current, there is an obvious interval — usually two to four seconds —
between the moment of application of the stimulus and the appear-
ance of saliva in the cannula, and this is the case although the
secretion when it occurs is not scanty. When stronger currents are
used, and the secretion is copious, the latent period is much dimin-
ished. On the other hand, when the secretion is scanty, the latent
period is very much prolonged, whatever the strength of current ; thus,
after a small dose of atropine, it may be half a minute or even more.

The percentage of organic substance in saliva obtained from differ-
ent salivary glands varies considerably ; in each, as we shall see, it
varies in different circumstances, and in each it ma}' be small (0'2
to 0-5 per cent.). But, other things being equal, the submaxillary
saliva has usually a higher percentage of organic substance than
either the sublingual or the parotid saliva.

There is a curious difference in the percentage of salts found in
different salivas. In the dog the maximum percentage of salts in the
parotid saliva is about 0"68, in that of the submaxillary gland about
0-77, and in that of the sublingual gland about I'O.^ In the rabbit
the parotid saliva has a maximum percentage of about 0'85.^

After action of a strong stimulus.— Strong stimulation of the
cranial nerve alters the gland it supplies in such a way, that the
saliva secreted shortly afterwards has a higher percentage of solids
than it otherwise would have had.^ Thus, in the experiment quoted
on p. 501, the first weak stimulation of the chorda tympani caused
secretion of a saliva containing 0"52 per cent, of organic substance,
whilst, after a strong stimulation, a second weak one caused a secre-
tion having a percentage of 1'07 of organic substance.

- This, however, only holds when successive small quantities of
saliva are collected; with larger quantities, as 10 c.c. to 12 c.c,
no such after action is observed (Werther).

Stimulation of the Sympathetic Nekve supplying a
Salivary Gland.

Ludwig* (in 1856) discovered the secretory power of the sym-
pathetic; he obtained a secretion from the submaxillary gland of
the dog, by stimulating both the cervical sympathetic and the nerve
filaments on the gland artery.

1 "Werther, Arcli. f. d. ges. Physiol., Bonn, 1886, Bd. xx.xviii. S. 293 ; Laugley and
Fletcher, Phil. Trans., London, 1889, vol. clxxx. p. 109.

^ Heidenhain, Arch. f. d. ges. Physiol., Bonn, 187S, Bd. xvii. S. 40.

2 Heidenhain, op. cit., 1878.

^ Quoted by Czermak, Sitzungsh. d. k. ATcad. d. TFisscnsch., Wien, 1857, Bd. xxv. S. 3 ;
Czermak also obtained secretion on stimulating the cervical sympathetic.



STIMULA TION OF THE S YMPA THE TIC NER VE. 495

EckharcP noticed that the saHva secreted by the submaxillary
gland, on stimulation of the sympathetic, was more viscid and con-
tained a higher percentage of solids than that obtained by stimulat-
ing the chordo-lingual.

Neither from the submaxillary, the sublingual, nor the parotid
gland of any animal does the sympathetic produce a secretion which
approaches in amount that which is produced by the cranial nerve.
Unless the gland has been secreting under the influence of the cranial
nerve, before stimulation of the sympathetic (cf. p. 496), this stimula-
tion causes secretion of a few drops only, and it may be much less.
Thus, in the dog, stimulation of the sympathetic for a minute will
ordinarily produce two or three drops from the submaxillary gland, and
perhaps half a drop from the Sublingual.

In most of the earlier experiments upon the parotid gland of the
dog, either no secretion was obtained by repeated stimulation of the
sympathetic, or a total amount not exceeding a few drops. This is,
however, only a more marked instance of the slow secretion which the
sympathetic, after the first few stimuli, causes in the submaxillary and
sublingual glands of the same animal. If the parotid gland, after
sympathetic stimulation, during which no secretion or a trace only has
been obtained, be hardened, and sections be cut, the lumina, ductules,
and duct will be found distended with secretion.

The maximum total amount of saliva is obtained by stimulating the
sympathetic for short periods, with short intervals of rest. Stimulated
in this way — say, during every other half -minute — the sympathetic will
give from the submaxillary gland of the dog 3'oth to (^gtb of the
quantity of saliva that would be obtained by similar stimulation of the
chorda tympani.

