SECT. XVI. GUM-RESINS. 441 



Its specific gravity is 1-212. It is employed in the 

 composition of ointments and plasters. 



Ammoniac. This substance is brought from 

 Africa in the form of small tears ; but nothing cer- 

 tain is known concerning the plant which yields 

 it. It is thought to be a species of Ferula. The 

 colour of the substance is yellow, and the taste 

 nauseous. It is used in medicine. 



Scammony. This substance is the produce of 

 the Convolvulus Scammonia, a climbing plant which 

 grows in Persia. The root when cut yields a milky 

 juice by expression, which, when it concretes, forms 

 scammony. Its colour is dark grey, its smell 

 nauseous when rubbed, and its taste bitter. It 

 forms with water a green opaque liquid. It is 

 much employed in medicine, and operates as a 

 strong cathartic. 



Opoponax. The plant from which this substance 

 is obtained is the Pastinaca Opoponax, a native of 

 the countries of the Levant. It exudes in the 

 state of a milky juice from incisions made in the 

 root. It is afterwards dried in the sun, and is gene- 

 rally to be met with in lumps of a reddish colour, 

 and white within. Its taste is bitter and acrid, and 

 it forms with water ajnilky solution. 



Euphorbium. This substance is the produce of 

 the Euphorbia officinalis, a plant which grows in 

 Africa. It is the milky juice of the plant dried 

 in the sun, and obtained by means of incisions. 

 It assumes the form of small yellow tears. It has 



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