Читать книгу Pharmacologia - John Ayrton Paris - Страница 32

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.