The leaves of Thea chinensis, Sims (Camellia theifera, Griffith; Camellia Thea, Link).
ILLUSTRATION: Bentley and Trimen, Med. Plants, 34.
Botanical Source.—The tea plant, Thea chinensis, is an evergreen shrub, when uncultivated, attaining as much as 30 feet in height, but seldom reaching more than 6 or 7 feet when under cultivation. There are several varieties of this plant, among them Thea viridis (green tea) and Thea bohea (black tea). The commercial terms, green and black tea, do not refer to this botanical distinction. The several botanical varieties were formerly regarded as distinct species.
Thea viridis has many alternate, bright-brown and smooth branches, which are green and downy when young. The leaves are alternate, bright deep-green, oval or oval-lanceolate, short-stalked, very convex, serrated, entire toward the base, and at the apex, which is acuminate and emarginate; shining on both sides, blistered when old, and slightly downy beneath. The flowers are small, white, axillary, and solitary, with a rather heavy odor. Corolla of 5 to 9 petals, unequal, the outer one being shorter. Calyx without bracts, 5-cleft; segments imbricated and equal. Stamens numerous, smooth, adhering to the very base of the petals; filaments white and awl-shaped; anthers rounded, reniform, and opening at the base. Ovary ovate and pubescent; style simple at the base and trifid above. Capsule spheroidal, 3-celled, and often, by abortion, 1 or 2-celled; cells opening at the apex, 1 or, rarely, 2-seeded. Seeds spheroidal, wingless (L.).
Thea bohea, very much like the preceding, but the leaves are flatter, smaller, darker green, with small serratures, and terminating gradually in a point, and not at all acuminate or emarginate (L.). Flowers axillary and several together.
History, Preparation, and Description.—The tea plant is a native of eastern Asia, and was brought to Europe during the second half of the seventeenth century. It is extensively cultivated in China and Japan, also in Assam, Java, Bengal, Ceylon, Sicily, Portugal, Brazil, Jamaica, etc. It may also be successfully cultivated in South Carolina (see Amer. Jour. Pharm., 1898, p. 251). China and Japan furnish the bulk of the tea of commerce. According to investigations by Robert Fortune (1852) and other travelers, it appears that all the teas are collected from the same species, but their quality is subject to climatic influences, and dependent also on the soil, culture, and preparation. The tender tops of the shrub yield the finest teas, while the lower leaves yield the common kinds. The first crop also yields finer teas than subsequent crops, which are successively of poorer quality to the fifth or sixth crop. The accompanying illustration (Fig. 243), from Col. Money's Tea Cultivation (abstracted in Food and Food Adulterants, by Wiley, Spencer, and Ewell, Bulletin No. 13, United States Department of Agriculture, Part VII), shows a branch with leaves of different age, each representing a commercial grade of tea, as indicated. Distinction is made in commerce between green tea and black tea, the difference depending solely on the manner in which the leaves are treated in order to develop the aroma and taste of tea. Fresh tea leaves are non-aromatic, and have merely an astringent taste.
Green Teas are prepared by exposing the leaves to the sun's rays for 1 or 2 hours. In Japan they are treated with steam; subsequently they are roasted in iron pans over a charcoal fire; then they are rolled by hand on a bamboo table, and quickly dried in the roasting pan. This procedure "fixes" the green color of the tea. During the latter process, such additions as Prussian blue and gypsum are frequently made for the purpose of "improving" the green color (R. Fortune, The Tea Districts of China and India, 3d ed., Vol. II, 1853, p. 69, London). Commercial grades of green teas are Twankay, Young Hyson, Hyson-skin, Imperial, Gunpowder, etc.
BLACK TEAS are obtained by a process of fermentation. The leaves are allowed to lie on bamboo trays for about 12 hours, during which time they wither; then they are agitated by hand, and again allowed to lie in heaps for an hour or longer. Finally the leaves are alternately heated in pans and rolled on tables, this being repeated several times. After the last drying, the tea is sorted by means of sieves, and divided chiefly into three classes, depending on the size of the leaves—namely, Pekoe (the leaf buds), Souchong, and Bohea (see illustration, p. 1928 (Fig. 243)). Other commercial grades of black tea are Congou, Caper, and Oolong, etc. The rolling of the leaves is now frequently done by machinery, especially in Ceylon. This practice is preferable to the old method of performing the rolling with the hands, or even with the feet, as witnessed, for example, by Prof. Tichomirow (see below). It has been customary in tea-growing districts to improve the flavor of inferior teas by mixing them temporarily with certain fragrant flowers, such as of Jasminum Sambac, Aiton; Aglaia odorata, Loureiro; Gardenia pictorum, Hasskarl, etc., and afterward separating them out again. This statement, however, is discredited by Prof. Tichomirow, though he has seen special and high-grade green teas encased in boxes containing a layer of the flowers of Aglaia odorata. The leaves of the green tea have a dark bluish-green color, a pleasant, somewhat fragrant odor, and a bitterish, slightly astringent, herbaceous taste. They impart their peculiar taste and odor to boiling water by infusion, forming an agreeable and invigorating drink. The leaves of black tea are much darker-colored than those of the green, and their taste and odor is not so pleasant. They form a brownish infusion with boiling water. In Ceylon, black tea alone is manufactured, while in Japan only green tea can be produced, because the Japanese variety of tea does not bear fermentation (Flückiger, Pharmacognosie, 1891).
