Thein, the active principle in tea, is chemically identical with caffein in coffee.
Coffee
Coffee is prepared from the seeds of the coffee tree. The best known brands come from the Island of Java, Mocha, Rio de Janeiro, and Mexico.
Coffee, like tea, is not a food, it is a stimulant.
The active principle is caffein. This is an alkaloid and is a strong stimulant to the central nervous system. It quickens the heart action, and the stimulating effect is so apparent with many, that they cannot sleep for several hours after drinking it. Others drink coffee to quicken mental activity and to keep them awake.
It must be borne in mind, however, that there is a reactionary effect from all stimulants, and while coffee is not intoxicating, as alcohol, it has a similar effect on the nerves and heart.
Coffee has the redeeming feature of having a pleasing aroma, which, because of the effect on the mind, may incite the flow of gastric juice. Despite the fact that no morning beverage has quite the same pleasing aroma, or pungency, ordinarily one is much better without it.
Coffee stimulates the action of the heart and for this reason it is used in collapse to restore heart action.
It removes the sense of fatigue and is thus beneficial in some cases, as in the army, when long marches are necessary.