VS4' , MATERIA MEDICA. 



bark, yet, when that cannot be procured, it 

 may be found an useful substitute. The dose 

 is about two ounces. 



OILS. Oils arc either JiJ^ed or volatile. 

 The former are procured from various ani- 

 mal and vegetable substances, generally by 

 means of pressure, from which circumstance 

 they have been named also expressed oils; 

 and are termed fixed, because they do not 

 evaporate, except at a vei^y high tempera- 

 ture, when they are decomposed. Volatile 

 oils, on the contrary, evaporate very rea- 

 dily, and are generally obtained from vege- 

 tables, by distillation, and as they commonly 

 contain all the essential qualities of the sub- 

 stance they are procured from, they have 

 been named also, Essential oils. 



The numerous ofncinal oils, directed in 

 the old dispensatories, are still highly es- 

 teemed by farriers, among which are, oil of 

 swallows, earthworms, johnswort, spike, 

 petre, &c. and we frequently meet with re- 

 ceipts for " strain or bruise oils," in which 

 more than a dozen diUerent kinds of oils are 

 ordered 1 Perhaps it may be an acceptable 

 piece of information to those who place 

 any confidence in these oils, that only three 



