This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Comfrey root is the dried rhizome and root of Symphytum officinale, Linne (N.O. Boragineoe), an indigenous and widely distributed perennial herb. The plant produces a large erect, branching rhizome and stout, fleshy roots.
The commercial drug consists chiefly of root and occurs in pieces of varying length (often 5 to 20 mm.) and about 5 to 15 mm. thick. Externally it is deeply longitudinally wrinkled and blackish or greyish black; internally it is pale grey, brownish, or even brown in colour. It may be hard, horny or tough in consistence and exhibits a waxy surface when cut. The structure is often indistinct, but favourable pieces show a dark cork and a grey cortex separated by a greyish cambium line from an indistinctly radiate wood within which, in pieces of the rhizome, there is a circular pith. It has a slight odour and a mucilaginous taste.
Allantoin, C4H603N4, is a diureide of glyoxylic acid. It occurs in colourless, glistening prisms melting at 227°. Oxidising agents convert it into allantoic acid, C3H4N402. It is soluble in solution of sodium hydroxide, the solution evolving ammonia when heated, with simultaneous production of urea.
The drug has been used as an application to wounds, sores and ulcers, the healing action being attributed to the allantoin contained in it.