Active Ingredients. - The recent and outermost part of the rind of the fruit has an aromatic and bitter taste; the odor is strong and peculiar. These qualities depend upon the presence of a volatile oil, which, when pure, is colorless or pale yellow, limpid, fragrant, and possessed of a warm and bitter taste. It is soluble in anhydrous alcohol; less so in rectified spirit. The composition is C10H16 - that is to say, it is isomeric with the oils of turpentine, savin, juniper, and copaiva. The juice of the fruit consists of citric acid (H3C6H5O2H1O, sp. gr. 1:039), malic acid, gum, bitter extractive, and water. Of these substances the citric acid, of which there are about thirty-two grains in every ounce of lemon-juice, is the most important. It occurs in colorless crystals, of which the right rhombic prism is the primary form, and which are very soluble in water, less soluble in rectified spirit, and insoluble in pure ether.

Physiological Action. - Oil of lemon-peel is stimulant, carminative, and diaphoretic, and hence becomes a grateful stomachic. Applied externally, it is stimulant and rubefacient. The juice of the ripe fruit is refrigerant and antiscorbutic; and similar but much feebler properties pertain to citric acid. The juice also, dissolved in water, is employed as a beverage. It allays thirst, diminishes preternatural heat, abates undue perspiration, and quickens the action of the kidneys.

Therapeutic Action. - The chief employment of oil of lemon-peel is as a carminative, but it is generally used in connection with medicines of more energy, and appears to have its chief value in dyspepsia.

Rheumatism. - Lemon-juice has been recommended as a remedy in acute rheumatism and in gout, and has been successfully employed in England, France, Italy, and the United States. At present, however, it is not looked upon with the same confidence with which it was regarded by its introducer, Dr. Owen Rees. Its effects are about the same as those of a mild alkaline treatment.

Narcotic poisoning. - Lemon-juice is valuable also in cases of poisoning by narcotic substances such as opium. In these, after the poison has been removed from the stomach, the effects may be partly counteracted by the free use, either of the juice of the fruit, or of citric acid in solution.

Scurvy. - By far the most important use of lemon-juice is its employment in scurvy. Lemon-juice and lime-juice, the latter more especially, have been adopted, as the result of frequent and striking experience, as the most convenient and perfect prophylactic and curative in sea scurvy; and, as such, lime-juice is ordered to be constantly carried in stock by the ships both of the Royal Navy and of the merchant service.

But it has long been known that no substance peculiar to the lemon is needed for the prevention and cure of scurvy: and especially, it has been completely proved that citric acid is by no means the only antiscorbutic. Given alone, citric acid has proved but feebly curative. It has also been found that a number of other fruits and vegetables1 are antiscorbutic, always provided that their juices are in a fresh, state. So markedly is this the case that a theory was once set up, the very contrary of that which placed the cure to the score of the acid, attributing the antiscorbutic action to the citrates and malates of potash which the juices contain. This theory, however, has proved no more stable than the other; and at present it can only be said that various fruits and vegetables are both prophylactic and curative in scurvy, and that lemon-juice is a very convenient form in which to administer this kind of corrective, because easily preserved by the addition of a small proportion of spirit (10 per cent.).

As a perfume, oil of lemon is an exceedingly useful adjunct to sulphur ointment and to evaporating lotions.

Lemon-juice, converted into "lemonade," is of great service in febrile and inflammatory complaints, and in hemorrhages.

Combined with bicarbonate of potash, it forms a citrate of potash, which is a mild diaphoretic and diuretic, and often allays restlessness and watchfulness in fever.

It is adapted, also, for lithic acid deposits, but is sometimes objectionable in phosphatic ones.

Preparations and Dose. - Limonis succus, 3 ss. - 3 i. (15. - 30.); Syrupus Limonis, as a vehicle; Mistura Potassii Citratis, 3 ss. - ij. (15. - 60.).