With protracted stimulation the secretion may continue slowly for several
minutes, but sooner or later it stops. Roughly speaking, and Avithin rather
narrow limits, the amount of saliva obtained is inversely proportional to the
duration of the previous stimulus and directly proportional to the length of
the preceding period of rest. After repeated stimulation of the sympathetic,
there may be no visible secretion for half a minute to a minute after the
beginning of the stimulation, and occasionally the slight secretion which
occurs only begins after the stimulation has ceased.

Heidenhain, stimulating for a quarter of an hour during each halfdiour,
obtained a secretion from each stimulation for eleven successive hours, i.e. as
long as the experiment lasted.

In different glands, and in the same gland in different animals, the
freedom of secretion of sympathetic saliva compared with that produced
by the cranial nerve, and the percentage of organic substance in the
saliva, varies considerably. I have already mentioned that the
sympathetic causes some secretion from the submaxillary gland, and
often none from the parotid. Eelatively, rather more sympathetic
secretion is obtained from the glands of the cat and rabbit than from
those of the dog. The sympathetic saliva from the submaxillary gland
of the dog contains 1 to 3 per cent, of organic substance, that from the

1 Adrian and Eckhard, Beitr. z. Anat. u. Physiol. {Eckliard), Giessen, 1860, Bd. ii. S. 83.
Bernard, Journ. de I'anat. ei ^jJiysiol., etc., Paris, 1858, tome ii. (1) p. 657, stated that
sympathetic saliva was much more viscid than chorda saliva. The sympathetic secretion
in the sheep and rabbit was noticed by v. Wittich, Virchow's Archiv, 1866, Bd. xxxvii. S. 93.



496



THE SALIVAR Y GLANDS.



parotid of a rabbit 3 to 6 per cent. In the cat the percentage of
organic snbstance in sympathetic saliva from the submaxillary gland is
small (about O'O per cent.), and less than that in the chorda saliva.

The percentage of salts in sympathetic saliva does not exceed the
percentage of the salts in saliva produced by stimulating the cranial
nerve.

The analyses of the parotid saHva in the rabbit have been made by
Heidenhain.^ I extract the following from one experiment : —

Parotid Gland — Rathit.





Time of collect-
ing Saliva.


Amount of
Saliva.


Percentage
of Organic
Substance.


Percentage of

Salts.


Saliva from stimulating hoth
sympathetics .

Pilocarpine saliva from one
gland ....


38 min.
18 ,,


2-6 c.c.
4-2 „


4-93
0-65


0-54
0-81



The sympathetic saliva in the cat^ is, as I have said, usually less viscid
than chorda saliva. But it is possible that a strong or prolonged stimtdation
of the sympathetic might give rise to a saliva with a higher percentage of
solids than the chorda saliva. I append an analysis of sympathetic and chorda
saliva in the cat, obtained by moderately strong interrupted currents.





Percentage
of Organic
Substance.


Percentage
of Salts.


Percentage
of Solids.


Chorda saliva .
Sympathetic saliva .


0-87
0-43


0-34
0-28


1-21
0-70



The sympathetic secretion in the cat is very much like the " augmented "
secretion of the gland of the dog (cf. infra), in that it starts quickly,
quickly becomes slow, and is Avatery. It differs in the rapidity of recovery
from the effect of immediately preceding sympathetic stimulation. The
maximum amount of secretion is obtained by stimulating fifteen seconds out
of every thirty, or even for shorter periods.

In certain circumstances the sympathetic may produce a brief rapid
secretion from any or all of the salivary glands. That is the case when
it is stimulated shortly after stimulation of the cranial nerve. There is
a rush of saliva, quickly following the sympathetic stimulation, reaching
its maximum in a few seconds, and, after about seven to ten seconds,
rapidly declining. A very brief stimulation of tlie cranial nerve is
sufficient to increase in this way the amount of saliva obtamed from
the sympathetic. And thus, if the cranial nerve and the sympathetic
nerve be stimulated alternately, a not inconsiderable quantity of



^Arch.f. d.ges. Physiol., Bonn, 1878, Bd. xvii. S. 38.
^ Langley, Journ. Physiol., Cambridge and London, 1878, vol. i. p.
p. 92.



1885, vol. vi.



