The dried rhizome and rootlets of Arnica montana. Collected in the mountainous parts of middle and southern Europe.

Substances resembling Arnica: Valerian, known by smell; Serpentary, with very many contorted rootlets; Veratrum Viride, with thicker rootlets.

Characters.-Rhizome from one to three inches long, and two or three lines thick, cylindrical, contorted, rough from the scars of the coriaceous leaves, and furnished with numerous long slender fibres ; has a peppery taste and peculiar odour.

Composition.-The pharmacology of arnica is still obscure. It contains a small quantity of volatile oil, of complex composition, and said to yield trimethylamin; tannic acid ; and a bitter substance, arnicin.

Preparation.

Tinctura Arnicae.-1 in 20. Dose, 1 to 2 fl.dr.

Action And Uses. 1. Immediate Local Action And Uses

Externally.-Arnica, applied to the skin, sometimes causes hyperaemia, eczema, and even spreading erysipelas. It would, therefore, appear to increase the activity of the circulation in the skin ; and the tincture in water is a popular application to bruises, preventing swelling, and hastening the absorption of effused blood. It must be used with caution.

Internally.-Arnica is a stimulant to the alimentary canal, like volatile oils in general; in over-doses a powerful irritant, causing vomiting, pain, and purging, with consequent constitutional effects. Probably by reflex action from the stomach (see Caryophyllum, page 242) it stimulates the heart and circulation, the brain and spinal cord, in moderate doses ; the pulse being strengthened, and symptoms of nervous debility removed. Arnica has, therefore, been used with success in low forms of fever, delirium tremens, and mental disorder.

2. Action On The Blood, And Specific Action And Uses

The active principles of arnica enter the blood and thence the tissues, where its effects somewhat resemble those of turpentine. If the dose be considerable, the reflex stimulant effect from the stomach is overcome by its depressing action on the circulation and nerve centres ; headache, unconsciousness, and convulsions being induced, and the body temperature lowered. Arnica has thus been employed as an antipyretic, especially in acute rheumatism, but cannot be said to be used now.

3. Remote Local Action And Uses

Like its allies, arnica is a remote stimulant of the kidneys and skin, and has been given in some cutaneous diseases such as eczema, and in chronic rheumatism.