A volatile oil distilled from the fresh leaves of Eucalyptus globulus, or Eucalyptus amygdalina, and some other species of Eucalyptus.

Characters. - A colourless or very pale yellowish liquid, having a characteristic aromatic odour, a pungent, spicy, and cooling taste, and a neutral reaction. It is soluble in an equal weight of alcohol.

Dose. - 1 to 4 minims. B.P.

B.P. Preparation.

Unguentum Eucalypti (Oil of Eucalyptus, 1; hard paraffin, 2; soft paraffin, 2).

Action. - Eucalyptus oil, or eucalyptol, as it is often termed, is a powerful antiseptic, even more powerful than quinine (p. 95). The antiseptic action of the oil is greater when it is old and charged with oxygen than when it is freshly distilled. Like quinine (p. 62) it arrests the movements of white blood-corpuscles, and its vapour prevents inflammation in the exposed mesentery of the frog. The red corpuscles of frog's blood have their nucleus rendered more distinct, and their surface wrinkled by it. Like quinine it causes contraction of the spleen. It is a local irritant. When applied to the skin and its evaporation prevented, it acts as a rubefacient, vesicant, or pustulant. When applied to a mucous membrane or injected hypodermically it causes pain. When swallowed it causes burning in the throat, stomach, and intestine. It may produce nausea, loss of appetite and slight looseness of the bowels, but it is not an active emetic, nor purgative. In large doses after absorption it appears to act chiefly on the nerve-centres, producing paralysis and death. In invertebrata killed by exposure to its vapour the paralysis is preceded by excitement, but in vertebrate animals the paralysis is not preceded by excitement. Its depressing action on the spinal cord is so great as to abolish reflex action even when it has been previously increased by brucine; and from depression of the brain, medulla, and heart, there is drowsiness, feeble respiration, lowered blood-pressure and fall of temperature. Death occurs from paralysis of the respiration. It is excreted by the lungs and kidneys. Like turpentine it imparts a smell of violets to the urine of persons taking it.

Uses. - It has been employed as an antiseptic in surgical dressing in the form of eucalyptus gauze, but is apt to cause local irritation. It has proved useful as a lotion to wash out suppurating cavities. As an inhalation it has been employed to check secretion, and remove foetor in ozaena, in bronchitis with profuse or foetid expectoration, in phthisis and in diphtheria. It has been used in the form of injections or pessaries in uterine catarrh, and after parturition. It has been recommended as a hypodermic injection in pyaemia.

In three cases of septicaemia I treated by it recovery occurred during its use, and in one of these quinine had proved useless. It has been used as an antiperiodic in ague and an antipyretic in fever, but it has not proved so useful as one would have expected from the resemblance between its action and that of quinine.

Eucalyptus trees when freely planted in malarious districts appear to render them more healthy.