Dr. Willan defined, an extensive eruption of papulæ affecting adults, connected with internal disorder, usually terminating in scurf, recurrent, not contagious. The varieties of lichen he considers under the denominations of lichen simplex, lichen agrius, lichen pilaris, lichen lividus, and lichen tropicus. 1. The lichen simplex usually commences with head-ache, flushing of the face, loss of appetite, general languor, and increased quickness of the pulse. Distinct red papulæ arise first about the cheeks and chin, or on the arms; and in the course of three or four days the same appearance takes place on the neck, body, and lower extremities, accompanied with an unpleasant sensation of tingling, which is somewhat aggravated during the night. In about a week the colour of the eruption fades, and the cuticle begins to separate; the whole surface is at length covered with scurfy exfoliations, which are particularly large, and continue longest in the flexures of the joints. The duration of the complaint is seldom in any two cases alike; ten, fourteen, seventeen, or sometimes twenty days intervene betwixt the eruption and the renovation of the cuticle. The febrile state, or rather the state of irritation at the beginning of this disorder, is seldom considerable enough to confine the patient to the house. After remaining five or six days, it is generally relieved on the appearance of the eruption. This, as well as some other species of the lichen, occurs about the beginning of summer or in autumn, more especially affecting persons of a weak and irritable habit; hence women are more liable to it than men. Lichen simplex is also a frequent sequel of acute diseases, particularly fever and catarrhal infiammation, of which it seems to produce a crisis. In these cases the eruption has been termed by medical writers scabies critica. Many instances of it are collected under that title by Sauvages, Nosol. Method. Class x. Order 5. Impetigines. 2. The lichen agrius is preceded by nausea, pain in the stomach, head-ache, loss of strength, and deep-seated pains in the limbs, with fits of coldness and shivering, which symptoms continue several days, and are sometimes relieved by the papillous eruption. The papulæ are distributed in clusters, or often in large patches, chiefly on the arms, the upper part of the breast, the neck, face, back, and sides of the abdomen; they are of a vivid red colour, and have a redness, or some degree of inflammation, diffused round them to a considerable extent, and attended with itching, heat, and a painful tingling. Dr. Willan has observed, in one or two cases where it was produced from imprudent exposure to cold, that an acute disease ensued, with great quick. ness of the pulse, heat, thirst, pains of the bowels, frequent vomiting, head-ache, and delirium. After these symptoms had continued ten days, or somewhat longer, the patient revered, though the eruption did not return. diffuse redness connecting the papulæ, and the tendency to become pustular, distinguish the lichen agrius from the lichen simplex, and the other varieties of this complaint, in which the inflammation does not extend beyond the basis of the papula, and which terminates in scurf or scales. 3. Lichen pilaris. This is merely a modification of the first species of lichen, and, like it, often alternates with complaints of the head or stomach, in irritable habits. The peculiarity of the eruption is, that the small tubercles or asperities appear only at the roots of the hairs of the skin, being probably occasioned by an enlargement of their bulbs, or an unusual fulness of the blood-vessels distributed to them. This affection is distinguishable from the cutis anserina, by its permanency, by its red papulæ, and by the troublesome itching or tingling which attends it. If a part thus affected be violently rubbed, some of the papulæ enlarge to the size of wheals, but the tumor soon subsides again. The eruption continues more or less vivid for about ten days, and terminates, as usual, in small exfoliations of the cuticle, one of which surrounds the base of each hair. This complaint, as likewise the lichen agrius, frequently occurs in persons accustomed to driuk largely of spirituous liquors undiluted. 4. Lichen lividus. The papulæ characterising this eruption are of a dark red or livid hue, and somewhat more permanent than in the foregoing species of lichen. They appear chiefly on the arms and legs, but sometimes extend to other parts of the body. They are finally succeeded, though at very uncertain periods, by slight exfoliations of the cuticle, after which a fresh eruption is not preceded nor attended with any febrile symptoms. It principally affects persons of a weak constitu tion, who live on a poor diet and are engaged in laborious occupations. Young persons, and often children living in confined situations, or using little exercise, are also subject to the li chen lividus; and in them the papulæ are generally intermixed with the petechiæ, or larger purple spots, resembling vibices. This circumstance points out the affinity of the lichen lividus with the purpura or land-scurvy, and the connexion is further proved by the excit ing causes, which are the same in both complaints. The same method of treatment is likewise successful in both cases. They are presently cured by nourishing food, moderate exercise in the open air, along with the use of Peruvian and vitriolic acid, or the tincture of muriated steel. 