, NATURE, AND SOURCES OF DRUGS. 5 



of the inorganic materia medica. It includes many 

 of the chemical elements, and a great variety of com- 

 pounds of the same. 



Vegetable drugs are derived from entire plants, 

 including fungi and lichens, stems (woods), green tops 

 and twigs, roots and rhizomes, barks and leaves, buds, 

 flowers, parts of flowers and flowering tops, fruits and 

 seeds ; and various vegetable products, including fixed 

 and volatile oils, resins, oleo-resins, balsams, gums, 

 gum-resins, inspissated juices and secretions. The 

 animal materia medica includes entire animals, portions 

 of animals, and products yielded either during life or 

 after death. 



The methods for obtaining the drugs will generally 

 be given, and must be learned by the student, who 

 should repeat for himself as many as possible of the 

 easier processes. Most of these are already familiar to 

 him in chemistry, such as solution, filtration, evapora- 

 tion, crystallisation, precipitation, decantation, subli- 

 mation, distillation, destructive distillation, digestion, 

 and washing. A few specially pharmaceutical pro- 

 cesses will, however, require to be defined : 



Pulverisation, the powdering of drugs, is done on 

 a large scale in powerful drug-mills. On a small scale 

 it may be done by simple trituration (triturare, to 

 pound), or powdering in the dry state ; by levigation 

 (levigare, to make smooth or fine), or rubbing down 

 with the aid of a little fluid, the resulting paste bcin^ 

 afterwards dried; or by mediate pulveriwt >'<>/>, in 

 which some very hard substance or medium is mixed 

 with the drug, in order to break up its sukstamv 

 thoroughly. Powdered drugs necessarily require 

 sifting. 



Elutriation (elutriare, from eluere, to wash out) 

 consists in diffusing an insoluble powder in water, 

 allowing only the heavier part to settle, and decanting 

 the fluid; allowing this again to settle for a longer 



