A treatise on foreign teas / Abstracted from an ingenious work, lately published, entitled An essay on the nerves

by Hugh Smith

ESSAY ON TEAS.

There is, perhaps, no subject on which there has been more declamation, for and against its properties and effects, than those of teas imported into this country by the companies trading from the different maritime nations of Europe to China and India. Nor has there been a controversy in which the health of the community has been so materially concerned, that has afforded so little direction of moment to those who would wish to ascertain the truth of such teas being either beneficial, injurious, or innocent in their effects. Amidst a mass of declamatory assertion so little intelligence is to be gained, that those who have had the greatest interest in being informed of the real qualities of teas, have most abandoned the enquiry before they obtained the least knowledge of what they sought. Either perplexed with abstruse science, or dissatisfied with assertion equally unfounded and unsupported, thousands have discontinued the research, and committed themselves to fatal experience. Thus have too many acquired a knowledge of the detrimental qualities of teas, by the ruin of their constitution. To avoid therefore such an inconvenience, the greatest care will be taken to prevent an indiscriminate reference to authors, whose sentiments can neither sanction adduced arguments or illustrate technical allusions. The enquiry will be made with some reference to science, but more to convince by demonstration than to confound by abstruse perplexities. So that, while empty declamation is avoided, the principles of truth are meant to be investigated by reason and experience. With this view, the Nature of Green, Souchong, and Bohea teas is first considered. To judge of the nature of these herbs with equal candour and propriety, it may be necessary to consider their qualities in relation to what are ascribed them, and what have been discovered by their analysis, and what have resulted from experience. The virtues that have been ascribed to them are chiefly, being a greatful diluent in health, and salutary in sickness, by attenuating viscid juices, promoting natural excretions, exciting appetite, and proving particularly serviceable in fevers, immoderate sleepiness, and head-aches after a debauch. It is also added to the list of their ascribed virtues, that there is no plant yet known, the infusions of which pass more freely from the body, or more speedily excite the spirits. To a person of any physical knowledge, these qualities will either appear contradictory in themselves, or rather ultimately injurious, than absolutely beneficial. As the full examination of these assumed qualities, by the rules of science, would require a volume, instead of a few pages, which the limits of this Essay will afford, the enquiry must be made as perspicuous as the necessity of brevity will admit. Allowing they are diluting in health, their constant use may so attenuate the liquids as to destroy their natural force and tensity. But Boerhaave says, there is no proper diluent but water; it is therefore evident it is the water, and not the tea, which is the diluting medium. With respect to its being an attenuative of viscid humours, it can never possess this virtue from being a diluent, for an attenuant acts specially on the particles, by diminishing their bulk, while the diluent acts upon the whole mass of the fluid.

The general body of the liquid may be diluted while the viscid humours remain unresolved. Indeed, the operation of an attenuant is not easily known; for many are surprised that a slight inflammation should be so difficult to dissipate. But their surprise would cease, were they to consider, that medicines act more generally upon the whole body than abstractedly upon the part affected. Suppose to attenuate some coagulated blood, six grains of volatile salt were given, how small a proportion must come to the part diseased, when these grains, by the laws of circulation, will mix with the entire mass of blood, consisting at least of thirty pounds!

Teas being said to promote natural excretions, can be no recommendation of what is generally used; for this constant effect must render them too copious, and thus, according to all physical experience, the blood must be thickened in the greater vessels, which frequently terminates in an atrophy.

The appetite being excited by the drinking of tea, is more a proof of its attrition of the solids than any stimulus to a wholesome desire of food. This quality accounts for the acrimonious effects too many have experienced by its use. Many have not only had their blood impoverished, but corrupted by the constant drinking of these teas. Whether it arises from any positive acrimonious salt it naturally possesses, or from any acquired corrosiveness from its mode of drying, is not here necessary to enquire: it is only requisite to state that a pernicious effect is too fatally experienced by those who are unfortunately its slaves.

How India tea can be serviceable in fevers is not easy to be understood; for, if it has that effect upon the nerves to excite watchfulness, it must greatly tend to increase, instead of diminish feverish symptoms. Dr. Buchan attributes even one cause of the palsy to drinking much tea or coffee, &c. and, in a note, he subjoins: "Many people imagine that tea has no tendency to hurt the nerves, and that drinking the same quantity of warm water would be equally pernicious. This, however, seems to be a mistake, many persons drinking three or four cups of warm milk and water daily, without feeling any bad consequences; yet the same quantity of tea will make their hands shake for twenty-four hours. That tea affects the nerves is likewise evident from its preventing sleep, occasioning giddiness, dimness of the sight, sickness, &c."

With regard to India teas possessing the quality of exciting the spirits, this, like every other stimulus, either by constant use loses its effect, or unnerves the system it is meant to strengthen. The nerves through which the animal spirits circulate being, like the strings of a violin or harpsichord, too frequently braced, lose, at last, their natural tensity, and thus render the human frame one system of debility.

Having thus, as briefly as possible, stated that even their ascribed virtues are either derogatory to all physical principle, or else destructive to the constitution, from their constant use, the nature of India teas is next considered, with respect to what appears to be their chief component parts, from analyzation.

Teas have been found to consist principally of narcotic salts, some astringent oil, and earth. These being found in greater quantities in bohea than in green teas, those who have very sensible and elastic nerves must be seized with a greater tremor after drinking the former than the latter. The continual and regular influx of the nervous juices is stopped by their component fibres being contracted from the roughness and restringency of such decoctions. The force of the heat, or the brain's propulsion of its nervous juice, being inferior to the resistance of the whole ramified fibres thus encreased by the sudden contraction and unequal motion, the flow of the animal spirits must be greatly impeded and disordered. In fact, the influx suffers a suspension, until the fibres, by relaxing again, admit their empty tubes to receive their appropriated liquids. Thus even green tea must, especially if taken strong and often, stop the natural circulation of humours, and produce the attendant defects of depression of spirits, deficiency of secretion, loss of appetite, decrease of strength, waste of body, and, finally, a total want of effective vigour in all the animal functions. But, as above observed, bohea tea possessing in greater quantity the pernicious ingredients, the vessels are thrown into momentary spasms and convulsive vibrations, by the relaxing power of the narcotic salts, and the contracting force of the astringent oil and earth. And here it must be noticed, that oil mixed with salt is rendered astringent: thus all vegetables, where a mixture of both prevails, are reckoned stimulating. The narcotic power of the salt is derived from its hindering the flux of the animal spirits through the nerves.

The stomach and bowels being weakened by the above causes, windy complaints or flatulencies are consequently produced. This caused Dr. Whytt, in his advice to patients afflicted with such diseases, to desire they would abstain from India tea, as one of the flatulent aliments chiefly to be avoided.