35. COFFEE.--This is an important addition to diet, and if moderately used is beneficial to persons of adult age. As commonly employed, it consists of an infusion in boiling water of the roasted and ground berry. The water extracts certain flavoring and coloring matters, but that which gives it its peculiar stimulant qualities is the alkaloid _caffein_. With most persons its action is that of a gentle stimulant, without any injurious reaction. It produces a restful feeling after exhausting efforts of mind or {76} body; it tranquilizes, but does not disqualify for labor; and hence it is highly esteemed by persons of literary pursuits. [Sidenote: 36. Another property of coffee? Miners of Belgium? The Caravans? Among armies? Taken with meals?] 36. Another property of coffee is, that it diminishes the waste of the tissues, and consequently permits the performance of excessive labor upon an economical and inadequate diet. This has been tested among the miners of Belgium. Their allowance of solid food was below that found necessary in prisons and elsewhere; but, with the addition of about four pints of coffee daily, they were enabled to undergo severe labor without reducing their muscular strength. The caravans which traverse the deserts are supported by coffee during long journeys and lengthened privation of food. Among armies it is indispensable in supplementing their imperfect rations, and in relieving the sense of fatigue after great exposure and long marches. When taken with meals, coffee is also thought to promote digestion. [Sidenote: 37. Effects of tea-drinking? Peculiar principle? The tea beverage, how made? Black and green tea? Excessive use of tea or coffee?] 37. TEA.--The effects of tea-drinking are very similar to those of coffee, and are due to a peculiar principle called _thein_. This principle is probably the same as that found in coffee, _caffein_, since the chemical composition of both is precisely alike. Tea, as a beverage, is made from the dried leaves of the plant by the addition of hot water; if the tea is boiled, the oil which gives it its agreeable flavor is driven off with the steam. There are two kinds of tea--the black and the green: the latter is sometimes injurious, producing wakefulness and other nervous symptoms. The excessive use of either coffee or tea will cause wakefulness. [Sidenote: 38. Experiments made during Kane's expedition?] 38. During Dr. Kane's expedition in the Arctic regions, the effects of these articles were compared. "After {77} repeated trials, the men took most kindly to coffee in the morning and tea in the evening. The coffee seemed to continue its influence throughout the day, and they seemed to grow hungry less rapidly than after drinking tea, while tea soothed them after a day's hard labor, and the better enabled them to sleep. They both operated upon fatigued men like a charm, and their superiority over alcoholic stimulants was very decided."