This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This is the root of Curcuma longa, a small perennial plant, indigenous in the East Indies and Cochin China, and abundantly cultivated in various parts of Southern Asia. There are two varieties, both produced by the same species of Curcuma, but distinguished by their shape, one being long, and the other round, and therefore named curcuma longa and curcuma rotunda. The former, or long turmeric, is much more abundant in the market than the latter. It is cylindrical, about as thick, but generally not quite so long, as the little finger, tuberculated, and somewhat contorted. The latter, or round turmeric, is round or oval, about the size of a pigeon's egg, or somewhat larger, and marked externally with numerous annular wrinkles. Both are yellowish on the outside, and of a deep orange-yellow within, compact, hard, exhibiting when broken a wax-like fracture, and yielding a yellow or orange-yellow powder. Turmeric has a peculiar aromatic odour, and a warm, bitterish, somewhat aromatic taste, and tinges the saliva yellow when chewed. Its medical properties probably reside exclusively in a volatile oil, which is yellow and acrid. It contains, however, another interesting principle, denominated curcumin, on which its colouring properties, and its use as a chemical test, depend. (See U. S. Dispensatory.) It formerly had some reputation as an aromatic, resembling ginger in its action on the system, though less efficient, and also less agreeable. It was also supposed to have a special influence upon the biliary organs, probably from its yellow colour, and was used in jaundice and visceral disease. At present, it is scarcely used as a medicine, and probably never in this country. As a condiment, however, it is largely consumed in the East, entering into the composition of most of the curries so much in favour there. Its chief use here is as a test for alkalies, which change its yellow colour to brown. For this purpose it is employed in the form of tincture, or of turmeric paper. The powder might be exhibited in the dose of from ten to thirty grains.