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 as a stimulant-narcotic in Peru and Bolivia. Small doses excite the nervous system, while larger doses are depressing. The chief action of cocaine from a practical point of view is its power of paralysing the terminations of sensory nerves.

5. Atropine, hyoscyamine, homatropine, duboisine, daturine and some other bodies have a paralysing action upon the ends of the motor and secretory nerves. They therefore lessen all the secretions, and among other actions dilate the pupil and increase the rapidity of the heart by paralysing the vagus. In addition they have a stimulating action on the central nervous system.

6. Nicotine, piturine and lobeline are the active principles of tobacco and other substances which are smoked as stimulant narcotics. In large doses they are powerful nerve poisons, but as usually taken they exercise a gently stimulant effect upon the nervous system. Pilocarpine has an action closely allied to that of nicotine, but as it is much less poisonous (the effects produced by small doses being chiefly excessive sweating and salivation), it is capable of being utilized in medicine. Muscarine has a very close resemblance in action to pilocarpine.

7. Physostigmine, the active principle of the Calabar bean, acts chiefly as a stimulant to voluntary and involuntary muscles, and at the same time exercises a depressing effect upon the spinal cord. It contracts the pupil.

8. Conine, gelseminine and sparteine all exert a paralysing effect on the terminations of the motor nerves, to the implication of which the weakened gait and other symptoms are due.

9. Aconitine, delphinine and many of their derivatives have a very widespread depressing action on muscle and nerve.

10. Apomorphine is essentially a muscle poison, but owing to the fact that minute doses stimulate the vomiting centre and cause emesis before any other symptoms are observable, its emetic action is the most prominent effect in man.

11. Emetine acts as a gradual depressant to the nervous system in animals. In man its chief effect is its emetic action, which seems to be due entirely to local irritation of the stomach.

12. Quinine. Several of the other alkaloids found in cinchona bark act very much like quinine. They all depress the conducting power and the grey matter of the spinal cord, and to a much less extent that of the brain. They lessen the general metabolism and lower febrile temperature. The cinchona alkaloids have a specifically poisonous effect on the parasites of malaria when present in human blood, and are poisonous to all low organisms.

13. Phenacetin, acetanilide, phenazone and many similar bodies act as antipyretics in virtue of an action on the heat-regulating centres in the cerebrum.

Digitalis.—This group-name has been given to a large number of substances which have an action similar to that of the foxglove leaves, including the active principles of strophanthus, squill, Urechites suberecta, Convallaria majalis, Nerium Oleander, Helleborus niger, Antiaris toxicaria (the upas tree), and several others. The active principles of these vary a good deal in chemical composition, but they are all non-nitrogenous neutral bodies. Their action is exerted upon muscle, and chiefly upon the muscle of the heart and blood vessels. The individual muscle-fibres contract and expand more perfectly, and thus the diastole and systole of the heart are rendered more complete, the pulse is slowed, and the blood-pressure is raised. The slowing of the heart is partly brought about by an action on the vagus centre.

Picrotoxin.—In large doses the action of picrotoxin is exerted chiefly on the medullary nerve centres, whereby irregular tonic-clonic convulsions are produced; in minute doses it stops the secretion of sweat.

Saponin.—Saponin and many allied bodies form an abundant soapy-looking froth when shaken up with water, and they are contained in a very large number of plants, the chief of which are the Quillaia saponaria, Polygala senega, sarsaparilla, and others, known collectively as soapworts. They all act as local irritants in the alimentary canal, and after absorption are more or less depressing to the muscular and nervous systems. They produce slight nausea and increased secretion of mucus.

Cyanogen.—This includes compounds of cyanogen such as hydrocyanic (prussic) acid, cyanides of potassium, sodium, &c., cherry-laurel water, amygdalin, bitter almonds and other chemical and vegetable substances which readily yield hydrocyanic acid. Hydrocyanic acid is a general protoplasmic poison, all the lower organisms being very susceptible to its action, while in the higher animals it speedily depresses or paralyses all forms of nerve tissue. It enters into combination with haemoglobin, forming a bright scarlet compound and interfering with respiration. It kills by its paralysing effect on the motor ganglia of the heart and on the respiratory centre.

Ferments.—These include such bodies as pepsin, diastase, the pancreatic ferments, papain, the pine-apple ferment, taka-diastase and others, and serve to convert starch into saccharine substances, or albumen into peptone and albumoses.

Animal Glands and Secretions.—Of these the thyroid gland, the suprarenal bodies, the spleen, the bile, the bone marrow, the ovaries and some others have been investigated fully. Speaking generally, when given in small doses their action on the

healthy organism is slight or nil, but in disease some of them are capable of acting as substitutes for deficient secretions.

