Prescriptions usually contain two or more of the following four representative constituents: (1) The _basis_ or active ingredients. The practice of conjoining several active medicines has wisely been abandoned. Occasionally, however, it may be advantageous to give together two medicines producing their effects in somewhat different ways. Thus, spasms of the bowels are more often effectually controlled by the conjunction of a stimulant like ether and an anodyne like opium than by either given alone. Pain which is not alleviated by either morphine or atropine is sometimes abated by giving them together. (2) The _adjuvant_ is introduced in order to increase, moderate or modify the action of the basis. Frequently its chief object is to insure solubility and ready absorption. (3) A _corrective_ is occasionally required to temper the effects of the basis. Thus a small dose of opium is prescribed with oil or other laxative in cases of diarrhoea; ginger is generally added to the aloetic mass to prevent its griping. (4) The _vehicle_ generally consists of some comparatively inert substance, added to facilitate administration, such as the treacle, linseed meal or licorice powder used as an excipient for boluses and pills, the benzoated lard or vaseline used for making ointments, and the water given in drenches. Example: ℞ Barb. Aloes ℥i. Calomel ʒi. Ginger ʒii. Molasses ℥ss. M. et fiat massa, in bolus 1. Sig. Give at once. --John Jones. In the above prescription aloes is the basis; calomel as an adjuvant, ginger as a corrective, molasses as an excipient. * * * * * A prescription is composed of several parts, which may be considered as follows: 1. Heading. 2. Names and quantities of drugs. 3. Directions to compounder. 4. Directions to attendant. 5. Signature of writer. 1. For Gray Tom. July 22, 1916. ℞ { Cupri sulph., 2. { Ferri. sulph. exsic., aa. ℥iss. { Pulv. belladonna fol., { Pulv. gentian rad. aa. ℥iii. 3. M. Ft. Chart No. XII. 4. Sig.--One powder three or four times daily in syrup. --John Jones. ABBREVIATIONS PRESCRIPTION WRITING. Words, phrases and abbreviations commonly used in prescription writing.