A vivid eruption of papulae, somewhat analogous to the prickly heat, appears in our own climate, on the arms, hands, face, and neck of labourers, and other persons who use violent exercise during the hot months of summer. It produces a sensation of tingling, a smarting rather than of itching, and disappears in a short time without any particular consequences. See Willan on Cutaneous Diseases.

In veterinary medicine the term lichen is applied to a species of leprosy and warts which grow on horses' legs.

In botany it is called liverwort, and is a floriferous and seminiferous moss, whose flowery little heads are furnished with many grains, variously shaped, producing as they ripen several little monopetalous flowers. The seeds, which are small, flat, and orbicular, are contained in some peculiar open capsules, resting upon the plane of the leaves, and are sometimes found in the same plant that bears the little heads, sometimes in other plants of the same species. Besides these flowery heads, in some species there are umbellated heads of different figures, which produce neither flower nor seed. The pedicles of both species are for the most part naked, and proceed from no vagina. The leaves are of an herbaceous consistence, and of an indeterminate figure, widely spread--ing, and running out into various roots from their back part. Every plant under the name of lichen is. warm and astringent; and this term is applied to the muscus pyxidatus, hepatica vulgaris, etc. besides the succeeding.

Lichen arboreus pullus, muscus crustae. Tree liverwort, lichen {Meatus Lin. Sp. Pl. 1622, grows on trees, and is used instead of the pulmonaria arbo-rea. It is astringent, and chiefly used in pulmonary haemorrhages.

Lichen cinereus. Ash coloured ground liverwort; lichen caninus Lin. Sp. Pl. 1616. It consists of roundish thick leaves, divided about the edges into obtuse segments, flat above, of a reticular texture below, fastened to the earth by small fibres, of an ash grey colour, by age turning darker or reddish. It grows on commons and open heaths, spreads quickly on the ground, and is found at all times of the year, but supposed to be most active from the end of autumn to the winter. A powder, called pulvis antilyssus, used to be formed of two parts of this moss, and one of black pepper: 3 i. ss. in half a pint of cow's milk, for four mornings successively, was to be taken fasting. (See Hydrophobia.) It has now fallen into disrepute; and does not appear to be possessed of any useful degree of medicinal virtue.

Lichen islandicus, Lin. Sp. Pl. 1611; lichen trrrestris; lichenoides; and rigidum; eryngo leaved, eatable, Iceland lichen, is a native of Britain, and grows both in Scotland and Wales. It is foliaceous, erect, large; leaves crowded, connected, about two inches high, stiff when dry, but soft and pliant when moist: they are variously divided, without order, into broad distinct segments, turned in at the edges, and fringed with short strong bristles; the upper surface is smooth, concave, shining, of a pale green, or chestnut colour, but red at the base; the under is smooth and whitish, a little pitted and sprinkled with very minute black warts: the fructifications are large, of a reddish colour, and placed on the lobes of the leaves. This plant is extremely mucilaginous, has a bitter and somewhat astringent taste, and is considered as a laxative and an anthelmintic in its recent state: but its bitterness and aperient quality are in a great measure destroyed by drying, or a slight infusion. The Icelanders make a flour of it, called fialgras, either by first washing and cutting the plant into small pieces, or by drying it, putting it into a bag, which is well beaten, and working it into flour by stamping. This is tolerably agreeable and grateful food. As a medicine, Scopoli and Haller recommend it in coughs and consumptions; and it has proved efficacious in dysentery and diarrhoea. Dr. Hertz found it so successful in dysentery, that after the repeated administration of emetics and cathartics he seldom used any other medicine, to which he occasionally added opium. Dr. Crichton recommends it in phthisis attended with haemoptoe and pituitous or mucous discharges; and thinks he has found it of considerable service. It is given in decoction, made by boiling one ounce and an half in a quart of milk, over a slow fire, exactly a quarter of an hour. The dose is about a pint in the day. If the milk disagrees, water may be used. This medicine has lately become fashionable; but we have only found it a mild nutrient. The bitter is apparently of the narcotic kind, and at times is cold and heavy on the stomach. If this is taken away by a slight previous infusion, a mucilaginous, or rather a farinaceous matter, only remains, without apparently any distinguishing property. At Berlin it seems to have been used with differentsuc-cess. M. J. C Fritze thinks it a valuable medicine, even when purulent matter is expectorated; and he added to the decoction, either in milk or water, the flowers of St. John's wort and coltsfoot. F. Fritze, in his Clinical Annals, chiefly confines its utility to its mildly nutritious powers; and Scheffer was usually unsuccessful with it, except in recent, apparently catarrhal, cases.

Lichen pyxidatus, Lin. Sp. Pl. 1619, (from pixis, a cup, in consequence of its bearing little cups). See

Muscus Pyxidatus.