Origin. - A fixed oil compressed from the seed of Ricinus communis L., a plant indigenous in Southern Asia and cultivated in temperate countries for ornament and other purposes, remaining a large annual.

Description and Properties. - A pale-yellowish or almost colorless, transparent, viscid liquid, having a faint, mild odor and a bland, afterward slightly acrid and generally offensive taste. Soluble in an equal volume of alcohol and all proportions in absolute alcohol. Castor oil should be kept in well-stoppered bottles.

Dose. - 1/4-2 fluidounces (8.0-60.0 Cc.) [4 fluidrams (16 Cc), U. S. P.].

Physiological Action. - Externally and Locally. - Castor oil -like other bland fixed oils, such as almond oil, olive oil, etc. - is sedative and protective when applied to the skin or mucous membranes.

Internally. - The only important action is upon the intestinal tract, on which the oil acts as a mild irritant, causing purgation. Chemically castor oil is a combination of glycerin, fatty acids, and ricinoleic acid. This combination goes through the stomach unchanged, but in the presence of the bile and pancreatic juice it is broken up into glycerin and ricinoleic acid; the ricinoleic acid combines with sodium and forms sodium ricinoleate, which has marked irritating properties. The ricinoleate of sodium is absorbed and excreted in various ways, appearing in the mother's milk and imparting to it purgative properties.

Castor oil requires from four to six hours to operate, its action being usually attended with little pain. It causes a large, soft stool and usually empties the entire intestinal canal.

The poisonous principle, ricin, found in the seed-coat of castor oil beans, is an albuminous substance belonging to the globulin group, and is generally termed a toxglobulin. Ricin, is one of the most powerful poisons known, but being insoluble in oil and soluble in water it is not present in expressed castor oil. The symptoms of poisoning from castor beans are violent abdominal pain, vomiting, purging, and collapse. Postmortem examinations have revealed evidences of severe inflammation in the stomach and intestines, with capillary thrombi in various organs.

Castor oil should not be used as an habitual laxative, its continual employment being liable to occasion constipation with all its attendant evils.

Therapeutics. - Castor oil is used alone or associated with balsam of Peru as a sedative protectant dressing for superficial ulcerations. The drug is also serviceable in various diseases of the skin and mouth.

It is probably superior to all other laxatives, and is applicable to all conditions for which laxatives are employed. In large doses it is one of the best purgatives to give in conjunction with an anthelmintic.

Administration. - The unpleasant taste of castor oil is the only objection to its use. Yet it can be rendered quite palatable by mixing it with a small quantity of glycerin, to which may be added a few drops of oil of cinnamon or oil of wintergreen.

Various other devices for disguising the taste have been adopted, such as enveloping the oil in the froth of beer, ale, or porter, or washing out the mouth with brandy or whisky previous to administration, and allowing the patient to swallow the oil quickly, when it will not adhere to the mouth and fauces, especially if followed by a drink of some alcoholic liquid.

In the form of an emulsion the taste of the oil is well disguised. There are also soft capsules of castor oil which are, of course, tasteless, yet they are too bulky to be popular.

Castor-oil emulsion may be used as an enema when a mild injection is required.