5. Lichen tropicus. By this term is expressed the prickly heat, and papulous eruption, almost universally affecting Europeans settled in tropical climates. The prickly heat appears without any preceding disorder of the constitution. It consists of numerous papulæ, about the size of a small pin's head, and elevation so as to produce a considerable roughness of the skin. The papulæ are of a vivid red colour, and often exhibit an irregular form, two or three of them being in many places united together; but no redness or inflammation extends to the skin in the interstices of the papulæ. LICHEN. (from lichen, a tetter or ringworm, because it was formerly supposed to be of use in curing this complaint.) In botany, a genus of the class cryptogamia, order algæ. Fructification in tubercles or shields, invested with their proper cortical receptacles, on a variously formed and constructed frond. Nearly six hundred species, of which between two and three hundred are indigenous to our own country. See Botany, Pl. CVII. They may be thas subdivided: A. Receptacle, or outer-coat of the fructification compact, hardish, of a different substance from the frond. 1. Those, of this subdivision, with black shields; flat, oblong, elliptic, linear, or variously formed, opening longitudinally, simple or confluent or branched, with a crustaceous frond, are called Opegrapha. II. Those with shields or tubercles sessile, hardish, orbicular, or deformed by mutual pressure; their discs flattish or becoming convex, often with a thickish margin, nearly the colour of the disc; frond crustaceous, foliaceous, stellate, or umbilicate, are denominated Lecidea, The lecidea are again subdivided. 2. Frond crustaceous, uniform. These are named Catillaria. 6. Frond crustaceous, imbricate, or lobed. Lepidoma. 7. Frond foliaceous, stellate, fibrous underneath. Saphenaria. 3. Frond foliaceous, peltate. Omphalaria. III. Tubercles hardish, mostly seated on a stalk, becoming shield-like and margined; frond crustaceous. These are called Calicium. IV. Tubercles sessile, convex, or hemispheric, black, variously plaited, closed, irregularly bursting when old; frond foliaceous, membranaceous, or cartilaginous. These are named Gyrophora. V. Tubercles nearly globular, black, with from one to four round, hollow cells, each covered with a wart-like deciduous lid; frond crustaceous. Bathelium. B. Receptacle, or outer coat of the fructification, of the same substance and colour as the frond. 1. Receptacle compound: the outer raised II. Tubercles roundish, terminal, inclosing at first covered with the frond, at length tral-coloured globules, which eventually fall off; frond crustaceous, papillary, or branched. Isidium. IV. Shields immersed in the frond, concave, invested with a margin from the frond, frond crustaceous, uniform. Urceolaria. V. Shields thickish, raised above the frond with a distinct margin of the colour and substance of the frond: frond various. Parmelia. This is again subdivided. a. Frond crustaceous, uniform. Lecanaria. 6. Frond crustaceous, composed of imbricate scales. Psoroma. 7. Frond crustaceous, flat, with a lobed or radiate circumference. Placodium. 8. Frond foliaceous, somewhat membranous, depressed, stellate, more or less imbricate, fibrous underneath. Circinaria. . Frond leafy, somewhat coriaceous, with vague, lax expanded lobes, villous underneath. Lobaria. . Frond foliaceous, gelatinous, variously formed. Collema. n. Frond leafy, nembranous, depressed; segments linear, somewhat imbricate, vaulted, or inflected at the tips. Physica. 9. Frond leafy, membranous, tufted, Janciniate-branched, fistular; branches cylindrical, obtuse, bearing the shields at their tips. Cenotea. .. Frond leafy, membrano-cartilaginous; tufted, segments rather erect, linear, tapering, longitudinally channelled underneath. Canalicularia. x. Frond somewhat leafy, cartilaginous, or leathery segments erect or pendent, flat or cylindrically compressed, fitted, tapering, branched, nakell, glabrous. Polymesia. A. Frond filamentous, somewhat cartilaginous, branched; filaments nearly cylindric, pendulous, or diffuse. Tricharia. VI. Frond leafy, membranous, or somewhat coriaceous, lobed; bearing membranous, sessile, flat, orbicular shields on the upper surface, and mealy shields like white or yellowish pits among the down on the under surface. Shita. VII. Shields thin, membranous, sessile, generally flat, closely attached by their margins to the frond: frond leathery, or membranous; mostly with downy or fibrous veins underneath the fertile lobes long ascending and naked beneath. Peltidea. VIII. Shields flat, sessile, attached to the frond by their margin, frond leafy, membrano-cartilaginous, lobed, rigid, glabrous, naked on both sides. Cetraria. IX. Shields terminal, flat, peltate, cartila ginous, becoming irregular, and a little convex, with the margin reflected; frond cartilaginous, rigid, nearly solid, spongy within, in shrub-like tufts, with acute branches. Cornicularia. X. Tubercles sessile, terminal and scattered, somewhat turbinate, at the first margined, at length convex, covered with a mem C brane: frond solid, rather woody, ceru lescent, branched, roughish and fibrous. Stereocaulon. XI. Tubercles terminal, mostly on pedicels, becoming convex or cup-like, simple or clustered, covered with a thin solid membrane: frond crustaceous or leafy. Baomices. This again is subdivided into five inferior partitions, which, being of less moment, we shall not stay to describe. The chief species: 1. L. candelarius. Yellow farinaceous lichen; common upon walls, rocks, boards, and old pales. 