18 MATERIA MEDICA. 



an emulsion. A good deal of care and dexterity are requisite in 

 making a uniform mixture. 



Tinctures. — Solutions of medicated substances in alcohol, or di- 

 luted alcohol. They are usually macerated, at ordinary tempera- 

 tures, in well-stopped bottles, frequently agitating. Undiluted (offi- 

 cinal) alcohol is employed where the substance to be dissolved is 

 insoluble in water, — as resins, essential oils, &c.; but diluted alcohol 

 is preferred when the substance is soluble both in alcohol and water. 



Syrups. — Preparations in which the medical substance is pre- 

 served in a concentrated solution of sugar. SiTiiple syrup consists 

 of two and a-half pounds of white sugar dissolved in a pint of water. 

 Medicated syrups are made either by adding the proper amount of 

 sugar to vegetable infusions, decoctions, juices, &c., or by adding 

 the tincture of the substance to simple syrup, and afterwards driving 

 off the alcohol by the heat of a sand bath. 



Honeys. — These are analogous to syrups, the difference being 

 that honey is employed to preserve the medical substance, instead of 

 a solution of sugar. They are said to be less apt to become candied. 



Oxyjuels are preparations in which honey and vinegar are com- 

 bined. 



Vinegars. — Liquids in which distilled vinegar is employed as the 

 solvent. 



Besides the above forms of medicines, which are employed for 

 internal administration, there are several others which are used ex- 

 clusively as external applications ; these are liniments^ oint7nents, 

 cerates^ pdasters^ and cataplasms. 



Liniments. — Oily compounds intended to be applied to the sur- 

 face by bathing, or by saturating cloths with them. 



Ointments. — Soft solids which melt at the temperature of the 

 body. 



Cerates are rather harder than ointments : they do not melt at 

 the temperature of the body. Simjjle cerate consists of fresh lard 

 and while wax. 



Plasters. — These are solid at ordinary temperatures, and require 

 to be heated before they can be spread. They are usually kept in 

 rolls, and when wanted for use are spread upon sheepskin, linen, 

 muslin, or even paper ; a small margin being left at the edges un- 

 covered. 



Cataplasms ov poultices. — These are soft moist preparations, in- 

 tended to relax and soften the parts to which they are applied. 

 They are usually made from bread and milk, flaxseed meal, <fec. 



The iveights and measures recognised by the pharmacopoeia in the 

 compounding and dispensing of medicines are the Apothecaries'* 

 vjeiidit., and the Apothecaries' or tvhie measure^ though medicines 

 are purchased and sold by the wholesale dealer by the Avoirdupois 

 weight. The imperial pint of the British pharmacopoeia (not re- 



