ACTION OF VOLATILE OILS 283 



When applied to the skin they produce irritation, itching and 

 redness followed by numbness or anesthesia, the irritant effect being 

 increased by their volatility. The oils of cloves and cinnamon are 

 used in dentistry to relieve pain and act as antiseptics. The redness 

 may be due to the penetration of the oil to the cutaneous arterioles or 

 veins, or to reflex action from the irritated terminations of the 

 sensory nerves acting on the vasomotor center. 



Digestive System. Volatile oils, in strong solution, are irri- 

 tant in the mouth. They have a hot burning taste, and if kept in 

 the mouth, cause redness and irritation of the mucous membranes, 

 although a few of them (peppermint) first have a cooling sensa- 

 tion. The sense of smell is at the same time affected by these oils, 

 which are nearly all characterized by distinctive odors. The irrita- 

 tion brings about a reflex secretion of saliva which may be very 

 profuse. 



In the stomach they exert the same effect as in the mouth 

 or upon the skin, that is, a mild form of irritation, leading to in- 

 creased vascularity, more rapid absorption, augmented movement; 

 at the same time they exert their powerful antiseptic action. These 

 actions cause a sense of warmth to the stomach and are often fol- 

 lowed by the expulsion of gas and the relief of colic. They are 

 therefore called carminatives. Similar effects are believed to be 

 produced in the intestines because the administration of these oils is 

 often followed by lessened flatulence and distention, and relief in 

 many cases of colic. 



Blood. The volatile oils when administered by the mouth pro- 

 duce a leiicocytosis especially of the polynuclear variety, but this 

 is observed in congestion of the stomach and intestines from other 

 causes, and does not follow the intravenous or subcutaneous injec- 

 tion of the volatile oils, so that it cannot be considered as a specific 

 action. 



Central Nervous System. The volatile oils do not affect the 

 central nervous system except in very large non-medicinal^ doses. 

 The action is one of stimulation, followed by depression, and is espe- 

 cially marked upon the brain. The effect is thought to be due to 

 the benzene nucleus of the terpenes and varies greatly with the dif- 

 ferent oils. Generally the stimulation is not a very marked feature; 

 in the case of turpentine it is very transitory and the narcotic ac- 

 tion is more pronounced. 



Absorption. They are rapidly absorbed. 



Excretion. The volatile oils are excreted by the kidneys, lungs 

 and skin. During their excretion by the lungs their odor may be 

 readily recognized in the breath and they exert a mild irritation 

 leading to stimulation of the ciliated epithelium and to reflex cough- 

 ing and are therefore used as expectorants. At one time it was 

 hoped that they would exert a sufiiciently strong antiseptic action 