2. L. parellus. Craw-fish eye lichen; found also on walls and rocks, but not very frequently. 3. L. parietinus. Common yellow wall lichen; very common upon walls, rocks, tiles of houses, and trunks of trees. 4. L. prunastri. Common ragged hoary lichen; growing upon all sorts of trees parasitically; but generally most white and hoary on the sloe, or old palm trees, or the tops of old pales. 5. L. caninus. Ash-coloured ground liverwort; found on the ground among moss at the roots of trees in shady places, sometimes on heaths and in stony places. The lichen eine rens terrestris of the dispensatories, with a weak, faint smell, and a sharpish taste. It was for a long time highly extolled as a medicine of singular virtue, in preventing and curing that dreadful disorder, which is produced by the bite of rabid animals, but now deservedly forgotten. See PULVIS ANTILYSSUS. 6. L. cocciferus, for which see Muscus PYXIDATUS. 7. L. islandicus. The medicinal qualities of the lichen islandicus have lately been so well established at Vienna, that this plant is now admitted into the materia medica of the Edinburgh pharmacopoeia. It is extremely nucilaginous, and to the taste is bitter, and somewhat astringent. Its bitterness, as well as the purgative quality which it manifests, in its recent state, are in a great measure dissipated on drying, or may be extracted by a slight infusion in water, so that the inhabi tants of Iceland convert it into a tolerably grateful and nutritive food. An ounce of this lichen, boiled a quarter of an hour in a pint of water, yielded seven ounces of a mucilage as thick as that procured by the solution of one pint of gum arabic in three of water. The medical virtues of this lichen were pro. bably first learned from the Icelanders, who employ it in its fresh state as a laxative; but when deprived of this quality and properly propared, we are told that it is an efficacious remedy in consumptions, coughs, dysenteries, and diarrhoeas. Scopoli secins to have been the first who of late years called the attention of physicians to this remedy in consumptive disorders; and further instances of its success te related by Herz, Cramer, Tromsdorff, 1... Paniky, Stoll, and others, who bear ny of its cfficacy in most of the other complaints above mentioned. Dr. Herz says, that since he first used the lichen in dysentery, he found it so successful, that he never had occasion to employ any other remedy; it must be observed, however, that cathartics and emetics were always repeatedly administered before he had recourse to the lichen, to which he also occasionally added opium. Dr. Crichton informs us, that during seven months' residence at Vienna, he had frequent opportunities of seeing the lichen islandicus tried in phthisis pulmonalis at the general hospitals, and confesses," that it by no means answered the expectation he had formed of it." He adds, however," from what I have seen, I am fully convinced in my own mind, that there are only two species of this disease where this sort of lichen promises a cure. The two species I hint at are, the phthisis haemoptoica, and the phthisis pituitosa or mucosa. In several cases of these I have seen the patients so far get the better of their complaints as to be dismissed the hospital cured, but whether they remained long so or not I cannot take upon me to say." That this lichen strengthens the digestive powers, and proves extremely nutritions, there can be no doubt; but the great medicinal efficacy attributed to it at Vienna will not readily be credited at London. It is commonly given in the form of a decoction; an ounce and a half of the lichen being boiled in a quart of milk. Of this a tea-cupful is directed to be drank frequently in the course of the day. If milk disagree with the stomach, a simple decoction of the lichen in water is to be used. Care ought to be taken that it be boiled over a slow fire, and not longer than a quarter of an hour. The Iceland moss grows also on various mountains both of the Highlands and Lowlands of Scotland. Its fronds are nearly erect, about two inches high, and stiff when dried. 8. L. pyxidatus. PYXIDATUS. Cup-moss. See Muscus 9. L. roccella. See RoCCELLA. 10. L. saxatilis. See USNEA. LICHFIELD, or LITCHFIELD, a small city of England, in the county of Stafford, situated on a small river, which runs into the Trent, about three miles from the town. It is a county of itself, with power of holding assizes, and determining cases of life and death. It was erected into an archbishopric in the latter part of the eighth century by king Offa, but soon after it was reduced to a bishopric, under the archbishopric of Canterbury. In the year 1075, the see was removed to Chester; and in 1102, to Coventry; but, not long after, was restored to Lichfield, united with Coventry. The cathedral was first built in the year 300, and has been several times rebuilt and enlarged, particularly by Bishop Hacket, after the Restoration, in the last century, and in the year 1759, when it underwent a thorough repair. Here are three other churches, and formerly there was a castle, now destroyed. The south side of the river is called the city, and the other the close. When the civil war broke out, the close was garrisoned for the king, |