STIMULA TION OF THE S YMF A THE TIC NER VE. 497

sympathetic saliva may be obtained. It is convenient to have some
name for this unusually rapid sympathetic secretion, and I have called
it the augmented secretion}

In the dog, the saliva of the augmented secretion is, in its physical
characters and apparently in its percentage composition, intermediate
between sympathetic saliva and that obtained by stimulating the
cranial nerve.

The augmented sympathetic saliva from the submaxillary gland of
the dog is three to ten times as abundant as ordinary sympathetic
saliva. In fifteen seconds about ^ c.c. is usually secreted, but there
may be as much at ^ c.c. The amount of the augmented secretion from
the parotid is one-third to one-half that of the submaxillary gland.

The augmenting effect of stimulating the cranial nerve disappears
in time, although the sympathetic is not stimulated in the interval.
In the submaxillary gland of the dog the greater part of the effect dis-
appears in ten to fifteen minutes. In the parotid, it has usually com-
pletely disappeared in ten minutes. The rate of disappearance does not
seem to be affected by the injection of atropine.

Mere vascular dilation does not cause an augmented secretion, for
if atropine be given in sufficient quantity, to paralyse completely the
cranial secretory nerves, stimulation of the cranial nerve, which still
gives largely increased blood flow, does not increase to any considerable
extent the sympathetic saliva obtained subsequently.

When the sympathetic nerve is stimulated two or three times in
succession for rather short periods, say of thirty seconds, the augmenting
effect of a preceding cranial nerve stimulation does not necessarily cease
with the first stimulation, but is visible, though to a much less degree, in
the second, and it may be in later stimulations. In the case of the dog's
parotid the third stimulation usually gives no secretion at all.

The following extracts from the notes of experiments will illustrate the
statements made above with regard to the augmented secretion : —

Submaxillary Gland — Dog — Stimulation of the Symjpatlietic after moderate
Stimulation of the Chorda Tympani.



Saliva secreted in mm. during


















successive 30 sees., 35| mm.


















= -25 c.c


li


ij


1


1


531


20


1


20


Nerve stimulated .


sy.








Ch.






Sy-



In the second sympathetic stimulation the flow of saliva was 16 mm.
during the first fifteen seconds, and 4 mm. during the second fifteen seconds.

Submaxillary Gland — Dog — Stimulation of the Sympathetic after brief
Stimulation of the Chorda Tympani.

1 1^ 1
Sy.

Longer stimulation of the chorda tympani has little efi'ect upon the
maximum rate of flow of the augmented secretion, hut it leads apparently to a
less rapid fall after the maximum is attained.

^ Journ. Physiol., Cambridge and London, 1889, vol. x. p. 291.
VOL. I. — 32



Saliva ilow every








30 sees, in mm.


5 1





15


Nerve stimulated


Ch.
(for 2 to 3 sees.)




Sy.



498



THE SALIVARY GLANDS.



Parotid Gland — Dog-



Stimulation of the Sympathetic after Stimulation
of Jacohson^s Nerve.



Saliva flow every

30 sees, in mm.

Nerve stimulated



35
J.



31
J.



„„ (interval 11( ^ r,
' o "i minutes i' ^ ^
J. Sy. Sy. J



32



10

Sy.



14 1 3

Sy. Sy. Sy.

A brief rapid increase in the flow of saliva is obtained by stimulating.
the sympathetic during the action of pilocarpine and other alkaloids
which cause a continuous free flow of saliva. After the first rapid rise
the secretion becomes slower, and in the parotid gland of the dog stops
altogether ; in the submaxillary gland the secretion slowly continues.



Parotid Gland-
Rise of saliva 6



Dog — Pilocarpine Injected.
6 35 7 3



stira. synip.



Effect of Peotracted Stimulation on the Amount and
Percentage Composition of Saliva.

During protracted stimulation, as was shown by Becker and Ludwig,^
the percentage of solids in the saliva diminishes. They found a marked
diminution in the percentage of organic substance ; and generally, but
not always, some diminution in the percentage of salts. The most striking
experiment given by them is the following. The chorda tympani was
stimulated, and successive portions of the saliva were analysed : —





Amount
of Saliva
Collected.


Percentage of

Organic

Substance.


Percentage

of

Salts.


Percentage

of

Solids.


