Habitat
It is found throughout India ascending upto 1,800 m. in the Himalayas, and in the Andaman and Nicobar Islands.

Morphology Description (Habit)
At least two types of O.tenuiflorum are encountered with in cultivation; the green type (Sri tulasi) is the most common; the second type (Krishna tulasi) bears purple leaves.The plant is an erect, herbaceous, much-branched, softly hairy annual. The leaves are elliptic-oblong, acute or obtuse, entire or serrate, pubescent on both sides and minutely gland-dotted; the flowers are in close whorled racemes, purplish or crimson. The nutlets are sub-globose or broadly ellipsoid, slightly compressed, nearly smooth, pale brown or reddish and show small black markings.

Principal Constituents
A bright yellow volatile oil. Besides the volatile oil, the plant is reported to contain alkaloids, glycosides, saponins and tannins. The leaves contan ascorbic acid and carotene1.The major constituents of the essential oil from the plant, investigated in Germany, are: 1,8-cineole, 5.6-11.0; E-ß-ocimene, 4.0-4.7; ß-Caryophyllene, 1.4-2.5; a-humulene, 2.0-3.5; methylchavicol, 11.6-14.4; germacrene-D, 2.4-4.5; ß-bisabolene, 7.6-15.4; a-bisabolene, 9.4-19.6; and eugenol, 24.2- 38.2%2.

Pharmacology
The ethanol extract (90%) of the leaves also showed hepatoprotective effect against paracetamol-induced liver damage in rats. Oral administration of the alcoholic extract of the leaves lowers blood sugar level in normal, glucose-fed hyperglycemic and streptozotocin- induced diabetic rats. The extract improves glucose tolerance and potentiates the action of exogenously injected insulin. The activity of the extract was 91.55 and 70.43% of that of tolbutamide in normal and diabetic rats, respectively. The ethanolic extract (50%) of fresh leaves, volatile oil (from fresh leaves) and fixed oil (from the seeds) has shown anti-asthmatic activity and has significantly protected guinea pigs against histamine and acetylcholine induced pre-convulsive dyspnea. These extracts/oils also showed anti-inflammatory activity and inhibited the hindpaw edema in rats against carageenan, serotonin, histamine and PGE-2 induced inflammation. The effect of ursolic acid, a triterpene from the leaves, in the allergic process has been evaluated employing rat peritoneal mast cells and by estimating the changes in the release of histamine induced by compound 48/80. Ursolic acid exhibited a significant protection of the mast cell membrane by preventing degranulation and decreased the quantity of histamine released by compound 48/80. The essential oil from the leaves has shown significant antipyretic activity in Brewer's yeast-induced pyrexia in rats. The leaf extract is found effective in checking the protease activity of the dermatophyte, Trichophyton, at 50% concentration3.

Clinical Studies
In a preliminary clinical trial, on 16 patients suffering from viral encephalitis, the aqueous extract of O.sanctum leaves has been reported to lead to a higher survival rate of patients than that in a steroid treated group of ten patients. The incidence of residual neurological deficit in a period of one month was reported to be low in the extract treated patients4.

Toxicology
The LD50 of the leaf extract in mice was 3.75g/kg i.p.

1. Uphof, 251; Chem. Abstr., m 1954, 48, 11728; Basu et. al., J. Indian chem. Soc., 24, 358.
2. Laakso et. al., Planta Med, 1990, 56, 527.
3. De et. al., Indian Drugs, 1993, 30, 355; Chattopadhyay, Indian J Exp Biol, 1993, 31, 891; Singh & Agrawal, J Res Educ Ind Med, 1991, 10 (3), 23; Singh & Agrawal, Int J Pharmacogn, 1991, 29, 306; Rajasekaran et. al., Indian J Pharmacol, 1989, 21 (1), 21; Tandon et. al., Indian J Pharm Sci, 1989, 51(2), 71; Iyer & Williamson, Geobios, 1991, 18(1), 3.
4. Das et. al., Antiseptic, 1983, 323.