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AGENTS ACTING ON ORGANS OF SPECIAL SENSE.
muscle resulting in temporary loss of accommodation, the eye remaining focussed for distant objects, and the intra-ocular tension being increased.
The dilating action of Atropine and its congeners is due to stimulation of the endorgans of the sympathetic nerve, increasing the power of the radiating muscular fibres of the iris, and also to paralysis of the end-organs of the motor oculi (3d cranial) nerve, lessening the power of the circular fibres or sphincter iridis. When administered internally the drug is carried by the circulation to the eye, acting thereon locally as if instilled directly upon the conjunctiva. The principal mydriatics are those named in the following list, viz.:
Belladonnine (internally only).
Gelsemine (locally only).
Anæsthetics (at last).
Atropine, Duboisine and Homatropine are the mydriatics used by ophthalmologists.
Myotics (meuo, I close),- are agents which produce contraction of the pupil. The alkaloid of Physostigma, Eserine, is the chief local myotic, and the only one used in ophthalmic practice. It acts by stimulating the circular muscular fibres of the iris, at the same time contracting the ciliary muscle so that the eye is accommodated for near objects only, and diminishing intra-ocular tension; in all of which it exactly antagonizes the action of Atropine.
Muscarine, Pilocarpine and Nicotine are also local myotics, acting upon the end. organs of the oculo-motor nerve. Anæsthetics in the early stage of their action cause contraction of the pupil by lessening reflex action; later, when they begin to paralyze respiration the accumulation of venous blood irritates the centres and produces dilatation, which is a sign of failing respiratory power during anesthesia. The myotic action of Opium is of central origin, probably the paralysis of the local reflex excitability. The chief myotics are as follows:
Anæsthetics (at first).
The Sensibility of the Eye is increased by Strychnine, the field of vision becoming extended, and the vision rendered more acute. If the drug be administered hypodermically the improvement will be more marked in the eye corresponding to the side of the body where the injection was made.
The sensibility for color is affected by drugs, Strychnine increasing the field for blue, Eserine diminishing it for red and green, and Santonin causing objects to appear at first of a violet and afterwards of a greenish-yellow color.
Visions are produced by several drugs, their action being probably on the cerebral sight-centres (angular gyrus and occipital lobes) rather than on the eye. Alcoholic delirium is a familiar instance, while Cannabis Indica often causes pleasant visions, and Sodium Salicylate in some persons produces very disagreeable ones. Digitalis may produce subjective sensations of the continued presence of light. Bromides in e
may produce visions of such intensity that their subject remembers them distinctly for years afterwards.
Amblyopia, or impairment of vision from nerve-changes, is produced temporarily by Quinine, and may be permanently induced by Tobacco, Alcohol, Lead and Urea.
The Ear is affected by several drugs. Strychnine and Morphine increase the excitability of either the auditory nerve or the centre for hearing (superior temporo-sphenoidal convolution), making that faculty much more acute. Quinine, Antipyrine and Salicylates produce hyperamia of the auditory apparatus, causing subjective noises, as humming, buzzing or ringing, which are very unpleasant. Hydrobromic Acid and the Bromides, also Ergot, will diminish the congestion and to a great extent will neutralize or prevent these noises.
Quinine in large doses is believed by some to have produced permanent injury of the sight and the hearing, but authentic cases of such action are extremely rare, if indeed they can be found at all. Temporary deafness is often caused by Quinine, but it usually disappears soon after the administration of the drug is stopped.
The Sense of Smell is also increased by Strychnine, and decreased by all cerebral depressants and by those agents which produce changes in the nasal mucous membrane, e. g., Potassium Iodide.
The cerebral centre for this faculty is situated at the tip of the temporo-sphenoidal lobe, and the terminal branches of the olfactory nerve are distributed upon the mucous lining of the upper portion of the nasal fossæ. Strychnine probably stimulates the former, and all drugs acting upon the latter region would have more or less effect upon the power of distinguishing smells.
The Taste is not much affected by drugs except as each makes its peculiar impression on the nerves of taste, and may overcome that of another agent. Smell has much to do with taste in many instances, the expedient of holding the nose while swallowing Castor Oil being familiar to every one.
The "after taste" of drugs is often different to their original taste; thus Bitters are said to leave a sweet "after-taste, and the same is claimed for Quinine if given in acid solution so as to be entirely dissolved, and if washed out of the mouth with water immediately after swallowing. Substances which are excreted from the system in the saliva (as Iodides) leave a very persistent after-taste.
AGENTS ACTING ON RESPIRATION.
The Respiratory Centre is situated in the medulla oblongata, close to the termination of the calamus scriptorius. It probably consists of thoracic and diaphragmatic Inspiratory centres, the act of expiration being considered normally a passive one, due to the natural contraction of the walls of the air-vesicles, and the return of the diaphragm and thoracic
AGENTS ACTING ON RESPIRATION.
walls to the position from which they were moved by the inspiratory effort. An Expiratory Centre must also exist for the initiation of forced expiration, as in the production of voice, cough, sneezing, etc. The chief Inspiratory Nerves are the pulmonary branches of the vagus. The Expiratory Nerves are the nasal branches of the fifth, the superior and inferior laryngeal, and the cutaneous nerves of the chest and abdomen.