1st portion ....
2nd ,, ....
3rd ,, ....
4th ,


10-6
13-2
14-4
13-9


1-19

1-26
0-62
0-27


0-79
0-63
0-54
0-48


1-98
1-89
1-16
0-75



The decrease in the percentage of salts is probably connected, as
Heidenhain has pointed out, with the slower rate of secretion of saliva
in the later portions collected.

Heidenhain ^ showed that the percentage of solids sinks during pro-
tracted secretion, not only in chorda saliva,^ but also in sympathetic
submaxillary saliva. In the following experiment the sympathetic was
stimulated at short intervals during five and a half hours ; the first and
the last portions of saliva collected were analysed : —





Time of
Collection.


Amount
Collected.


Percentage
of Solids.


First portion .
Last ,,


80 minutes
88 „


0-68 grm.
0-89 ,,


3-73
1-49



1 Zlschr.f. rat. Med., 1851, K F., Bd. i. S. 278.

^ Stud. d. physiol. Inst. r:u Bo-eslau, Leipzig, 1868, S. 65.

2 We have to refer so frequently to the saliva obtained from the submaxillary gland —
(1) by stimulating the chorda tympani, (2) by stimulating the sympathetic, (3) by
injecting pilocarpine — that we are driven to adopt the terms, chorda saliva, sympathetic
saliva, and pilocarpine saliva, for the saliva obtained respectively in these circumstances.



RELATION OF RATE TO PERCENTAGE COMPOSITION. 499

He ^ showed, further, that m parotid sahva, obtained by stimulating
Jacobson's nerve, there is similarly a decrease in the ];)ercentage of solids
as the secretion goes on, and, no doubt, it is a general rule for all
salivary glands.



Eelation of the Eate of Secretion to the Percentage
Composition of Saliva.

Heidenhain ^ investigated the relations existing between the rate of
secretion and the percentage composition of saliva. He showed that an
increase in the rate of secretion was accompanied by an increase in the
percentage of salts, and this whether the gland had secreted for a long
time or for a short time.

An example of this is given in the following experiment, in which the
chorda tympani was stimulated with currents of varying strength, and a few
c.c. of sahva collected in each case. The samples of saliva are arranged in the
table in the order of their rate of secretion : —



Order of sample


5


1


7


3


8


4


2


Mean rate of secretion
















per min. in c.c..


•15


•18


•19


•22


1-6


2-0


2-2


Percentacje of salts .


•34


•29


•25


■32


•37


•58


•44



•57



3-2

•58



It will be noticed that the percentage of salts does not quite go hand
in hand with the rate of secretion. But it is almost impossible to keep
the rate of secretion constant during the time of collecting a sample of
saliva, and to this the divergences may, in the main, be attributed.

A closer relation between the rate of flow and the percentage of saliva was
observed by Werther,'^ and by Langley and Fletcher.'^ Heidenhain found the
percentage of salts to have an upper limit, with increased rate of secretion.
This he gave as •S to "6 per cent., though in one case •GG per cent, was found.
Becher and Ludwig had earlier found in one case -78 per cent. Werther, and
Langley and Fletcher found the maximum percentage to be '11. From the
observations of the latter, it appears that the faster the rate of secretion, the
less increase there is in the percentage of salts for a given increase in rate of
secretion. This is indicated in the following table : —







Increase in Percentage


Rate of Secretion per
Minute in c.c.


Percentage of Salts.


of Salts, correspond-
ing to an Increase of
O-l c.c. per Minute
in the Rate of Secretion.


•400


•472"!


•04


•500


•5I2J




•760


•599


•033


•900


•616


•012


1^333


•628


■003



^ Heidenhain, Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xvii. S. 23. During eleven
hours' stimulation the percentage of solids sank from 0'88 per cent, to 0^49 per cent.

^ Ibid., Bd. xvii. p. 1. Earlier observations on the same lines Avere given by him in
1868 in his " Studieii."

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

* Phil. Trans., London, 1889, p. 109.



500



THE SALIVAR Y GLANDS.



The experiments on the parotid gland given by Heidenhain show a
general but not a very close relation between the rate of secretion and the
percentage of salts in the saliva.

