228 CHEMICAL, MEDICAL AND DIETICAL PROPERTIES. 



infirmities of advancing age, especially when the digestive 

 powers become enfeebled and the size and weight of the 

 body begin perceptibly to diminish, the value of tea in 

 checking the rapid waste of tissue is particularly observa- 

 able, and persons, when very much fatigued, will be 

 sooner refreshed by drinking a cup of moderately strong, 

 good tea, than by drinking wine or spirits of any kind. 

 In allaying or satisfying severe thirst, no beverage will 

 be found as efficacious as a draught of cold tea. 



Lettson furnishes a calculation, partly his own and 

 partly from other sources, in which he endeavors to 

 prove how much is, in his view, unnecessarily expended 

 by the poor for tea. But the observations of Liebig, if 

 correct, and in all probability they are, offer a satisfactory 

 explanation of the cause of the partiality of the poorer 

 classes, not alone for tea, but for tea of an expensive and 

 therefore superior quality. " We shall never certainly," 

 he says, " be able to discover how people were led to the 

 use of hot infusions of the leaves of a certain shrub (tea) 

 or a decoction of certain roasted seeds (coffee); some 

 cause there must be which would explain how the 

 practice has become a necessary of life to whole nations." 

 But it is still more remarkable that the beneficial effects 

 of both plants on the health must be ascribed to one and 

 the same substance, the presence of which in two vege- 

 tables belonging to natural families, the product of different 

 quarters of the globe, could hardly have presented itself 

 to the boldest imagination, recent research having shown 

 in such a manner as to exclude all doubt that the 

 caffeine of coffee and the theine of tea are in all respects 

 identical. And without entering into the medical action 

 of this principle, it will surely appear a most startling 

 fact, even if we deny its influence on the process of 

 secretion, that this substance, with the addition of oxygen 



