This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
Castor Bean and Castor Oil, Ricinus Communis. The beans are official in four countries, the oil universally so. Castor oil is the glycerine ester of ricin-oleic acid; its purgative properties are due to the liberation of the acid. It increases the rate of peristalsis in the small intestine. For a discussion of Turin, the toxic agent of the bean, see "Pollen Extracts." No ricin is found in the oil, the unpleasantness of which is due more to the odor than to the taste. Castor oil is inert in the acid stomach and does not become purgative until it reaches the intestine. It is absorbed from the intestine, like the nutritive oils. The oil is not toxic, even in large quantity; the beans may give rise to a fatal gastro-enteritis marked by collapse. The leaves, applied to the breasts, are said to be galactagogue.
A mild and much esteemed laxative without side-action. It is the post-partum laxative, is very slightly irritating to hemorrhoids, and is much valued as a laxative for children. With Peruvian balsam, it is used as a surgical dressing. Do not give with teniafuges soluble in oils.
Average dose of the oil, 4 fluidrachms.