Agents Acting on the Digestive System.

Dentifrices, (dens, a tooth, frico, I rub),—are medicated pastes or powders employed with a stiff brush to cleanse the teeth and gums. Their base is usually Chalk, for its mechanical action and its alkaline quality; besides which, there should be some antiseptic, as Quinine, Borax, etc., and an aromatic stimulant , like Myrrh.

The Teeth are injuriously affected by several drugs, especially the Mineral Acids, and the Persalts of Iron. These should always be administered through a glass tube, and the mouth should be rinsed out afterwards with a weak alkaline solution.

Dental Anodynes,—employed locally in toothache due to caries exposing a nerve filament, are Aconite, Opium and Cocaine salts,—also Carbolic Acid, Creosote, Chloral , and Potassium Chlorate. A solution, containing the three first named, applied on a pledget of cotton, will promptly relieve whenever the nerve is accessible. Chloral should never be employed for this purpose, as in solution sufficiently strong to be of any service it is very apt to cause sloughing of the gum, especially if injected thereinto by a hypodermic syringe, as is frequently done by ignorant dentists, who advertise the "extraction of teeth without pain."

Sialogogues, (σιαλον, saliva, αγω, I carry off) ,—are drugs which promote the secretion and flow of saliva and buccal mucus. They may be subdivided into two groups, viz.:—

Topical Sialogogues,—which act by reflex stimulation,—including the Acids and Alkalies, Ether, Chloroform, Mustard, Ginger, Pyrethrum, Mezereon, Tobacco, Cubeb, Capsicum, Rhubarb, etc.

General Sialogogues,—which influence the glands or their secretory nerves, viz.—Pilocarpus (Jaborandi), Muscarine, Physostigma, Ipecac, Iodides, Mercurials and Antimonials, etc.

Antisialics,—are agents which diminish the secretions of the salivary and buccal glands. The typical member of this group is Atropine, which acts by paralyzing the terminal filaments of the secretory nerve. Physostigmine antagonizes this paralysis, but in large doses acts also as an antisialic, by lessening the blood supply to the glands. Opium diminishes this secretion among many others, and also lessens the excitability of the reflex centre, by which the secretion is largely stimulated. Others acting locally are—Lime, Soda, Lithia, Magnesia, Borax, Potassium Chlorate, and insipid or nauseous articles of food or medicine.

Refrigerants,—are remedies which impart a sensation of coldness, (refrigero, I cool), and thereby allay thirst and restlessness. Among them are the Vegetable and Mineral Acids, (greatly diluted, especially the latter), Ice, Cold Water, Effervescing drinks, Fruit juices, and many diaphoretics.

Gastric Tonics or Stomachics—increase the appetite and promote gastric digestion. Some act by stimulating the production of the gastric juice, among which are Alkalies before meals;—others by stimulating the local circulation, as the Aromatic Oils, Aromatic Bitters, Alcohol, Ether, etc.;—and several by exciting the activity of the nervo-muscular apparatus of the stomach, as Nux Vomica, Arsenic, Hydrastis, dilute Acids, etc. The various Digestive Ferments, such as Pepsin, Ingluvin, and dilute HCl Acid, are adjuvants to digestion, and are used to supplement the gastric juice when deficient in quantity or quality.

Acids,—considered physiologically and therapeutically, are medicines which in concentrated form act usually as caustics, to destroy the tissues; but when administered internally in medicinal doses they check the production of glands having acid secretions if coming in contact with the mouths of their ducts,— and increase the production of those having alkaline secretions. Thus, a dilute acid given before meals will check the production of the acid gastric juice, but will stimulate that of the alkaline pancreatic juice. They should always be largely diluted for internal administration. The principal Acids are Acetic, Citric and Benzoic, from the vegetable kingdom, and Nitric, Phosphoric, Sulphuric and Hydrochloric from the mineral kingdom.

