Substances which excite vomiting, independent of any effect arising from
the stimulus of quantity, or of that occasioned by any nauseous taste or
flavour.
Before we can determine the _modus operandi_ of emetics, it will be
necessary to take an accurate view of the phenomena and pathology of
vomiting. It is an important fact that any extraordinary stimulus
applied to the stomach, instead of increasing its motions, as it would
in other instances, actually inverts them: the wisdom of such a peculiar
provision is manifest; it is intended to prevent the protrusion of the
food into the duodenum before it has undergone those necessary changes
in the stomach, by which it is prepared for the more elaborate process
of chylification. The act of vomiting, however, is not effected, as Dr.
Haygarth formerly supposed, by the sole influence of the stomach; the
brain is an important accessary: Dr. Majendie goes so far as to
attribute the operation of vomiting, exclusively, to the agency of this
latter organ upon the abdominal muscles, and regards the stomach as a
mere passive instrument in the act;[150] this doctrine was supported in
an elaborate experimental memoir, presented by this indefatigable
physiologist to the Royal Institute of France in the year 1812.
Although we shall not be disposed to receive this theory in its full
extent, yet we cannot hesitate to admit that the influence of the
nervous system is indispensably necessary for producing vomiting; and we
accordingly find that this act will not take place, however forcibly the
stomach may be goaded by emetics, where the energy of the nervous system
is suspended, as in cases of profound intoxication, or in violent wounds
and contusions of the head; while if the brain be only partially
influenced, as by incipient intoxication, or by a less violent blow upon
the head, its irritability is increased instead of being paralysed, and
vomiting under such circumstances is excited by the slightest causes:
the fact of such opposite results being produced by the same impulse in
different degrees of intensity, is no less curious than instructive. Dr.
Richard Harrison, in his Gulstonian Lecture before the College of
Physicians, treated the subject of vomiting with much ingenuity, and I
am disposed to adopt the views which he offered. He observed, that
although the experiments of Majendie sufficiently testify the importance
of the pressure of the abdominal muscles upon the stomach in the act of
vomiting, and which can only be explained by the influence of the brain
and nervous system, yet that he has attributed too much to their agency;
“it appears to me,” continued he, “that vomiting may be explained in the
following manner:—_the irritation of the stomach makes a call upon the
brain for the aid of the diaphragm and the abdominal muscles, in order
to expel its contents; the diaphragm then becomes contracted and fixed,
the ribs drawn down, and the abdominal muscles drawn inwards, so that
the stomach is pressed on all sides by voluntary muscles, which,
together_ WITH ITS OWN CONTRACTION, _expel the contents_.” Now it must
be obvious that where the brain, from oppression or injury, is unable to
transmit its influence to these muscles,[151] and disregards the call of
the stomach, vomiting can only be excited with difficulty, or it will be
prevented altogether.
Under such circumstances venesection may in some cases prove a powerful
adjuvant, by unloading the vessels of the brain, and thus restoring to
the nervous system its necessary excitability; where its powers have
been paralysed by the operation of a narcotic, a copious draught of some
vegetable acid, or the affusion of cold water upon the surface of the
body may impart efficiency to an emetic; the operation of _Nightshade_
and some other narcotic poisons may be adduced in farther illustration
of this subject;—an excessive dose of the _Atropa Belladonna_ produces
symptoms of alarming stupor, and so difficult is it to evacuate the
stomach under such circumstances, that as much as fourteen grains of
_Tartarized Antimony_ have been administered without effect: now if in
such a case a copious draught of some vegetable acid be given, the
emetic will be more likely to succeed: here then we perceive, that the
brain, being paralysed by a narcotic poison, is unable to lend its aid
to the muscles requisite for the operation of vomiting, until its
energies are restored by the anti-narcotic powers of a vegetable acid.
