PREPARATIONS. 9 



magnesium and potassium. Arabin is soluble in 

 water; bassorin is not soluble, but swells into a 

 gelatinoid mass. Pectin, vegetable jelly, C^E^jO.^, 

 4EL,O, occurs in a few medicinal plants, and, like the 

 mucilage yielded by several others, is allied to gum. 

 Gum-resins are natural or artificial exudations from 

 plants, containing various proportions of gums and 

 resins, or more frequently of gums, resins, and volatile 

 oils. 



Alkaloids are - active principles formed within 

 plants, which resemble alkalies in turning red litmus- 

 paper blue, and form salts with acids. As a rule, 

 they are crystalline solids, rarely liquids; sparingly 

 soluble in water, but readily in alcohol, the solution 

 being intensely bitter. 



Organic acids of great variety exist in plants, 

 combined with the inorganic bases, such as potash and 

 lime, with alkaloids, or possibly free. 



Neutral substances are a very large and mixed 

 group, including the carbohydrates, such as starch, 

 sugars, gums, etc. ; albuminous bodies, which occa- 

 sionally act as ferments ; a few bitter principles ; and 



Glucosides are chiefly neutral bodies, capable of 

 being decomposed in the presence of water into 

 glucose and a second substance, different in each 

 instance. 



The remaining constituents of organic drugs do 

 not call for special notice. 



Dose. The Pharmacopoeia suggests the limits 

 within which the different substances and their pre- 

 parations may be safely given to an adult, 

 must be carefully learned. The principles of dosage 

 will be presently discussed. 



Preparations. The list of preparations made 

 from the drug, with the principal ingredients, strength, 

 and doses of each, will conclude the account of its 