Alkalies, or Ant-acids,—from the same stand point, are agents which neutralize acids, also act as escharotics on the tissues, and check alkaline and stimulate acid secretions, when in contact with the mouths of the ducts of the glands producing them. Thus, a dilute alkali given before meals will stimulate the production of the acid gastric juice, and if applied to the mouth of the pancreatic duct will check the secretion of the alkaline pancreatic juice. Alkalies may be subdivided into two groups, named, from their physiological actions,—Direct Antacids, those which lessen the acidity in the stomach, and Indirect or Remote Antacids, which have no power over the acidity in the stomach, but are oxidized in the blood, and excreted as Carbonates in the urine, and lessen its acidity. The following List of Alkalies comprises the chief members of both groups, and also some which have the actions of both. They should all be largely diluted before administration.

Emetics, (εμεω, I vomit),—are agents which cause vomiting. They are subdivided into two groups, viz.:—

Local Emetics,—act by irritating the end organs of the gastric, oesophageal or pharyngeal nerves, and by reflex irritation of the vomiting centre. They include—Alum, Mustard, Salt, the Sulphates of Zinc, Copper and Mercury, Tepid Water in quantity, etc.

Systemic, or General Emetics,—act by direct irritation of the vomiting centre in the medulla, through the medium of the circulation. Among them are—Ipecac (Emetine), Apomorphine, Tartar Emetic, Veratrine, Senega, Squill, etc., also Opium and its alkaloids Morphine and Codeine, which cause vomiting as one of their after-effects, though ordinarily classed among the anti-emetics.

Vomiting is an evacuant act which consists in compression of the stomach by the simultaneous spasmodic contraction of the diaphragm and abdominal muscles; and relaxation of its cardiac orifice by contraction of the radiating muscular fibres in the gastric wall. If both acts occur at the same time, the contents of the stomach are expelled and vomiting occurs; if, however, the two acts do not take place simultaneously, the contents of the stomach are retained, and the abortive efforts are called retching. These acts are controlled and regulated by a nerve-centre in the medulla oblongata, which is closely connected with the respiratory centre, the muscular movements of vomiting being merely modified respiratory movements. This vomiting centre is ordinarily excited in two ways,—(1) by the peripheral stimulation of afferent nerves going to it from other parts of the body,—(2) by impulses sent down to it from the brain. (Brunton.)

Anti-emetics,—are agents which lessen nausea and vomiting, some by a local sedative action upon the end-organs of the gastric nerves, the Local Gastric Sedatives;—others by reducing the irritability of the vomiting centre in the medulla, the General Sedatives. The principal Anti-emetics are the following named substances, viz.:—

Of these the most generally efficient is Cocaine, in 6-minim doses of a 4 per cent. solution every hour by mouth, for two or three doses.

Carminatives, (carmino, I soothe),—aid in the expulsion of gas from the stomach and intestines, by increasing peristalsis, stimulating the circulation, etc. They are also diffusible stimulants. The most important members of this class are as follows, viz.:—

Cathartics, or Purgatives, (καθαιρω, purgo, I cleanse),—are agents which increase or hasten the intestinal evacuations. According to their various degrees and modes of action, they are subdivided into several groups, as follows:—

Laxatives, or Aperients,—include those which have the most moderate action, of which Sulphur is the type, the group including also Magnesia, Figs, Prunes, Tamarinds, etc.

Simple Purgatives,—cause active peristalsis, and some irritation and griping. Senna is the type of this group, its list also including Rhubarb, Calomel, Castor oil, Aloes, etc.

Drastic Purgatives,—act still more intensely, causing large watery stools, with much griping pain, tenesmus and borborygmi. Jalap is a representative drastic, and the other chief agents of the group are Colocynth, Elaterium, Scammony, Gamboge and Croton oil; all of which in large doses act as irritant poisons.

Saline Purgatives,—increase peristalsis, promote osmosis, stimulate the intestinal glands, and thus produce free, watery evacuations. The most commonly used Saline is Magnesium Sulphate, the well known "Epsom salt," but the list is a long one, including all neutral salts of metals of the alkalies or alkaline earths, such as the Potassium and Sodium Sulphates, Sodium Phosphate, Potassium Tartrate and Bitartrate, Sodium and Potassium Tartrates, etc.