Respiratory Stimulants exalt the function of the respiratory centre, quickening and deepening the breathing. Such agents, besides Opium in small doses, are
Strychnine also stimulates the vagus tract. Electricity applied to the nerve-trunks or to the inspiratory muscles, is a direct respiratory stimulant. Veratrine, Eserine, and Muscarine stimulate the vagus terminations, quickening the respiration, but afterwards slow it by depressing the respiratory centre. Aconite stimulates the end organs of the vagus when given in small doses.
Respiratory Depressants lower the activity of the respiratory centre, rendering the respirations slow and shallow. The chief agents of
The ten last named first excite the centre for a brief period and then depress it.
Pulmonary Sedatives diminish cough and dyspnoea by lessening the irritability of the respiratory centre or the nerves of respiration. Some act by directly depressing the respiratory centre, as those enumerated under the preceding head; others by removing some irritant from the passage, or by lessening local congestion, as the expectorant group; and others by lowering the excitability of the vagus end-organs in the lungs, and other afferent filaments throughout the respiratory tract.
Opium has the most powerful influence as a sedative to the respiratory centre, and mucilaginous or saccharine substances soothe the local irritation, hence the latter are so frequently used as vehicles for the former in cough mixtures. Hydrocyanic Acid has a similar sedative action, hence the use in coughs of Prunus Virginiana and other substances containing it. Belladonna stimulates the respiratory centre, but at the same time lessens the excitability of the vagus terminations in the lungs, and completely arrests secretion from the bronchi. Stramonium acts similarly. The principal pulmonary sedatives may be enumerated as follows:
Errhines and Sternutatories (en, in, rhin, the nose; sternuto, I sneeze),—are agents which produce increased nasal secretion and sneezing, when locally applied to the mucous membrane of the nose. The first term is usually applied to substances which cause increase of the mucus without sneezing, the latter to those which invariably produce sneezing. The drugs should be in powder for application. The stimulus produced by these agents is transmitted by the nasal branches of the fifth nerve to the respiratory centre, exciting the sudden and forcible expiratory effort called sneezing; also to the vaso-motor centre, contracting the smaller vessels throughout the body and producing a general rise in the blood-pressure. The principal agents of this class are
The last two named may be used as simple Errhines, as the vapor of dilute Ammoniawater or the smoke of burning Cubebs do not excite sneezing generally.
Expectorants (ex, out of, pectus, the breast),-are remedies which modify the secretion of the broncho-pulmonary mucous membrane, and promote its expulsion. They may be divided into
Nauseating Expectorants,—in large doses act mechanically by expelling the mucus in the act of vomiting, in small doses by increasing osmosis from the inflamed mucous membrane. The members of this subdivision generally increase secretion and tend to lower the blood-pressure. The chief of them are the following named :—
Antimony, Tartar Emetic.
Stimulant Expectorants,-are largely eliminated by the bronchial mucous membrane which they stimulate, altering the secretion and facilitating expectoration. These remedies generally diminish secretion and increase blood-pressure. They are
Besides the above many other remedies may act as expectorants, some by relieving bronchial spasm, as Opium, Stramonium, and Tobacco,-others by soothing the irritable respiratory centre, as Opium and Chloral,-and the ciliary excitants by reflex action through their impression on the nerves of the mouth.
AGENTS ACTING ON THE CIRCULATION.
Ciliary Excitants,-promote the expectoration of bronchial mucus by their reflex excitation of the tracheal and bronchial cilia, when dissolved in the mouth. Gum Acacia, Ammonium Chloride, Potassium Chlorate, and native Chloride of Sodium have this action.
AGENTS ACTING ON THE CIRCULATION.
Cardiac Stimulants rapidly increase the force and frequency of the pulse in depressed conditions of the cardiac apparatus. One of the most useful agents of this class is Alcohol in some form, its action being largely due to a reflex influence excited through the nerves of the mouth and stomach. It should therefore be given in but slightly diluted form, and in small quantities frequently. Ether is next in value and still more rapid in action, and Heat is one of the most powerful and available of the class. Ammonia has an energetic action as a stimulant to the vaso-motor centre, as well as a reflex one upon the heart similar to that of Alcohol. The list of cardiac stimulants includes the following, viz. :—
Cardiac Tonics, when given in moderate doses, stimulate the cardiac muscle, slowing and strengthening its contractions. In large doses they are apt to produce irregular action of the heart, and some of them have more or less of a tendency to cause sudden death by syncope if pushed to any great extent. The most important of these agents are
Digitalis acts partly by stimulation of the vagus end-organs in the heart, thus increasing cardiac inhibition, and partly by direct stimulation of the cardiac centre in the medulla, as well as by a direct influence on the heart muscle itself. Convallaria, Erythrophlæum, Squill, and Cimicifuga act similarly but less powerfully, and are correspondingly safer. Strophanthus is still better, as it does not affect the vessels, and therefore does not raise the blood pressure.
Cardiac Sedatives lessen the force and the frequency of the heart's action and are used to control palpitation of that organ, and to slow the pulse in febrile conditions in sthenic subjects, especially when local inflammation is the exciting cause. The chief cardiac sedatives are—