Sodium chloride forms the larger part of the salts in saliva. The
percentage both of this and of sodium carbonate varies directly with the
rate of secretion.^ The salts insoluble in water, the chief of which is
calcimn carbonate, do not seem to follow this rule, or at any rate only
partially, for, whilst there is sometimes an increase in the percentage
of insoluble salts, with increased rate of secretion, this is by no means
always the case;^ thej appear to decrease in amount during the
progress of the secretion, as if in part they arose from a store in the
gland itself.

The following experiment from Werther will illustrate the variations in
the percentage of different salts. The saliva was obtained from a dog by
stimulating the chorda tympani : —





Amount

of Saliva

obtained

in c.c.


Rate of

Secretion

per Minute

in c.c.


Percentage

of

Organic.

Substances.


Percentage

of

Salts.


Percentage

of

Insoluble

Salts.


Percentage
of

NaCl.


Percentage
of

Na„C03.


1


17-6


0-176


0-30


0-35


0-019


0-29


0-042


2


14-2


0-890


1-12


0-43


0-060


0-30


0-067


3


16-2


0-216


0-12


0-21


0-015


0-13


0-029


4


16-2


1-082


0-64


0-42


0-030


0-27


0-046



The relation thus determined between the percentage of salts and
the rate of secretion, holds for chorda saliva and for pilocarpine saliva -
secreted under normal conditions. But it is not a universal rule. Thus,
sympathetic saliva has a much higher percentage of salts than corre-,
sponds to its rate of secretion, if chorda saliva be taken as a standard of
comparison. And the rule does not hold for chorda or pilocarpine saliva,
when the blood flow through the gland is much diminished, or when
the character of the blood is much altered. On this I shall say more
presently.

Heidenhain also showed that in a fresh gland an increase in the rate
of secretion is accompanied by an increase in the percentage of organic
substance in the saliva. In the experiment given below, for example,
an increase in the rate of flow of the submaxillary saliva of the dog,
from 0*14 c.c. to 0"87 c.c. in one minute, was accompanied by an increase
from 0-52 to 1'54 in the percentage of organic substance. But when
a certain amount of the stored-up substance of the gland cells has been
secreted, an increase in rate of secretion no longer leads to an increase
in the percentage of organic substance in the saliva secreted in a
given time.

The closeness of the relation between percentage of organic sub-
stance and rate of secretion from a fresh gland seems to me to have
been much exaggerated. No doubt there is a relation of the kind, but,
in actual experiments, it is frequently overridden by other factors.

^ Werther, oj>. cit. - Langley and Fletcher, oj). cit., snjjra.



SOME GENERAL CHARACTERS OF SALIVA.



501



Interval
between each
Period of Col-
lection and the
one before it.


Amount of
Saliva in c.c.


Rate of Secre-
tion in c.c. per
Minute.


Percentage

of

Organic

Substance.


Percentage

of

Salts.


Total

Percentage

of

Solids.




3-5


0-14


0-52





22





74


2 minutes


3-5


0-87


1-54





06


2


10


^\ „


3-0


0-66


1-63





45


2


08


20


2-8


0-11


1-07





36


1


44


2


3-0


TOO


0-91





49


1


41


2


3-0


0-50


0-76





39


1


16


13 „


2-5


0-13


0-48





30





78


3


3-1


0-77


0-51





38





90


1


2-8


0-31


0-42





36





79



Some Genekal Chaeacteks of Saliva, and its Microscopic

Constituents.

The viscidity of saliva, secreted by mucous glands, is generally in
proportion to the percentage of mucin which it contains. This, of
course, would not be the case, if the amount of alkaline salt in the
saliva increased in much larger proportion than the amount of mucin,
for, with a given quantity of mucin, the viscidity of the fluid varies with
the amount of the solvent.

Saliva, from albuminous or from mixed glands, may be either watery
or thick, irrespective, within certain limits, of the percentage of organic
substance present. Sublingual saliva and parotid saliva of the dog,
when they have a high percentage of organic substance, have a tendency
to turn into a jelly-like mass, and this may further separate into a clot
and clear fluid.

In very watery saliva, freshly secreted, which has not been allowed
to stand in the ducts, and which is examined without delay, nothing is
to be seen under the microscope.

When saliva is allowed to stand a short time in the ducts, car-
bonic acid is given off from it, and, in consequence, calcium carbonate
is precipitated ; the precipitate renders the saliva cloudy, and under



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