Hydragogue Purgatives, (υδωρ, water),—include the most active of the drastics and the salines, those which remove a large quantity of water from the vessels. Elaterium, Gamboge, Potassium Bitartrate, and Croton oil, are the chief Hydragogues.

Cholagogue Purgatives, (χολη, bile),—stimulate the flow of bile, causing green-colored or "bilious" stools. Podophyllin is the typical cholagogue,—the others being Aloes, Rhubarb, Eonymin, Iridin, and the Mercurials.

Intestinal Astringents,—contract the intestinal vessels, diminishing the exudation therefrom and lessening the fluidity of the fecal discharges. The chief members of this class are the diluted Mineral Acids, and Acetic Acid, Lead Acetate, Silver Nitrate, Alum, Tannic and Gallic Acids, Zinc Oxide, Copper Sulphate, and the Persalts of Iron. Of these, the six last-named are the most powerful, and have a strong constringing action upon the intestinal mucous membrane, as well as their ordinary astringent action upon its vessels.

Cholagogues, and Hepatic Stimulants,—are two groups of agents which have a marked selective action upon the biliary secretion, hence the term Cholagogue, from χολη, (bile), and αγω, (I bring away). The Hepatic Stimulants increase the functional activity of the liver-cells, and the amount of bile secreted; while the Cholagogues remove the bile from the duodenum, interfering temporarily with the entero-hepatic circulation, and preventing the reabsorption of bile by the portal vessels. Some Hepatic Stimulants are also cholagogues, others are not ;—while the Cholagogues proper act indirectly as hepatic stimulants, by carrying off the bile and thereby urging the liver to secrete more. The following List includes the principal drugs in both groups.

Cholagogues and Hepatic Stimulants,—Aloes, Podophyllin, Iridin, Baptisin, Jalapin, Euonymin, Arsenic, Rhubarb, Colchicin, Colocynthin, Sodium Phosphate, Potassium Sulphate, Sodium Sulphate, etc.

Cholagogues, Mercurous Chloride, (Calomel), Pil. Hydrargyri, Mercury with Chalk, and many other mercurials.

Hepatic Stimulants,—Mercuric Chloride, (Corrosive Sublimate), Nitro-hydrochloric Acid, Nitric Acid, Benzoic Acid, Sodium Benzoate, Ammonium Chloride, Sodium Bicarbonate, Ipecac, Antimony, Guaiac, etc.

Hepatic Functions, other than the biliary, are stimulated by the following named drugs, viz.:—

The Glycogenic Function is stimulated, and the production of Glycogen increased,—by Sodium Bicarbonate, Amyl Nitrite and Nitro-hydrochloric Acid.

Urea is Increased—by Arsenic, Antimony, Ammonium Chloride, Iron and Phosphorus.

Hepatic Depressants—lower the functional activity of the liver, certain drugs acting upon certain of its functions, as follows, viz.:—

Bile-production Lessened—by Opium and Morphine, Quinine, Alcohol, Acetate of Lead, and many purgatives.

Glycogen Diminished—by Opium, Morphine, Codeine, Phosphorus, Arsenic and Antimony.

Urea Lessened—by Opium, Morphine, Colchicum, Alcohol and Quinine.

The Pancreas is stimulated to increased secretion by Ether given internally, also by galvanism of the gland itself. It is depressed by Atropine, or by any agent which induces nausea and vomiting.

Anthelmintics, (αντι, against, ελμινη, a worm),—are drugs which destroy (vermicides),or expel (vermifuges) worms inhabiting the intestinal canal. The principal vermifuges are the purgatives Castor Oil, Jalap and Scammony,—and the vermicides are classed according to the worm they are each most efficient against, thus,—

Thread-worm, (Oxyuris Vermicularis),—Alum, Ferrous Sulphate, Lime-water, Quassia, Sodium Chloride, Tannin,—all by enema.

Round-worm (Ascaris Lumbricoides),—Santonin, Spigelia, Chenopodium, Azedarach, internally,—with Senna or Calomel.

Tape-worms, (Taeniae, etc.),—Filix mas, Kamala, Cusso, Granatum, (Pelletierine), Pepo, Turpentine, Chloroform.

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