Agents Acting on Respiration.

Respiratory Stimulants,—exalt the function of the respiratory centre in the medulla, quickening and deepening the breathing. The most important of these agents are—Strychnine, Atropine, Thebaine, Digitalis, Ammonia, Heat, Electricity, Tobacco (briefly), Alcohol (briefly), Ether (briefly), and Opium (in small doses).

Respiratory Depressants,—lower the actions of the respiratory centre, rendering the respirations slow and shallow. The chief members of this group are—Opium (in full doses), Gelsemium, Aconite, Veratrine, Conium, Chloral, Alcohol, Ether, Chloroform, Caffeine, Cold, etc. Many of these at first excite the centre, but soon depress it.

Pulmonary Sedatives,—relieve cough and dyspnoea, by lessening the irritability either of the respiratory centre or of the nerves of respiration. Some act by direct depression of the respiratory centre, (as the Depressants above enumerated);—others by lessening local congestion, as the Expectorants, (see below)—and others by lowering the excitability of the vagus end organs in the lungs and other afferent filaments throughout the respiratory tract. The most powerful of these directly sedative agents is Opium, and next are Hydrocyanic Acid and Potassium Cyanide. Others are—Belladonna and its congeners, which stimulate the centre but depress the vagus end-organs, and arrest secretion in the bronchi ;—Cannabis Indica, Quebracho, Codeine, Amyl Nitrite, Turpentine, Iodide of Ethyl, Conium, Tobacco, etc.

Expectorants, (ex, out of, pectus, the breast),—are agents which modify the broncho-pulmonary mucous secretion, and promote its expulsion. They, consequently, act as pulmonary sedatives, indirectly; and are subdivided into—

Nauseating Expectorants, in small doses increase osmosis from the inflamed mucous membrane, in large doses cause vomiting and the mechanical expulsion of the mucus. They also increase secretion generally, and lower the blood pressure. Such are Antimonial salts, (Tartar Emetic, etc.), Ipecacuanha, Lobelia, Jaborandi, Apomorphine, Alkalies, etc.

Stimulant Expectorants,—are eliminated from the system largely by the bronchial mucous membrane, which they at the same time stimulate, thus altering its secretions, and facilitating expectoration. They diminish secretion generally, and increase the blood pressure, and include the Ammonium salts, Balsams of Peru and Tolu, Benzoin, Ammoniac, Squill, Senega, Nux Vomica, Terebenthinates, Sulphur, Saccharine substances and Acids.

Ciliary Excitants,—promote the expulsion of bronchial mucus by their reflex excitations of the tracheal and bronchial cilia when dissolved in the mouth. This group includes such agents as the Chlorides of Ammonium and Sodium, Potassium Chlorate, and Gum Acacia.

Errhines and Sternutatories,—are agents, which, when locally applied to the nasal mucous membrane, produce sneezing and increase of the nasal secretion. The first term. (en , in, rin , the nose), is usually applied to substances which simply increase the mucous discharge,—the second, (sternuto, I sneeze), to those which invariably produce the violent expiratory effort called sneezing. Both should be in powder form for application. Another result of their use is the stimulation of the vaso-motor centre at the same time that they excite the respiratory centre,—thus producing a contraction of the smaller vessels throughout the body, and consequently a general rise in the blood pressure. This class includes—Ammonia-vapor (dilute), Cubeb smoke, etc., which are simple errhines,—and the vapor of Ammonia-water, also Tobacco, Ipecacuanha, Sanguinaria, Ginger, Veratrum Album, etc., in powder, as snuff.

A Compend of Materia Medica, Therapeutics, and Prescription Writing, 1902, by Sam'l O. L. Potter, M.D., M.R.C.P.L.