The practical precaution which this view of the subject affords, is
extremely important,—_not to allow the apparently inactive state of the
stomach to induce us, inconsiderately, to augment the dose of an
emetic:_ for although the stomach, for the reasons just stated, may be
unable to void its contents by vomiting, it may nevertheless retain its
sensibility, and be therefore liable to inflammation: Dr. Harrison has
reported a case of this kind, where the practitioner, in attempting to
excite emesis in an epileptic patient, by a very large dose of _sulphate
of zinc_, produced an inflammation in the viscus that terminated
fatally.
Vomiting may also be produced by the _primary_ operation of certain
agents upon the brain, by which its energy is disturbed, as by
narcotics, or by the motions of swinging, whirling, and sailing: in such
cases, the series of actions necessary for the establishing of vomiting,
commences in the brain, and is propagated by nervous sympathy to the
stomach.
When an emetic is taken into the stomach, an interval of twenty minutes
or longer, usually passes without any apparent effect; an uneasy
sensation, which we term nausea, is then felt, and this continues to
increase until vomiting begins; here then we perceive are two distinct
stages, each of which is marked by its own proper symptoms; the relative
intensity and duration of which will be found to vary according to the
nature of the exciting causes; thus some Emetics, as _Sulphate of Zinc_,
act without occasioning much nausea, while others, as _Tobacco_ excite
it to a degree which is far greater than is proportioned to their emetic
power: this is a fact of great importance in directing us in the
selection of an Emetic, for we shall find that in some diseases it is a
great object to avoid that state of system which invariably accompanies
nausea, while in others it affords the best mode of answering an
important indication of cure.
Nausea would seem to depend upon the exertions of the stomach and
muscles, not being proportioned to the effects of the brain, in order to
produce vomiting. Where this balance however is maintained, as during
the operation of an ordinary emetic, the following are the symptoms
which characterise the two stages;—while the nausea only is present, the
countenance is pale and shrunken, the pulse feeble, quick, and
irregular, and there is a feeling of cold; but as soon as vomiting
commences, the face becomes flushed, the pulse quicker and stronger,
although it seldom returns to its natural standard, until some time
after the vomiting has ceased. A degree of languor, a disposition to
sleep, and a general moisture upon the skin, are the circumstances which
occur after the total cessation of the paroxysm.
The feeble state of the circulation, as indicated by the pulse, and the
general coldness and languor experienced during a paroxysm of nausea,
are to be ascribed to those sympathetic relations by which the brain,
stomach, and heart, are reciprocally influenced.
The advantages to be obtained from the administration of an emetic in
the cure of disease, may either depend upon its _primary_, or
_secondary_ operations, that is to say, upon the mere evacuation of the
stomach, or upon those changes which occur in distant parts from
sympathy; and the judicious practitioner, in the selection of an emetic,
will always be guided by the nature of the indication which he intends
to fulfil; if his object be to evacuate the stomach quickly and
completely, he will avoid those emetics that are distinguished by their
nauseating tendency, as in cases of disease which depend on a disordered
state of stomach, connected with undue distention, and the presence of
acrid and indigestible matter; if, on the other hand, his intention be
to influence some remote organ through the sympathetic powers of the
stomach, an emetic of an opposite tendency may be better calculated to
answer such indications: in some cases, he is to seek a beneficial
result from the mechanical action of the diaphragm and abdominal
muscles, by whose pressure the gall-bladder and hepatic ducts are
emptied of their contents, and hence jaundice, arising from the
obstruction of biliary calculi, has been suddenly removed by the
_concussion_ of an emetic: a similar pressure upon the thoracic viscera
may occasion expectoration, and relieve the bronchial vessels in cases
of asthma, catarrh, and croup.
Vomiting, when produced by the operation of a mild emetic, does not
appear to exhaust the excitability of the stomach, but on the contrary
to increase its tone; for we generally find the process of digestion is
carried on more vigorously afterwards; although it is probable that, by
frequent repetition, a different result would be obtained, and we should
find that its motion would become liable to inversion by slight stimuli:
we may therefore question the propriety of that practice which is so
strenuously recommended by Hippocrates,[152] and other ancient
physicians, to administer emetics frequently to those in health, in
order to prevent the incursions of disease.
