Rhei Radix-Rhubarb Root.-The dried root deprived of the bark, from one or more undetermined species of Rheum. From China. Chinese Tartary, and Thibet. Imported from Shanghai and Canton.

Characters.-Trapezoidal, roundish, cylindrical, or flattish pieces, frequently bored with one hole, yellow externally, internally marbled with fine waving greyish and reddish lines, finely gritty under the teeth; taste bitter, faintly astringent and aromatic; odour peculiar.

Composition.-The active purgative principle of rheum is probably identical with cathartic acid, the purgative constituent of senna. With this is combined rheo-tannic acid, possessing astringent properties. The yellow colouring matter is chryso-phanic acid in small quantity; now made from araroba, and used for other purposes. (See page 231.) Chrysophan, C16H1808, is a yellow crystalline bitter glucoside. Emodin, phceoretin, and oxalate of lime (35 per cent.) are less important constituents.

Impurities.-English rhubarb, known by taste, odour, and excess of starch. Turmeric, reddened by boracic acid.

Dose.-As a stomachic, 1 to 5 gr.; as a purgative, 10 to 20 gr.

Preparations.

1. Extractum Rhei

Extractum Rhei. Spirituous. 100 in 39. Dose, 3 to 10 gr.

2. Infusum Rhei

Infusum Rhei. 1 in 40. Dose, 1 to 2 fl.oz.

3. Pilula Rhei Composita

Pilula Rhei Composita. Rhubarb, 3 oz.; Socotrine Aloes,

2 1/4 oz.; Myrrh, 1 1/2 oz.; Hard Soap, 1 1/2 oz.; Oil of Peppermint, 1 1/2 fl.dr.; Treacle, 4 oz. Dose, 5 to 10 gr.

4. Pulvis Rhei Compositus,-" Gregory's Powder." Rhubarb,

2 ; Light Magnesia, 6; Ginger, 1. Dose, 1/2 to 1 dr.

5. Syrupus Rhei

Syrupus Rhei. Dose, 1 to 4 fl.dr.

6. Tinctura Rhei

Tinctura Rhei. 1 in 10. Dose, as a stomachic, 1 to 2 fl.dr.; as a purgative, 1/2 to 1 fl.oz.

7. Vinum Rhei

Vinum Rhei. 1 in 14. Dose, 1 to 2 fl.dr.

All preparations, excepting the Extract and Infusion, are compound.

Action And Uses. 1. Immediate Local Action And Uses

The action of rhubarb is confined to the alimentary canal. In small doses (1 to 5 gr.), the bitter principle and rheo-tannic acid are chiefly active, as bitter stomachics and intestinal astringents. In larger doses (up to 40 gr.) the cathartic acid exerts its influence before the rheo-tannic acid; stimulates the intestinal movements and liver, as in senna, with some griping; and causes purgation, producing in six to eight hours a liquid motion, of a yellow colour from the pigment of the rhubarb and excess of bile. The cathartic acid being expelled, the effect of the tannic acid becomes evident, and the bowels are confined.

Rhubarb is used in small doses as a bitter stomachic, intestinal astringent, and tonic, to correct atonic indigestion with diarrhoea, as in dyspeptic and rickety infants and children. Larger doses are given as a purgative, in the form of the Compound Powder, to sweep out the bowels and then set them at rest, in cases of summer diarrhoea and diarrhoea ab ingestis of children, combined sometimes with a mercurial. The Compound Pill is a familiar mild laxative for habitual use, suiting some persons, but demanding constant repetition in the majority. The cholagogue action of rhubarb adds to its value both in stomachic and purgative preparations. Its griping effect must be remembered, and the drug should never be given alone.

3. Action In The Blood, Specific, And Remote Local Action

The chrysophan and chrysophanic acid, at least, are absorbed into the blood, pass through the tissues, and are thrown out in the secretions, which they stain yellow, including the urine.