This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This is the herb of Mentha viridis, an herbaceous perennial plant, like the above species a native of Europe, and naturalized in this country, where it is also cultivated for use.
The herb differs from peppermint in having lanceolate, nearly sessile, and lighter-coloured leaves, and elongated, pointed spikes of flowers, whence the name of spearmint was derived. The brighter greenness of the leaves probably gave origin to the specific name of viridis or green. The plant is often called simply mint; and, when that term is used without a qualifying epithet, it may be understood as applied to the present species. Its smell and taste are analogous to those of peppermint, but peculiar, and by some preferred. Others, however, and probably the greater number, give precedence to the mentha piperita.
The active principle is the volatile oil; though, as in peppermint, there is a small proportion of tannic acid and of a bitter principle. The oil closely resembles that of the other species.
The same resemblance extends to the medical properties and uses of the two mints; but the spearmint is thought to be somewhat the weaker. The same preparations are used, and in about the same doses. Those of spearmint recognized by the U. S. Pharmacopoeia, are the Volatile Oil (Oleum Menthae Viridis, U. S.), of which the dose is from two to six drops; the Spirit or Essence of Spearmint (Spiritus Menthae Viridis, U. S.; Tinctura Olei Menthae Viridis, U. S. 1850), of which from twenty to forty drops may be given; and Spearmint Water (Aqua Menthae Viridis, U.S., Br.), made and used in the same manner as the corresponding preparation of peppermint. An infusion of spearmint was formerly directed by the Dublin College, made in the proportion of about half an ounce of the herb to a pint of water. Though abandoned in the British Pharmacopoeia, it may nevertheless be useful, when the oil is not at hand. It may be given without special limitation of the dose.
There are several aromatics of minor importance, consisting of the herb or leaves of plants, which, though not extensively used, are yet sufficiently so to require a brief notice, and may, perhaps, be best introduced in a subordinate position here.