444 VEGETABLE SUBSTANCES. 



CHAPTER XXVIIT. 

 GUM-RESINS. 



FRANKINCENSE OLIBANUM GAMBOGE CAMPHOR 



CAOUTCHOUC. 



IN tropical climates vegetation is so luxurant that 

 the juices of various trees are produced superabun- 

 dantly ; this exuberance of production is thrown off 

 from natural cracks in the bark, or from artificial 

 incisions, and concretes, by exposure to sun and air, 

 into irregular masses of various forms, which are 

 therefore the juices of the respective plants as nearly 

 as possible in their natural state. Some of these are 

 of a mixed nature, having the characteristic proper- 

 ties which would be produced by a combination of 

 gum and resin, and they are therefore called gum- 

 resins. To the gummy part they owe their solubility 

 in water ; and they partake of the qualities of resin in 

 being fusible, in igniting with much flame, and in 

 giving by distillation a large portion of volatile oil, 

 and some ammonia. 



Some of these gum-resins emit a most grateful 

 perfume on being burnt, and are used as incense on 

 the altars of the Catholic chapels. On the continent 

 of Europe the consumption of these aromatic ingre- 

 dients is very considerable. They have always been 

 much prized for this purpose, and from the earliest 

 records we find in the temples of the ancients the 

 wreathing smoke, rich in delicious odours, encircling 

 and rendering more acceptable the sacrifices offered 

 up to their gods ; while in the writings of some 

 moderns we find how much value was attached to 



