This section is from the book "Meals Medicinal", by W. T. Fernie. Also available from Amazon: Meals Medicinal: With "Herbal Simples" Curative Foods From the Cook in Place of Drugs From the Chemist.
The dietetic uses, and effects of Tea are fully discussed, and described in our Kitchen Physic, so that only a resume of the statements, and particulars there expounded, will be now adduced as relevant to its medicinal utility. The chemical composition of the leaf consists of theine (a crystallizable salt), tannin, casein, gum, sugar, starch, fat, aromatic oil, vegetable fibre, mineral substances, and water. When taken in an infusion of boiling water, Tea has been long noted as one of the very best, and most reliable nervine restoratives. The theine and aromatic oil not only act as sedatives to the nervous system in general, but they also exert a conservative effect on the different bodily structures, checking any disposition to a wasteful change therein of too rapid a nature, and to undue physical exhaustion. Tea contains potash, peroxide of iron, soda, and some other salts which are of essential importance to the human economy. "We have, therefore," says Liebig, "in Tea a beverage which comprises the active constituents of the most powerful mineral springs".
(Theodore Hook playfully styled his effervescing Mineral Waters "ftzzick") When milk, and sugar are added to the infusion, it becomes a useful, and nutritious food; whilst an important physical effect is brought about on the skin, and mucous membranes. The production of active perspiration by drinking hot Tea is a familiar fact; and the relief to the oppressive sense of heat in summer weather by doing the same thing is well known; an increase is caused in the sensible, and insensible perspiration, rendering much of the heat near the skin surface latent by free evaporation, and thus powerfully cooling the skin. Tea depends for its main quality on the alkaloid theine which it furnishes, and for its fragrance, on the volatile oils in the leaves. There were two original varieties of the plant, - Thea Chinensis, and Thea Assamica; the latter is found to retard conversion of the food-starches into dextrin and sugar by the saliva, more powerfully than a good China Tea. The extended use in this country of Tea, Coffee, and Cocoa within the last two centuries has led to results (says Sir Wm. Roberts) which evidence manifestly proves are not injurious.
A continued national progress, together with an increasing ascendency, serve to show that the addition of so important and peculiar a nutriment to our dietary, has improved our type of intellect by bettering the pabulum of the brain, and nervous system; indeed, it seems quite feasible to trace therefrom an upward, and onward change in the mental calibre, especially of the working classes, within the last three generations. There is to be observed an increased precision in mental operations, which has led to an improved criticism; also a rise, and progress of the exact sciences, and of the dependent industrial arts, more so perhaps within this brief epoch than in all the preceding ages of the world; whereas during the same epoch art and literature, which depend more upon the imagination, have practically stood still; the coincidence is at least suggestive!" Southey tells the story of his friend's great grandmother who made one of the party sitting down to the first portion of Tea that ever came to Penrith. "They boiled it in a kettle, and ate the leaves, with butter, and salt, wondering wherein the attraction lay".
Much has been asserted about the injurious effects on gastric digestion of the tannin contained so abundantly in many Teas. It has been alleged that meat-fibre is hardened by Tea, and that, pari passu, the coats of the stomach are liable to be similarly impaired; but such views are entirely theoretical. Leather is, no doubt, a very tough, indigestible substance; but meat-fibre is not gelatin like that which becomes tanned, and the coats of the living stomach are not dead membrane. As a fact, meat-fibre does not harden in Tea; on the contrary, it swells up nearly as freely in acidulated Tea of medium strength as in simple acidulated water. If it be wished to minimize the inhibitory action of Tea on the digestion of starches, instead of directing that the Tea should be infused for only two or three minutes, the plan should be to make it weak, and use it sparingly; also to drink it, not with the meal, but after the meal has been eaten. "And another device towards the same end, especially for persons of feeble digestive powers," says Sir Wm. Roberts, "is to introduce into the tea-pot with the Tea a pinch of bicarbonate of soda, which will completely obviate the deterrent effect of Tea on starch digestion; the mitigating effects on Tea of bicarbonate of soda, and of the commercial alkaline table-waters on wines, are well worth bearing in mind.
Besides it is really a delusion to suppose that by infusing Tea for only a short time (two or three minutes) the passing of the tannin into the infusion can be avoided; you can no more have Tea without tannin than you can have wine without alcohol. This tannin, in the free state, is one of the most soluble substances known; if some hot water is poured on a little heap of tannin the substance instantly dissolves like so much pounded sugar." But Dr. R. Hutchison teaches somewhat differently about this matter. He says: "There is less tannic acid dissolved after an infusion of three minutes than after five, and less after five than after ten; but beyond that one does not find an increase, for by then practically the whole of the soluble matters have been extracted from the leaf. The theine is so soluble that it is practically all dissolved out of the leaf immediately infusion has begun".
In Oxfordshire a Company has been formed of late for making small tablets which shall chemically remove the tannin from Teas, particularly those of India, and Ceylon, (which furnish tannin largely, so that infusions thereof are exceptionally strong, and harmful.) It is said that one of these tablets, if dropped into the teapot, will effectually counteract the injurious astringent principle, and thus confer the pleasure of Tea-drinking without any penalty attached thereto. The tablet is a combination of gelatine with alkaline salts; and, as gelatine is the chemical reagent of tannin, which it at once detects, and neutralizes, the use of this tablet justifies faith in its efficacy for making the drinking of Tea possible, and safe, to all digestions. The late Sir Andrew Clarke, who was a noted dietist, in some clinical remarks to his class of students, told them, with reference to Tea, (which he styled "a blessed beverage"), that "when of Indian growth it produces in some persons a kind of nervous disturbance which is very painful to witness.