34 CAMELLIA THEA 



of tea vary very much in colour, odour, flavour, strength, and shape 

 caused by the degree in which their constituent leaves have been 

 rolled, and in other particulars. These differences arise, more 

 especially as we have seen, from their different modes of prepara- 

 tion, and hence they may be all arranged under the two heads of 

 Green and Black teas. The colour, odour, and taste of both green 

 and black teas are communicated to hot water, an infusion of the 

 former having a more or less greenish-yellow colour, a peculiar, 

 somewhat aromatic odour, and an astringent, feebly pungent, and 

 agreeably bitter taste ; while an infusion of the latter has a dark 

 brown colour, a somewhat similar but generally less agreeable 

 odour, and an astringent, bitterish, but less pungent taste. The 

 odour, taste, &c., of the different varieties of tea vary, however, 

 excessively, and are too well known to require further notice 

 here. 



The properties of tea depend essentially on the presence of 

 a volatile oil, tannic acid, and the alkaloid thein. This alka- 

 loid is also alluded to under Paullinia sorbilis, where it is said 

 to be identical with caffein, the alkaloid of coffee, and to be con- 

 tained in five different substances, namely, tea, coffee, guarana, 

 Paraguay tea, and Kola-nuts. Cocoa seeds also contain an alkaloid, 

 as is noticed under Theobroma Cacao, called theobromin, which 

 closely resembles thein both in its chemical characters and effects. 

 The amount of volatile oil varies in different teas from about 0'6 

 to O79 per cent. ; that of tannic acid from 13 to 18 per cent.; 

 and of thein, from 2 to 4 per cent. Tea also contains about 6 per 

 cent, of gluten. 



Properties and Uses. The principal use of tea is to form an 

 agreeable, slightly stimulating, soothing, and refreshing beverage. 

 It was also formerly believed that tea from the thein it contained, 

 had the effect of diminishing the waste of the body, and as any 

 substance that does this necessarily saves food, it was regarded as 

 indirectly nutritive ; but Dr. Edward Smith has shown that, on 

 the contrary, tea increases the bodily waste by acting as a 

 respiratory excitant, and in other ways. From containing 

 gluten, tea has also been regarded as directly nutritive, but in the 