Antitoxins.—These are substances which antagonize the toxins formed in the body by pathogenic organisms, the toxins of snake venom and other animal poisons, and vegetable toxins such as abrin, ricin, &c. A healthy person can be rendered insusceptible by gradually accustoming him to increasing doses of these poisons, and this immunity is due to antitoxins which are found in the blood-serum and which are products of the blood cells. The nature of these antitoxic substances is not definitely known, but they combine with and destroy the poisons. In specific germ diseases a similar antitoxin forms, and in cases which recover it counteracts the toxin, while the germs are destroyed by the tissues. Antitoxins can be prepared by immunizing a large animal, such as a horse, by injecting gradually increasing doses of specific toxins into its subcutaneous tissue. In due time the horse is bled, the serum is filtered free of blood corpuscles, and then constitutes the antitoxic serum, which can be standardized to a certain potency. Such serums are injected subcutaneously in diphtheria, tetanus, streptococcic infections, plague, snake-poisoning, cholera and other similar diseases. They do not as a rule harm healthy men even in large quantities, but when repeated they often cause serious symptoms due to the body becoming more sensitive to the action of the horse-serum in which they are contained.

Neutral Fats.—This includes cod-liver oil, almond oil, olive oil, lard, &c., all of which act as foods when taken internally, and have a merely physical emollient action when applied externally. Lanolin, linseed oil, wax, spermaceti, &c., also belong to this group. The paraffins, glycerin and vaseline, although not fats, have much the same effect when applied externally, but they are not nutritive.

Sugars, Starches, Gums, Gelatin, &c..—Although these and allied bodies are used in various ways as remedies, their action is for the most part purely mechanical or dietetic.

.—T. Lauder Brunton, Pharmacology, Therapeutics and Materia Medica (3rd ed., London, 1891); The Action of Medicines (London, 1897); H. C. Wood, Therapeutics: its Principles and Practice (10th ed., London, 1905); A. Cushny, A Textbook of Pharmacology and Therapeutics (1906); C. D. F. Phillips, Materia Medica, Pharmacology, and Therapeutics (Inorganic Substances) (London, 1894); Binz, Lectures on Pharmacology (Trans., New Sydenham Society, London, 1895); Schmiedeberg, Grundriss der Arzneimittellehre (3rd ed., Leipzig, 1895, Eng. trans. by Thos. Dixon, Edinburgh, 1887); Stokvis, Leçons de pharmacothérapie (Haarlem and Paris, 1898); Rabuteau, Traité de thérapeutique et de pharmacologie (Paris, 1884); Vulpian, Les Substances toxiques et medicamenteuses (Paris, 1882); J. Harley, The Old Vegetable Neurotics (London, 1869); J. Mitchell Bruce, Materia Medica and Therapeutics; W. Hale White, Materia Medica, Pharmacy, Pharmacology and Therapeutics (London, 1909); Walter E. Dixon, A Manual of Pharmacology (London, 1906).

It may be useful to give here a general explanation of the common names used in the therapeutic classification of drugs. It is convenient to divide drugs and other substances used in medicine into groups according to the part of the system on which they chiefly act, though, as stated above, many drugs act in more than one manner and could come under several groups.

I. Drugs acting on the blood vessels, which either dilate the vessels when taken internally or applied locally, or contract the superficial arterioles. Irritants (Lat. irritare, to excite) include: Rubefacients (Lat. rubefacere, to make red), which cause the skin to become red from dilatation of the blood vessels; Vesicants (Lat. vesica, a bladder), which irritate sufficiently to cause the blood-serum to exude and form vesicles or blisters, e.g. cantharides; Pustulants (Lat. pustula, a blister), still more powerful in their effects, causing the blisters to become filled with pus, e.g. croton oil. Escharotics (Gr. , hearth, brazier; hence mark of a burn, “scar”) or Caustics (Gr.  , to burn), cause the death of the part, e.g. silver nitrate and nitric acid. The term counter-irritant is used when an irritant is applied to the skin for the purpose of relieving pain or congestion by dilating the superficial vessels. Drugs which contract the vessels and diminish exudation comprise Astringents (Lat. astringere, to draw close), while Styptics (, to contract) or Haemostatics (Gr.  , blood,  , causing to stand) are substances applied either locally or internally in order to arrest bleeding; cold, adrenalin, ergot and the per-salts of iron may be taken as examples.

II. Drugs acting on the digestive tract. Sialogogues (Gr. , spittle,  , leading) increase the flow of saliva, e.g. mercury; Antisialogogues decrease the flow, e.g. belladonna. Aromatics (Gr. , spice) or Bitters increase the flow of the gastric juice. Stomachics (Gr.  ) have the same effect. The term Carminatives (Lat. carminare, to card wool), adopted from the old medical theory of humours, is generally applied to pungent substances which help to expel gas from the stomach by stimulating the movement