Agents Acting on the Nervous System.

Motor-Excitants,—are agents which increase the functional activity of the spinal cord and the motor apparatus, producing heightened reflex excitability, disturbances of motility, and tetanic convulsions when given in large doses,—their ultimate result being motor paralysis from over-stimulation. Such are Nux Vomica and Ignatia, with their alkaloids, Strychnine and Brucine,—also Thebaine, the tetanizing alkaloid of Opium, and Ergot, Picrotoxin, Digitalis, Pilocarpine, etc.

Motor-Depressants,—lower the functional activity of the spinal cord and motor apparatus, and in large doses paralyze them directly. The principal members of this class are Alcohol, Ether, Chloroform, Opium, Aconite, Conium, Chloral, Tobacco, Lobelia, Belladonna, Gelsemium, and Methyl-Strychnine.

Cerebral Excitants,—increase the functional activity of the cerebrum, without causing any subsequent depression or any suspension of brain-function. The chief members of this group are Camphor, Cannabis, Valerian, Caffeine, Theine, Cocaine, Tobacco, Strychnine, and Alcohol (in small doses).

Deliriants,—excite the functional activity of the higher brain to such a degree as to disorder the mental faculties, and produce intellectual confusion, loss of will power, delirium and even convulsions. They are all narcotics, though all narcotics are not deliriants. Among these agents are Belladonna, Stramonium, Hyoscyamus, Cannabis Indica, Chloral, Lupulus (at first), Opium (at first), and Alcohol (in full doses).

Cerebral Depressants,—lower or suspend the functions of the higher brains after a preliminary stage of excitement. Under this head may be included the Narcotics, the General Anaesthetics, the Hypnotics, and many of the Antispasmodics—all of which act upon the cells of the convolutions, and at first stimulating the cerebral functions, they produce after a time stupor, coma, and insensibility. The principal agents of this class are Alcohol (in large doses), Opium, Chloroform, Bromides, Chloral.

Narcotics, (narkh, stupor),—are drugs which lessen the relationship of the individual to the external world (Brunton). At first excitant to the higher brain, they soon cause profound sleep, characterized by increasing stupor,—and if the dose be sufficient, coma, insensibility, and finally death by paralysis of the centres in the medulla which govern respiration and the other functions of organic life. Narcotics are closely related to stimulants,—Alcohol and Opium being good illustrations, in the different stages of their actions, of stimulant followed by narcotic effects Such agents give us the means of lowering hyper-acute perception, of inducing sleep, and of soothing the vital functions by rest,—all of which are means of great therapeutical value. The principal narcotics are Opium, Cannabis Indica, Alcohol, Belladonna, Humulus, Chloral, Chloroform, Ether, etc.

Hypnotics, (upnoV, sleep),—are agents which, in proper doses, induce sleep, without causing deliriant or narcotic effects. Many of the most efficient hypnotics are narcotic in full dosage, the principal agents of the class being Sulphonal, Trional, the Bromides, Chloral, Paraldehyde, Cannabin Tannate, and Methylal, described under Chloral in the following pages.

Analgesics or Anodynes, (an, without, algoV, odunh, pain),—are agents which relieve pain, either by impairing the conductivity of the sensory nerve fibres, or by depressing the cerebral centres of perception and sensations. Opium does both, and hence it is the most efficient of all the analgesics. The General Anodynes act when taken internally, and affect the whole organism,—the Local Anodynes affect the part to which they are applied. some by direct depression of the terminal nerve-organs in the skin, others by reducing the local circulation. The principal agents of this class are as follows :—

General Anodynes. Local Anodynes.
Opium, Morphine. Opium.
Belladonna, Atropine. Belladonna.
Hyoscyamus, Hyoscine. Carbolic Acid.
Aconite. Cocaine.
Antipyrin. Veratrine.
Acetanilid. Aconite.
Chloral. Chloroform, etc.

Anaesthetics, (an, without, aisqhsiV, perception),—are agents which temporarily destroy sensation. The General Anaesthetics are volatile substances, which, when inhaled, produce more or less complete unconsciousness and loss of sensations, (anaesthesia), also lessened motor power. The Local Anaesthetics act similarly to the local anodynes, (see above), except that, while the latter diminish the sensibility of the part, the former destroy it entirely, for a time. The principal agents belonging to this group are the following-named :—

General Anaesthetics. Local Anaesthetics.
Ether, (Ethyl Oxide). Extreme Cold. Ice. Ether Spray or Methyl Chloride.
Methylic Ether. Carbolic Acid. Creosote.
Chloroform. Cocaine and its salts.
Methylene Bichloride. Oil of Turpentine.
Ethylene Bichloride. Hydrocyanic Acid.
Ethylidene Chloride. Veratrine.
Nitrous Oxide.

Antispasmodics, (anti, against, spasmoV, a spasm),—are agents which prevent or allay spasm of voluntary or involuntary muscles in any portion of the organism. In this group is included a long list of drugs, some of which act (1) by tonic stimulation of the nerve-centres, and thereby of the coördinating power and the circulation, others (2) by direct depression of the motor centres, and others (3) by paralyzing the end-organs of the vaso-motor nerves. A few (4) depress all the vital functions, and a large number (5) stimulate the muscular fibres of the intestines to expel gaseous accumulations. The following list includes the principal antispasmodics, the numbers referring to the special actions of each, as stated above, viz.:—

Alcohol, 1. Aconite, 4. Bromides, 2.
Ether, 1. Tobacco, 4. Amyl Nitrite, 2.
Camphor, 1. Lobelia, 4. Asafetida, 5.
Musk, 1, 5. Hellebore, 4. Cajuput, 5.
Valerian, 1, 5. Hydrocy. Acid, 4. Aromatic Oils, 5.

Coördination of Movement, or the Maintenance of the Equilibrium, is the function apparently governed by the cerebellum, and is markedly disturbed by the few drugs which specifically affect that organ, chief among them being Alcohol. In considerable doses this drug causes a staggering gait, and a tendency to fall and different preparations thereof seem to affect different portions of the cerebellum. Intoxication by wine or beer is said to be accompanied by a tendency to fall sideways,—that by whiskey, especially Irish whiskey, an inclination to fall on the face,—and that by cider, a backward tendency; and these disturbances correspond exactly with those caused by injury to different lobes of the cerebellum (Brunton). Apomorphine in large doses seems to act upon the cerebellum or corpora quadrigemina, as the animal poisoned by it does not vomit, but moves round and round in a circle.

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