An alkaloid obtained from Belladonna Root.

Source.-Made by the following process: (1) Exhausting the root with Spirit; (2) precipitating the colouring matters with Lime, and filtering, and neutralising excess of Lime with Sulphuric Acid; (3) distilling off Alcohol, substituting Water, and thus precipitating (a) the resins and (b) the Atropia; (4) removing the Atropia by solution in Chloroform, distilling off the latter, dissolving in Spirit, purifying with Charcoal, and crystallising.

Characters.-Colourless, or white acicular crystals. Sparingly-soluble in water, more freely in alcohol and ether. Readily decomposed in solution. Alkaline, readily forming crystallisable salts with acids. It can he chemically resolved into tropin and tropic acid; and reconstructed by the synthesis of these bodies. One of the products of tropin, called homatropin, has been used as a mydriatic instead of atropia. The intimate cause of the isomerism but non-identity of atropia with the other alkaloids of the atropaceae has yet to be discovered.

Incompatibles.-Caustic alkalies decompose it; e.g. Liquor Potassae (often prescribed with belladonna) renders it inert. Opium, physostigma, and strychnia are in various respects and degrees physiological antagonists. See Opium, pages 192 to 197.

Preparations.

a. Liquor Atropiae.-4 gr. to 1 fl.oz. of Water and Spirit. Not given internally..

b. Unsruentum Atropiae.-8 gr. in 1 oz.

From Atropia is made:

Atropiae Sulphas.-Sulphate of Atropia. Source.-Made by dissolving Atropia in Diluted Sulphuric Acid and Water, and evaporating. Characters.-A colourless powder, very soluble in water and in spirit; neutral. Dose, 1/120 to 1/60 gr., but not given internally as such.

From Atropioe Sulphas is prepared: a. Liquor Atropiae Sulphatis.-4 gr. to 1 fl.oz. of Distilled Water. Dose, 1 to 2 min., by the mouth; or 2 to 5 min. of a mixture of equal parts of the Liquor and distilled water, hypodermically.

Action And Uses. 1. Immediate Local Action And Uses

Externally.-Belladonna and atropia, as such or in aqueous suspension or solution, are not absorbed by the unbroken skin, but alcohol, chloroform, camphor, and glycerine, with which they are generally combined, readily convey the atropia through the epidermis. Exposed mucous membranes and inflamed areas of skin still more readily absorb atropia.

Belladonna depresses the sensory nerve endings, thus acting as a local anaesthetic and anodyne; the blood-vessels are first somewhat contracted, and then relaxed; and the motor nerve filaments to underlying muscles reduced in activity. Any other special nerve endings, with which the atropia may come in contact, are similarly depressed, e.g. the nerves of the sweat and mammary glands.

Belladonna is used locally as liniment, plaster, ointment, and atropia more rarely in ointment, to relieve the pain and spasm of muscular rheumatism and neuralgia (less useful); as an anodyne and antiphlogistic in acute gout, boils, erysipelas, and other superficial inflammations-in all of which Glycerine of Belladonna (equal parts of the extract and glycerine), freely smeared on, is of great service; and in prurigo and other skin diseases to relieve itching.

Internally.-The action of belladonna on the mouth is not a local but specific one, to be presently described. In the stomach it produces a slightly anodyne effect, and has been used to relieve some forms of gastralgia and sickness. Its action on the bowels is also specific, as will be seen.

2. Action In The Blood

Atropia very rapidly enters the blood as such, and leaves it for the tissues. As far as is known, it does not alter the corpuscles.

3. Specific Action

Atropia reaches the organs with remarkable rapidity, and sets up a train of characteristic phenomena. After moderate doses of an active preparation of belladonna, patients almost invariably complain of dryness in the throat, with difficulty of swallowing; the pupils are found to be dilated, the vision confused; the balance and gait uncertain; the bowels possibly relaxed; the pulse reduced in frequency; the conjunctiva and even the face flushed. Larger doses aggravate these phenomena, but the pulse now becomes frequent instead of the reverse; restlessness or even convulsions may occur; and the patient becomes delirious. These symptoms occasionally follow the incautious application of belladonna to wounds or erupted areas of skin.

Physiological analysis of these phenomena yields the following results:

Convolutions.-The delirium caused by belladonna is rarely seen after medicinal doses. It is followed by dulness, somnolence, and insensibility, all evidences of cerebral depression.

Spinal cord.-Belladonna acts by no means powerfully on the cord, beyond slightly increasing and afterwards diminishing its reflex irritability.

Medulla.-The three great vital centres in the cord are markedly affected. The respiratory centre is powerfully stimulated by belladonna, so that the movements of the chest become more frequent and more deep. This effect is independent of the blood pressure. Poisonous doses paralyse the same centre. The cardiac centre is for a time stimulated and the heart slowed. This is but a small part of the effect on the heart, as will be immediately seen. The vaso-motor centre is first stimulated and then depressed by belladonna: that is, the systemic arteries are contracted and the blood pressure raised for a time; afterwards the vessels relaxed, and the pressure lowered, causing the flushing of the skin. The irritability of the motor nerves is diminished, but not lost, except after large doses. The voluntary muscles remain unaffected. The sensory nerves, which, as we have seen, are locally depressed, are also depressed specifically. Thus pain is prevented or relieved.

Special efferent nerve terminations.-A markedly depressing action is exerted by belladonna upon the terminations of certain special motor or secretory nerves in connection with the viscera, or upon the "terminal apparatus" between these fibrils and the active protoplasm.