Tea has refreshing and invigorating properties very comforting to one spent with toil. Its active principle is theine, a crystalline alkaloid found in both tea and coffee. Theine and caffeine were once supposed to be different substances, but have recently been found to be identical.

Tea is a valuable article of diet, though not a direct nutrient. It is classed with the so-called "accessory" foods, and, although not itself nutritious, aids, by its good flavor and stimulating properties, the digestion of other things. It is a nerve tonic, and is quite valuable as a curative agent for headache and some forms of indigestion. The slight stimulation resulting from its use is unattended by any after ill effects.

It is good for soldiers, hard-working people, travelers, and others who are much exposed to the rigors of climate.1

1 George Kennan, in his accounts of his perilous journeyings through Siberia, bears ample testimony to the comforting effects of hot tea. Often when he and his companion were chilled through, and almost dead with cold and fatigue, after many hours' travel over the frozen snows, they were revived by draughts of hot tea provided at the stations.