BRICK TEA.—A tablet tea is manufactured at Hankow, China, from common tea-dust, by steaming it and pressing it into wooden molds. A smaller and high-grade tablet is made from fine tea-dust by pressing it (dry) into steel molds by means of machinery. These grades are consumed throughout Russian Siberia. Brick tea is made from leaves and stalks of the tea shrub, which are powdered, sifted, steamed, and pressed into bricks of the size of an ordinary brick. This tea is used in Chinese Mongolia and Thibet (Bull. Kew Gardens, 1890, p. 109). (For a most interesting and detailed account of the cultivation of tea in Ceylon and China, see Prof. W. A. Tichomirow, Pharm. Zeitschrift f. Russland, 1892, p. 209, etc.)
Chemical Composition and Tests.—The aroma of tea leaves is due to a small quantity of volatile oil (0.6 to 1 per cent, Mulder). Other important constituents are theine (caffeine), varying in commercial specimens from 1 to 5 per cent, usually from 1 to 2 ½ per cent; large quantities of tannic acid, identical with gallotannic acid, from 7 to 21 per cent; gallic acid, oxalic acid, and quercetin, albuminous and coloring matters, and ash (3 to 7 per cent), of which about one-half is soluble in water. Boheic acid (C14H20O12), a deliquescent, amorphous substance, soluble in alcohol and water, was observed in black tea by Rochleder (1848). It forms a precipitate with lead acetate. A. Kossel (1888) found, in tea extract, theophylline (C7H8N4O2+H2O), isomeric with theobromine (see Theobroma), and melting at 264° C. (497.2° F.), and the base adenine (C5H5N5).
The seeds of Assam tea, according to Boorsma, contain two saponin-like substances—assamic acid and assamin (Proc. Amer. Pharm. Assoc., 1892, p. 784). David Hooper found the seeds to contain 9 per cent of total saponin, and 22.9 per cent of fixed oil, yet the latter can not be obtained free from the poisonous saponin (Pharm. Jour. Trans., Vol. XXV, 1895, p. 605).
Black tea, according to analysis of Y. Kozai (United States Bulletin No. 13, loc. cit.), contains less tannic acid than green tea, prepared from the same lot of fresh loaves. It evidently decomposes during fermentation. The amount of theine is practically the same in both. Theine (C8H10N4O2+H2O) was discovered in tea by Oudry (1827), and found identical with caffeine, in 1838, by Mulder and C. Jobst. (For its characteristics, see Caffeina.)
The "strength" of tea is not necessarily proportionate to the amount of theine present. David Hooper (Jahresb. der Pharm., 1890, p. 181) determined the tannin in 65 specimens of India and Ceylon teas, and found them (dried) to vary from 10 to 21 per cent; the finest grades contained the most tannin. P. Dvorkovitch, however (Amer. Jour. Pharm., 1892, p. 48), concludes that the quality or strength of tea is determined by the proportion of theine to total tannin, including that which is altered in the fermentation process. In the finest teas, the proportion of theine is large. Of great practical value and, of course, much simpler than the chemical analysis, is the infusion test, as carried out by experienced tea brokers. It consists in merely allowing the sample to lie in contact with a definite quantity of boiling water (about 1 in 40) for 5 minutes, and judging the quality of the infusion by its taste and flavor. This procedure removes only 20 per cent of extractive matter, while, if the tea were completely exhausted, about 35 to 40 per cent would be yielded, including all the tannin, which would make the decoction unpalatable and harmful. Messrs. Paul and Cownley have shown (Amer. Jour. Pharm., 1887, p. 627, from Pharm. Jour. Trans.) that, in making tea, about one-half of the total theine is removed. In one instance the residue still contained 1.7 per cent of theine, while in another instance, where exhaustion was carried as far as practicable, as much as 0.13 per cent of theine remained in the "exhausted" tea leaves. D. Hooper (loc. cit.) found that 5 minutes' infusion with boiling water will remove about one-third of the total tannin. (For the determination of theine in tea, see Paul and Cownley, loc. cit.) Petit and Terrat believe that chloroform or diluted alcohol (60 to 80 per cent) completely and readily abstract theine from tea, provided the latter be previously moistened (Proc. Amer. Pharm. Assoc., 1896, p. 602; also see P. Dvorkovitch, loc. cit.).
Tea is much subject to adulteration. Certain substances are mixed with it in order to give it a better appearance (facing), e. g., Prussian blue, indigo, turmeric, gypsum, graphite, magnetic oxide of iron, etc. The improvement of the flavor has been mentioned. Catechu has been added to increase the astringency. Another practice is to substitute partially extracted tea leaves (see methods of detection, by A. Tichomirow, Amer. Jour. Pharm., 1893, p. 302). Leaves of other plants which come into consideration as possible adulterants, and which are figured in the above United States Government Report, are those of maté, Paraguay tea (Ilex Paraguayensis), camellia (C. japonica), hawthorn, box-elder, horse chestnut, sycamore, rose, plum, elm, ash, willow, beech, oak, Missouri or golden currant, birch, poplar, raspberry, and Jersey tea (Ceanothus Americanus), also Vaccinium Arctostaphylos (see Bull. Kew Gardens, 1895, p. 61; also see Related Products, below).
