Pass beyond the point of moderation, and it becomes an irritant, precisely in the same way that an overdose of morphine will, instead of putting to sleep, for just so much longer time prevent any sleep at all.  The woman who can not eat, and who braces her nerves with a cup of green tea,—­the most powerful form of the herb,—­is doing a deeper wrong than she may be able to believe.  The immediate effect is delightful.  Lightness, exhilaration, and sense of energy are all there; but the re-action comes surely, and only a stronger dose next time accomplishes the end desired.  Nervous headaches, hysteria in its thousand forms, palpitations, and the long train of nervous symptoms, own inordinate tea and coffee drinking as their parent.  Taken in reasonable amounts, tea can not be said to be hurtful; and the medium qualities, carefully prepared, often make a more wholesome tea than that of the highest price, the harmful properties being strongest in the best.  If the water is soft, it should be used as soon as boiled, boiling causing all the gases which give flavor to water to escape.  In hard water, boiling softens it.  In all cases the water must be fresh, and poured boiling upon the proper portion of tea,—­the teapot having first been well scalded with boiling water.  Never boil any tea but English-breakfast tea; for all others, simple steeping gives the drink in perfection.

A disregard of these rules gives one the rank, black, unpleasant infusion too often offered as tea; while, if boiled in tin, it becomes a species of slow poison,—­the tannic acid in the tea acting upon the metal, and producing a chemical compound whose character it is hard to determine.  Various other plants possess the essential principle of tea, and are used as such; as in Paraguay, where the Brazilian holly is dried, and makes a tea very exhilarating in quality, but much more astringent.

The use of Coffee dates back even farther than that of tea.  Of the many varieties, Mocha and Java are finest in flavor, and a mixture of one-third Mocha with two-thirds Java gives the drink at its best.  As in tea, there are three chief constituents:  (1) A volatile oil, giving the aroma it possesses, but less in amount than that in tea. (2) Astringent matter,—­a modification of tannin, but also less than in tea. (3) Caffeine, now found identical with theine, but varying in amount in different varieties of coffee,—­being in some three or four per cent, in others less.

The most valuable property of coffee is its power of relieving the sensation of hunger and fatigue.  To the soldier on active service, nothing can take its place; and in our own army it became the custom often, not only to drink the infusion, but, if on a hard march, to eat the grounds also.  In all cases it diminishes the waste of tissue.  In hot weather it is too heating and stimulating, acting powerfully upon the liver, and, by producing over-activity of that organ, bringing about a general disturbance.