12. STIMULATING BEVERAGES are those which contain a drug that stimulates
the nervous and the circulatory system; that is, one that acts on the
nerves and the circulation in such a way as to make them active and
alert. Common examples of these beverages are coffee, tea, and cocoa or
chocolate. If the nerves are in need of rest, it is dangerous to
stimulate them with such beverages, for, as the nervous system
indirectly affects all the organs of the body, the effects of this
stimulation are far-reaching. The immediate effect of the stimulant in
these beverages is to keep the drinker awake, thus causing
sleeplessness, or temporary insomnia. If tea and coffee are used
habitually and excessively, headaches, dull brains, and many nervous
troubles are liable to result.
13. The stimulant that is found in the leaves of tea is known as
_theine_; that found in coffee beans, _caffeine_; and that found in
cacao beans, from which cocoa and chocolate are made, _theobromine_.
Each of these stimulants is extracted by the hot liquid that is always
used to make the beverage. It is taken up by the liquid so quickly that
the method used to prepare the beverage makes little difference as to
the amount obtained. In other words, tea made by pouring water through
the leaves will contain nearly as much of the stimulant as tea made by
boiling the leaves.
14. In addition to the stimulant, tea and coffee contain _tannin_, or
_tannic acid_, an acid that is also obtained from the bark of certain
trees and used in the tanning of animal hides in the preparation of
leather. Tannin is not taken so quickly from tea and coffee by the hot
liquid used in preparing the beverage as is the stimulant, so that the
longer tea leaves and coffee grounds remain in the liquid, the more
tannic acid will be drawn out. This fact can be detected by the bitter
flavor and the puckery feeling in the mouth after drinking tea that has
been allowed to remain on the leaves or coffee that has stood for some
time on the grounds. Tannic acid has a decidedly bad effect on the
digestion in the stomach, so that if improperly prepared tea or coffee
is indulged in habitually, it may cause stomach disorders.