Action, Medical Uses, and Dosage.—Tea is a mild stimulant and astringent. Used in moderation, the infusion, when not too strong, is a harmless and refreshing beverage. As to its effects upon the constitution, there is quite a diversity of opinion, but it is very probable that, with healthy persons, no pernicious influences arise from its use, unless taken in large quantities, or very strong. When made into a weak infusion, it is very agreeable to the invalid, and may be used in fevers and inflammatory diseases, when it is desired to check sleep. In colds, catarrhs, and slight attacks of rheumatism, warm tea is taken as a diluent, diuretic, and diaphoretic. It frequently relieves headache, and allays the irritation of the stomach produced by intemperance of the previous day. With some persons, however, tea produces very unpleasant nervous symptoms, as tremors, anxiety, headache, sleeplessness, etc. Tea is said to be a sedative to the heart and blood vessels, and Liebig considers it to possess considerable nutritive power. Black tea is generally preferred by those of weak or delicate nerves, on account of its being less apt to produce disagreeable nervous symptoms. Externally, the infusion has been used with advantage as a collyrium. The essential oil of tea exerts a most powerfully stimulating and intoxicating effect. In China, tea is seldom used till it is a year old, on account of the well-known intoxicating effects of new tea, due probably to the larger proportion of essential oil contained in the freshly-dried leaf (W. A. Miller). According to Dr. Lewin, the effects of theine and caffeine are identical, with the exception that the first is a less powerful toxic than the latter, requiring double the doses to produce the same effect, and likewise occasions convulsive movements in the limbs, which have not been noticed from the action of the latter (Arch. de Phys., Norm., et Path., 1868).
Later investigators, however, consider theine and caffeine physiologically identical with each other, as well as with theobromine, cocaine, and guaranine. While their principles are thus identical, it is equally true that coffee and tea differ considerably in their effects and, of the two, the latter is more apt to harm the nervous system. Both tea and coffee induce wakefulness, but that of the former may partake of the character of a distressing insomnia, while the latter induces a pleasant, dreamy wakefulness. Both, however, in proper amounts, produce a feeling of mild exhilaration and well-being. Immoderate quantities of tea long-continued, may give rise to dyspepsia, constipation, headache, nervous unrest, hysteria, cardiac palpitation, and other irregularities, tremors, neuralgia, difficult breathing, ringing in the ears, physical and mental exhaustion, and other deleterious effects. The infusion of tea may be used freely; the fluid extract in doses of ½ to 1 fluid drachm, well diluted with water.
Related Products.—LIE TEA. "This substance, as its name implies, is an imitation of tea, usually containing fragments or dust of the genuine leaves, foreign leaves, and mineral matters, held together by means of a starch solution, and colored by one of the facing preparations. It is stated that gunpowder and imperial teas are more subject to this form of adulteration. Of the samples of tea examined by the Department of Agriculture, all were free from lie tea. According to Hassall, the percentage of ash in lie tea ranges from 13.05 to 52.92 for black teas, and 13.13 to 56.34 for green teas. The same authority also found black teas containing from 6 to 17.7 per cent of lie tea, and green teas containing 1.38 to 48.46 per cent of this adulterant. To detect lie tea, treat the suspected sample with boiling water. If it contains this adulterant, portions will break up into dust and leaf fragments" (Food and Food Adulterants.—Wiley).
BUSH TEA (Honig thee).—South Africa. Species of Cyclopia, probably C. brachypoda and C. longifolia, are utilized by the inhabitants of Cape Colony as a substitute for tea (see Pharm. Jour. Trans., Vol. XI, 1881, pp. 549 and 569). H. G. Greenish showed that it contained cyclopin (C25H28O13), a glucosid, yielding sugar and cyclopia-red. No theine could be detected.
TEA OIL.—The Chinese use tea oil for lamps and as an article of food. It is pale-yellow, nearly odorless, of specific gravity 0.927, burns with a clear, white flame, is soluble in ether, but insoluble in alcohol and water. It is obtained, by warm pressure, from the seeds of various species of the genus Camellia, as the C. japonica, C. oleifera, Abel; Thea oleosa, Loureiro; or C. sasangua, Thunberg. The press-cake contains a poisonous, saponin-like substance (see Bull. Kew Gardens, 1888, p. 264).
Camellia drupifera, Loureiro, yields a similar oil.
Thea Japonica, Baillon (Thea Camellia, Hoffmann; Camellia Japonica, Linné).—This Japanese shrub, cultivated here for its ornamental beauty, yields poisonous seeds. Martin and Katsuyama (1878) obtained an acrid, semisolid, fixed oil, tannin, and a poisonous glucosid, camellin, somewhat soluble in hot water, little soluble in ether, easily soluble in alcohol.