128. The white and purple varieties of Datura are common on waste places throughout India; they possess the same medicinal properties, and although the purple variety is generally regarded as the more powerful, there is no evidence of its being so. Although a valuable medicine, _much caution is necessary in its employment; as in over-doses it acts as a powerful narcotic poison_. A very useful preparation is a tincture made by macerating two and a half ounces of bruised Datura seeds in one pint of proof spirit (356) for seven days in a closed vessel, occasionally shaking; it should then be pressed, and filtered, and measured, and sufficient proof spirit added to make one pint. This tincture generally produces all the sedative and narcotic effects which could be expected from opium, besides effecting a great saving, opium being very expensive, whilst this tincture can be prepared at a comparatively small cost. The dose requires to be regulated in each individual case; it is better, therefore, to commence with small doses of ten or twelve drops in a little water, and increase them to twenty or thirty drops, according to circumstances. As a general rule, twenty drops will be found to be equal in effect to one grain of opium. One of the effects of Datura is to produce dilatation of the pupil; the eye should therefore be occasionally examined whilst this remedy is being administered, and should the pupil be found very large and dilated, it may be regarded as a sign that the medicine has been carried as far as it can be _with safety, whether it has produced its other intended effects or not_. 128β. In Datura we have an excellent, if not perfect, indigenous substitute for Belladonna [Atropa Belladonna, _Linn._, is an indigenous shrub, in the Western Temperate Himalaya, alt. six to eleven thousand feet; from Kashmir to Simla (Flora British India), and the Kuram Valley, _Aitchison_]—in the treatment of _Cataract and other Diseases of the Eye_. Its mydriatic (pupil-dilating) powers have been examined by Sub-Assistant Surgeon Tarra Prosonno Roy (_Indian Med. Gaz._, Sept. 1870). He first applied a portion of a watery extract of the leaves of D. alba around the eyes; the pupils became widely dilated, and continued so for two days. He next tried an alcoholic extract of the seeds of the same species prepared by macerating half an ounce of the seeds in four ounces of country spirit, evaporating the tincture to dryness on a water bath, and dissolving the residue in one ounce of water. Experiments made with this solution prove beyond a doubt its power of causing dilatation of the pupil when locally applied; the strength of this watery solution being, at a rough estimate about equal in power to a four-grain (to the ounce) solution of Atropine.