FORMS OF MEDICINES. 



17 



divided into the requisite number of pills. Sometimes they are co- 

 vered with gelatine, to conceal their disagreeable taste. 



Powders. — Such medicines arc given in the form of powder as 

 are not very bulky, nor of very disagreeable taste, and have no cor- 

 rosive property. Deliquescent substances, and those containing 

 much fixed oil, are unfit to be used in powder ; as also such crystal- 

 line salts as contain water of crystallization, unless this be pre- 

 viously expelled by heat. The substance may be reduced to the 

 state of powder by means of a mortar and pestle, made either of 

 metal, glass, or wedgewood. The coarser particles are separated by 

 sieves made of various materials. Some require to be submitted to 

 the processes of levigation and elutriation. By the former of these 

 terms is meant the rubbing of the substance, previously moistened, 

 between two smooth pieces of hard flat stone ; the latter term signi- 

 fies the agitation of the matter in water, allowing the coarser parti- 

 cles to settle, pouring off the liquor for the finer ones to subside, and 

 lastly, decanting and drying the powder. 



The lighter powders may be administered suspended in water, or 

 any other convenient vehicle : the heavy insoluble ones, in syrup, 

 molasses, or honey. 



Troches. — Small solid masses, in which the medicinal substance is 

 incorporated with the sugar and gum,— intended to be held in the 

 mouth and allowed slowly to dissolve. They are used chiefly in 

 affections of the throat. 



Confections. — Soft solids, made by incorporating medical sub- 

 stances with sugar: they comprise also conserves. 



Electuaries. — Usually extemporaneous prescriptions, made by 

 mixing medicines (generally powders) with honey or molasses. 



2. Liquid forms. — These include decoctions^ infusions^ mixtures^ 

 tinctures., wines., syrnps^ vinegars., oxymds., and honeys. 



Decoctions. — Preparations in which the active properties of ve- 

 getables are extracted by boiling. The boiling should take place in 

 a covered vessel. Certain vegetables are unfit for decoction, as those 

 which possess a volatile oil, or such as contain much inert, starchy, 

 or mucilaginous matter. 



Infusions. — These differ from decoctions in not being boiled. 

 They may be made either with cold or boiling water. Cold water 

 is preferred where the active principle is volatile, or easily injured 

 by heat, or where it is desirable to avoid the solution of some prin- 

 ciple which is insoluble at a low temperature. Both infusions and 

 decoctions usually require to he, filtered ; this process may be per- 

 formed either by using unsized paper in a common funnel, or by 

 percolation or displacement. 



Mixtures. — These consist generally of one or more insoluble 

 substances, suspended in water by means of gum, sugar, or yelk of 

 egg. When an oil is suspended in this way, the mixture is called 



2* 



