As the custom of drinking Tea is become general, every person may be considered as a judge of its effects, at least so far as it concerns his own health; but, as the constitutions of mankind are various, the effects of this infusion must be different also, which is the reason that so many opinions have prevailed upon the subject.
Many, who have once conceived a prejudice against it, suffer it to influence their judgement too far, and condemn the custom as universally pernicious. Others, who are no less biassedon the other extreme, would make their own private experience a standard for that of all, and ascribe the most extensive virtues to this infusion. This contrariety of opinion has been particularly maintained among physicians[75]; which will ever be the case, while mere suppositions are placed in the room of experiments and facts impartially related.
Some physicians, however, avoid both extremes; who, without commending it, or decrying it universally, admit its use, while they are not insensible of the injuries it may produce. It requires no small share of sagacity to fix the limits of good and harm in the present case: multitudes of all ages, constitutions, and complexions, drink it freely, during a long life, without perceiving any ill effects. Others, again, soon experience many inconveniences from drinking any considerable quantity of this infusion.
It is difficult to draw certain conclusions from experiments made on this herb. The parts which seem to produce these opposite effects are very fugitive. We become acquainted chiefly with the grosser parts by analysis. I made the following experiments with considerable care; but, I own, they inform us not sufficiently wherein consists that grateful relaxing sedative property, which proves to the generality of mankind so refreshing; nor from whence it is, that others feel from the pleasing beverage so many disagreeable effects. Accurate observation would instruct us in this difficult investigation, more than simple experiments on the subject itself.
I took an equal quantity of an infusion of superfine green Tea, and of common bohea Tea, made equally strong; and also the same quantity of the liquor remaining after distillation (Sect.III.I.), and of simple water; into each of which, contained in separate vessels, I put two drachms of beef, that had been killed about two days.
The beef, which was immersed in the simple water, became putrid in forty-eight hours; but the pieces in the two infusions of Tea, and in the liquor remaining after distillation, shewed no signs of putrefaction, till after about seventy hours[76].
Into strong infusions of every kind of green and bohea Tea that I could procure, I put equal quantities of salt of iron (sal martis), which immediately changed the several infusions into a deep purple colour[77].
It is evident from these experiments, that both green and bohea Tea possess an antiseptic (ExperimentI.), and astringent power (ExperimentII.), applied to the dead animal fibre.