468 MATERIA MEDICA 



may be used in fevers, either alone, or as a vehicle for nitre, or 

 other medicine. 



Various other decoctions are occasionally employed, and some- 

 times preferred, on account of their cheapness, to more efficacious, 

 but more expensive, medicines ; yet, it must be recollected, that 

 some vegetables, such as peppermint, penny-royal, &c., have 

 their useful properties dissipated by nuich boiling, and should 

 therefore be only simmered for a few minutes, or only infused, 

 as it is termed. (See Infusions.) It is a common practice 

 with cattle doctors to boil their drenches in ale, by which the 

 spirit of tlie ale, and sometimes the essential parts of the other 

 ino;redients are, in some degree, evaporated. 



DECOMPOSITION is the separation of bodies which are 

 combined by chemical affinity, and can only be effi^cted by the 

 agency of some substance or substances which have a stronger 

 athnity for one or more of the constituents of the compound than 

 these have for each other. 



DELIQUESCENCE. When any solid possesses so great 

 an attraction for water as to absorb from the atmosphere a 

 quantity sufficient to dissolve it, it is said to deliquesce. Those, 

 again, that part with their water of crystallization vmtil they 

 become dry and fall into powder, are said to ejfloresce. 



DEMULCENTS. Medicines which have the power of di- 

 minishing the effect of acrimonious or stimulatinsi; substances 

 upon the sensible parts of the body. There are two sorts of 

 demulcents : the one, possessing an oily or mucilaginous quality, 

 sheathes the sensible part, and thereby defends it from the ac- 

 tion of the stimulus ; the other, being a wateiy fluid, dilutes the 

 stimulus, and diminishes, in a certain degree, its power. They 

 are supposed to act, when taken internally, not only by a direct 

 application to the stomach and bowels, but also by being ab- 

 sorbed into the circulation, and through that medium on the 

 lungs, kidneys, and bladder. Among the former may be 

 reckoned gum arable, gum tragacanth, and marsh- mallow, with 

 vai'ious oils ; the latter consists principally of water. 



DETERGENTS. A term employed in surgery for those 

 applications which have the power of cleansing foul ulcers, and 

 inducing a disposition to heal. They consist of caustics or es- 

 charotics, diluted or mixed with Avater, unctuous substances, 

 essential oils, or absorbent powders. 



DETERGENT POWDERS. 



No. 1. Blue vitriol (sulphate of copper) 



finely powdered 1 oz. 



Bole armenic '2 drs. — Mix. 



