Source

The tea of commerce is prepared from the leaves of a shrub cultivated for this purpose in China, Japan, India, Ceylon, and other portions of Southern and Eastern Asia.

Classes Of Tea

There are two great classes of tea, the green and the black. The difference lies in the mode of preparation. Green teas are quickly dried and fired; black teas are allowed' to ferment a few hours before drying and firing.

Active Principles Of Tea

Tea has practically no food value. Its principal constituents are caffein, tannic acid, and a volatile oil.

Its flavor is due to the volatile oil; its stimulating properties to the caffein. Tannic acid is a soluble, bitter substance, which has a retarding effect on digestion.

When tea leaves are placed in boiling water, caffein is extracted very rapidly. Tannic acid is less soluble, and therefore it is possible to make tea with little of this principle by letting the water stand on the leaves only a short time. In practice, the hot, but not boiling water, should stand on the tea from 3 to 5 minutes. The water should be soft, as lime in hard water tends to make tannin dissolve more freely. Green or mixed tea is more powerful than black tea.

Effects Of Tea

Tea is mildly stimulating and hence refreshing, as it removes the sense of bodily fatigue. But the tannic acid retards the digestive action of the saliva and gastric juice, and tends to produce constipation. Tea is therefore not suitable for persons suffering from gastric disorders. The caffein is over-stimulating to the nervous system of many persons, causing restlessness, sleeplessness and muscular tremors. It should not be given to children, nor to adults with a tendency to nervousness. If you wish to avoid the retarding effect of tea on salivary digestion, direct the patient not to sip the beverage with the meal, but to eat first and drink afterward; in this way time is given for the saliva to perform its intended functions.

Tea is less likely to cause sleeplessness if lemon juice is substituted for milk.