There is one circumstance, however, that renders it more difficult to investigate the certain effects of Tea; which is, the great unwillingness that most people shew, to giving us a genuine account of their uneasy sensations after the free use of it; from a consciousness that it would be extremely imprudent to continue its use, after they are convinced from experience that it is injurious.
That it produces watchfulness in some constitutions is most certain, when drank at evening in considerable quantities. Whether warm water, or any other aqueous liquor, would have the same effect, is not certain.
That it enlivens, refreshes, exhilarates, is likewise well known. From all which circumstances it would seem, that Tea contains an active penetrating principle, speedily exciting the action of the nerves; in very irritable constitutions, to such a degree as to give very uneasy sensations, and bring on spasmodic affections: in less irritable constitutions, it rather gives pleasure, and immediate satisfaction, though not without occasionally producing some tendency to disagreeable tremours and agitation.
The finer the Tea, the more obvious are these effects. It is perhaps for this, amongst other reasons, that the lower classes of people, who can only procure the most common, are in general the least sufferers. I say, in general, because even amongst them there are many who actually suffer much by it: they drink it as long as it yields any taste, and, to add to its flavour, for the most part hot; and thus the quantity which they take, and the degree of heat in which it is drank, conspire to produce in them, what the finer kinds of Tea effect in their superiors.
It ought not, however, to pass unobserved, that in a multitude of cases the infusions of our own herbs, sage for instance, mint, baum, even rosemary, and valerian itself, will sometimes produce similar effects, and leave that sensation of emptiness, agitation of spirits, flatulence, spasmodic pains, and other symptoms, that are met with in people, the most of all others devoted to Tea.
Besides the injuries which the stomach sustains, by taking the infusion of Tea extremely hot; it is not improbable but the teeth also are affected by it. Professor Kalm, in his Travels into North America, observes, that such of the inhabitants as took their Tea and food in general, in this state, were frequently liable to lose half their teeth at the age of twenty, without any hopes of getting new ones. This cannot be attributed to the variations of weather in that clime, because the Indians who enjoy the same air, but take their viands almost cold, were to a great age possessed of fine white teeth;as were likewise the Europeans who first settled in America, before the use of Tea became general. It was no less remarkable, that the Indian women, who had accustomed themselves to drink this infusion after the European fashion, had likewise lost their teeth prematurely, though they had formerly been quite sound[83]. Kalm does not appear to suspect any injury to the teeth from the sugar used with the Tea.