This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Thyme: a low shrubby plant; consisting of numerous (lender tough (talks, with little roundish leaves in pairs, and loose spikes, on the tops, of purplish or whitish labiated flowers, whose upper lip is nipt at the extremity, the lower divided into three nearly equal segments.
1. Thymus Pharm. Edinb. Thymum vulgare folio tenuiore C. B. Thymus vulgaris Linn. Common thyme: with upright (talks, and dark brownish green somewhat pointed leaves; a native of the southern parts of Europe, common in our gardens, and flowering in June and July.
This herb is a moderately warm pungent aromatic. To water it imparts, by infusion, its agreeable smell, but only a weak taste, with a yellowish or brown colour: in distillation, it gives over an essential oil, in quantity about an ounce from thirty pounds of the herb in flower, of a gold yellow colour if distilled by a gentle fire, of a deep brownish red if by a strong one, of a penetrating smell resembling that of the thyme itself, but less grateful, in taste exces-sively hot and fiery: the remaining decoction, infpiffated, leaves a bitterish, roughish, subsa-line extract. The active matter, which by water is only partially dissolved, is by rectified spirit dissolved completely; though the tincture, in colour blackish-green, discovers less of the smell of the thyme than the watery infusion: the spirit brings over in distillation a part of its flavour, leaving an extract of a weak smell and of a penetrating camphorated pungency.
2. Serpyllum Pharm. Edinb. Serpyllum vul-gare minus C. B. Thymus Serpyllum Linn. Mother-of-thyme: with trailing stalks, and ob-tuse leaves: growing wild on heaths and dry paslure grounds. This also is an elegant aromatic plant, similar to the foregoing species, but milder, and in flavour rather more grateful. Its essential oil is both in smaller quantity and less acrid, and its spirituous extract comes greatly short of the penetrating warmth and pungency of that of the other. It is said to afford an agreeable distilled water, more durable, but less active and penetrating than pepper-mint (a). Both the leaves themselves, and their spirituous tincture, are of a bright green colour, without any thing of the brown or blackish hue of those of common thyme.
3. Thymus citratus Serpyllum foliis citri odore C. B. Lemon-thyme: in appearance differing little from the second sort, of which Linnaeus makes it a variety, except that it is more upright and more bushy; a native of dry mountainous places, common in gardens, and flowering as the others in July. This species is less pungent than the first sort, more so than the second, and much more grateful than either: its smell in particular is remarkably different, approaching to that of lemons. Distilled with water, it yields a larger quantity than the other sorts, of a yellowish very fragrant oil of the lemon flavour, containing nearly all the medicinal parts of the plant, for the remaining decoction is almost insipid as well as inodorous. It gives over also with rectified spirit its finer odorous matter; a less agreeable flavour, and a moderate warmth, remaining in the spirituous extract.
(a) Cullen, Mat, Med.