Chemists find in manufacturing tea leaves three principal
constituents to which all the physiological effects of tea are
attributed. These are, (1) Theine, (2) Essential or Volatile
Oils, (3) Tannin.

Theine is present in the green leaf of tea, and is apparently
unchanged in the manufactured leaf and in the infusion or
beverage. We regard it as the one essential and the most valuable
element of all teas, physiologically considered. Strangely enough
theine is the one important constituent which is entirely
neglected by the tea-tester and the trader. In testing and
grading teas for purchase and sale, their appearance, odor and
taste, their color and body when "drawn," determine their
pecuniary value, without relation to their percentage of theine,
or its effects upon the tester.

Theine has been found in nature in but a few plants, as in tea,
in coffee, (then termed caffein), in Mat'e (Paraguay or Brazilian
tea), and in the Kola nut of Africa. A very similar principle,
having analogous properties, but containing more nitrogen, exists
in cocoa, (theobroma).

Theine, when isolated by heat from the tea leaf or infusions,
condenses in minute white needles or crystals, having no odor and
but a faintly bitter taste. In manufactured tea leaves, theine
constitutes from one to five percent. of their weight. According
to Professor Johnston, three or four grains per day of this
substance may be taken without injury by most persons; or such
quantity as would be contained in half and ounce of Chinese black