CHAPTEE XII 

 VOLATILE OIL GROUP 



ESSENTIAL OILS 



This group contains a large number of essential oils which are 

 obtained from plants by distillation, or more rarely by expression, 

 and should be distinguished from the Fixed or Fatty oils, which are 

 non-volatile. The volatile oils are found very largely in the fruits, 

 leaves, flowering parts and seeds of plants and are widely scattered 

 throiighout the vegetable kingdom. These oils are all extremely 

 odorous and are therefore used to overcome nauseous odors and' 

 tastes of medicine, for flavors and in toilet preparations. (They 

 are mainly objectionable to animals.) 



The composition of volatile oils is extremely variable. The 

 most common constituents are terpenes and some contain only these, 

 while in a few no terpene has been found. Terpenes may be briefly 

 defined as hydrocarbons of the aromatic series possessing the general 

 formula (C5Hfi)n. 



Characteristics. Volatile oils are generally clear, colorless 

 fluids, although a few of them may be green from the presence of 

 small quantities of vegetable coloring matter, while others are blue 

 from the presence of a terpene derivative (azulene). Upon long 

 standing they may acquire a yellowish color and an acid reaction from 

 the formation of resins. Most of these oils are light fluids but those 

 of copaiba and cubebs are more viscid. They are freely soluble in 

 alcohol, ether, chloroform and the fixed oils but only slightly soluble 

 in water. Many plants from which these oils are derived also con- 

 tain other principles, as bitters, but as many of the preparations used 

 in therapeutics are formed from the crude drug and not the oil, it 

 must be remembered that the oil may not be the only active prin- 

 ciple of a plant. 



Although they differ quite widely in chemical composition, their 

 actions are sufiiciently common to be discussed as a group. 



External and Local Action. All volatile oils possess antisep- 

 tic properties which are probably due in part to their volatility which 

 enables them to penetrate into the protoplasm of the cells and lessen 

 its vitality. They are also closely related to the benzene or benzol 

 series, all of which are antiseptics and protoplasmic poisons. They 

 differ greatly in their germicidal properties and are more toxic to the 



molds than to bacteria. 



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