478 PROTECTIVES 



pulsion of feces. According to the observations of Hertz, glycerin is 

 an irritant to the anal canal but not to the rectum. Glycerin is 

 slightly antiseptic probably through osmotic action. It is very use- 

 ful as a solvent for many drugs and as a vehicle for their external 

 application and internal administration. 



DEMULCENTS 



Demulcents are mucilaginous substances used to sooth and pro- 

 tect mucous membranes. They do this by forming a protective cov' 

 ering over them and thus prevent irritation from the secretions or 

 foreign matter. They are used 1. As a basis for cough remedies, 

 in which case they are soothing and protectant to the pharyngeal 

 mucous membrane. 2. In the treatment of poisoning. They act 

 by coating over the gastrointestinal mucous membrane and at the 

 same time prevent the absorption of most agents. 3. They are added 

 1o solutions of irritant drugs to prevent irritation of the stomach. 

 The most important are: 



ACACIA 



Synonym. Gum Arabic 



Acacia is the dried gummy exudation from a tree Acacia Senegal 

 and other African species of acacia. Insoluble in alcohol, slowly 

 but almost completely soluble in twice its weight of water forming a 

 mucilaginous liquid. 



Preparations. Mucilago Acacice — Mucilage of acacia. 



Pulvis Cretoe Compositus. Compound chalk powder. 



Uses. Acacia is used as a demulcent and excipient to hold emul- 

 sions, mixtures, etc. 



TRAGACANTHA — TRAGACANTH 



Tragacanth is the spontaneously dried gummy exudation from the 

 stems of Astragalus gummifer or other species of astragalus. 



Tragacanth is used similarly to acacia. On account of its in- 

 solubility it is used to hold heavy oils and powders in suspension. 



LINUM — LINSEED 



Linseed is the seed of the common flax. When unground it 

 forms a mucilage with water. When ground and mixed with two 

 or three times its weight of boiling water it forms a fairly firm mass 

 which is used as a poultice (flax seed poultice). 