The benefits arising from the secondary effects of an emetic are
numerous and extensive. It has been observed that during nausea the
force of the circulation is considerably abated, hence the use of these
remedies in hemorrhage; and, as the energy of absorption is generally in
an inverse ratio to that of the circulation,[153] we frequently obtain
from a nauseating dose of an emetic, considerable assistance in the
treatment of anasarca, and other dropsical swellings. Those medicines
that are liable to produce at once, full vomiting, without any previous
stage of nausea, are of course less calculated to fulfil such
indications. In the same manner we should select a _nauseating_ emetic,
when our object is to promote the passage of a gall stone through the
_ductus communis_, for the nausea so excited will relax the duct, while
the mechanical concussion tends to push the obstructing matter forward.
On the other hand, whenever our object is to evacuate the stomach, and
to prevent absorption, we must take care to cut short the nauseating
stage; a precaution which is highly important in the treatment of a case
of poisoning. The state of the stomach produced by vomiting is very
frequently extended, by sympathy, to the vessels of the skin; in
consequence of which, a diaphoresis not unusually follows the operation.
In the different varieties of febrile disease, this circumstance stamps
additional value upon the class of Emetics; while, at the same time,
that they eject any offensive matter which may be present in the
stomach, they thus control the accelerated circulation.
From the violent muscular exertions which take place in the act of
vomiting, the administration of an emetic may be very injurious in
certain states of the body. In consequence of the pressure applied to
the descending aorta, and the interrupted circulation through the lungs,
from impeded respiration, the blood returns with difficulty from the
head during a paroxysm of vomiting, and in plethoric states of the body,
or in cases of determination of blood to the cerebral or pulmonary
organs, the act of vomiting cannot be considered as free from danger.
The concussion of an emetic may also produce mischief in the advanced
stage of pregnancy, and in _hernia_ and _prolapsus uteri_; while in
extreme debility, there is the danger of a syncope being produced, from
which the patient may never recover, as I once witnessed in the last
stage of Phthisis, where an emetic was imprudently given, with the
intention of dislodging the pus with which the lungs were embarrassed.
By violent and protracted retching, a person will sometimes become
jaundiced; the stomach, diaphragm, and abdominal muscles, are, under
such repeated efforts, apt to be rendered, to an eminent degree,
irritable; so that at each effort of the former to discharge its
contents, the latter will frequently be thrown into strong spasmodic
contractions, and the liver together with the gall bladder will be
suddenly caught, and, as it were, squeezed in a powerful press; in
consequence of which the bile will regurgitate, and be carried into the
_Venæ cavæ_; for Haller has shewn with what facility a subtle injection,
when thrown into the hepatic duct, will escape by the hepatic veins; and
upon which Dr. Saunders observes, “I know this to be a fact, for I have
ascertained by experiment, that water injected in the same direction,
will return by the veins in a full stream, though very little force be
used.” When a jaundice is thus produced it will gradually disappear
without the aid of any medicine; the kidneys are the principal means by
which all unnecessary bodies are extracted from the circulating mass, a
portion of bile will therefore under such circumstances be eliminated in
every discharge of urine.
The different emetics employed in practice are derived from the
vegetable and mineral kingdoms, some of which appear to produce their
effects by an immediate impression upon the nerves of the stomach, while
others require to be absorbed into the circulation before they display
their energies. _Ipecacuanha_ would seem to act primarily on the
stomach, but _Tartarized Antimony_ has been found, by experiment, to
occasion vomiting, when injected into the veins of an animal; while the
other mineral emetics, _viz._ the preparations of _Copper_ and _Zinc_,
undoubtedly operate on the stomach, and without inducing much nausea.