8 MATERIA MEDIC A AND THERAPEUTICS. 



the other hand, the organic drugs are frequently 

 highly complex, the chief proximate principles being 

 the following : Fixed oils, volatile oils, resins, oleo- 

 resins, gums, gum-resins, balsams, pectin, alkaloids, 

 acids, neutral substances, glucosides, starch, sugar, 

 cellulose, albuminous substances, ferments, colouring 

 matter, salts, and extractives. Some of these demand 

 general consideration. 



Fixed oils are extracted by expression (if possible, 

 without the aid of heat) from the seeds or fruits of 

 plants, or from animal tissues. They are composed of 

 oleate, with palmitate and stearate of glyceryl ; that 

 is, are compounds of fatty acids (oleic, palmitic, and 

 stearic, as well as of other, less common) with the 

 radical glyceryl, C 3 H 5 . With caustic alkalies or 

 metallic oxides, they form soaps, the metal displacing 

 the glyceryl, which is hydrated, and becomes glycerine, 

 C 3 H 5 3HO. 



Volatile Oils; JZesins ; Oleo-resins ; Balsams. 

 Volatile oils are obtained by distillation from entire 

 plants, flowers, fruits, or seeds. Most of them are 

 colourless when pure, and highly aromatic. They 

 consist of a liquid hydrocarbon or elceopten, generally 

 isomeric or identical with terpene, the hydrocarbon of 

 oil of turpentine, C 10 H ]6 ; and of an oxydised hydro- 

 carbon, usually a solid body, or stearopten, like 

 camphor, C 10 H 16 O. A few volatile oils contain sul- 

 phur and nitrogen. Further oxydation converts a 

 portion of volatile oils into resins, solid, brittle, non- 

 volatile bodies, and thus gives rise to oleo-resins, 

 which can be broken up into their two constituents 

 i by distillation. Resins or oleo-resins yielding benzoic 

 lor cinnamic acids are called balsams. 



Gums are exudations from the stems of plants. 

 They consist of two rather complex carbohydrates, 

 arabin, C I2 H 2 ,O n , and bassorin, C^H^On,, which play 

 the part of acid radicals, and exist in gums as salts of 



