successors of the Greek astronomers, down to Tycho Brahé, continued, therefore, to increase the number of epicycles, setting one circle upon another, until the hypothesis, in itself complicated, became still more so, and made the simplicity of the Copernican system at once striking.

EPICY CLOID is the name of a peculiar curve. When a circle moves upon a straight line, any point in its circumference describes a Cycloid (q. v.); but if the circle moves on the convex circumference of another circle, every point in the plane of the first circle describes an epicycloid; and if on the concave circumference, a hypocycloid. The circle that moves is the generating circle; the other, the base. The describing point is not necessarily in the circumference of the generating circle, but may be anywhere in a radius or its prolongation. This curve was first investigated by the Danish astronomer Römer. It has many remarkable properties, and is even useful in the practical arts. The teeth of wheels in machinery must have an epicycloidal form, in order to secure uniformity of

movement.

EPIDA'MNUS. See DURAZZO.

EPIDAU'RUS, a town of ancient Greece, on the eastern shore of the Peloponnesus, in the district of Argolis, was situated on a small promontory, 15 stadia in circumference, in the Saronic Gulf, in lat. 37° 38' N., long. 23° 10′ E. During the most prosperous period of Grecian history, E. was an independent state. It was colonised first, it is supposed, by Carians (hence the older name of Epicarus, according to Aristotle), and afterwards by Ionians, but was subsequently invaded by a Dorian army under Deiphontes, the son-in-law of Temenus the Heracleide. This force dethroned Pityreus, the Ionian king of E., compelled him and his citizens to retire to Athens, and inaugurated the Dorian rule, which preserved the ascendency at E. during the whole of the historical period. The form of government was originally monarchical, but after many vicissitudes, it eventually became and remained oligarchical. At an early period, E. became one of the chief commercial cities of the Peloponnesus. It colonised the islands of Cos, Calydnus, and Nisyrus, as well as the town of Ægina, which, during the 6th c., attracted all its commerce from the then declining mother-city. E. was chiefly famous for its temple of Esculapius, to which patients resorted from all parts of the Hellenic world, seeking cures for their diseases. The site of this temple was a plain surrounded by mountains, about 5 miles west of the town, and which is still called Hieron, the sanctuary. E. had also numerous temples, among which were those of Artemis, Dionysus, Aphrodite, and Hera, and a magnificent theatre, at present in a more perfect state of preservation than any in the Peloponnesus, and with sufficient accommodation for 12,000 spectators.

E. (modern Greek, Epidavro) is now a small village, with scarcely 100 inhabitants, employed for the most part in raising vegetables for the Athenian market. The plain surrounding the village is productive and highly cultivated. Here, in January 1822, a congress from all parts of Greece assembled, and promulgated the constitution, known as the constitution of Epidaurus.

EPIDEMIC (Gr. epi, upon, and demos, the people), a disease which attacks numbers of persons in one place simultaneously or in succession, and which in addition is observed to travel from place to place, often in the direction of the most frequented lines of communication. Many epidemic diseases are also contagious, and all of them suggest the necessity of carefu inquiry into the ventilation, drainage, food,

drink, and habits of the persons liable to be affected. In presence of an epidemic, it is proper to take unusual precautions to preserve the public health (see HEALTH, PUBLIC), and not unfrequently the organisation of a regular house-to-house visitation of the locality is calculated to do much good, by directing the minds of the poor and ignorant to their duties in respect to themselves and to each

other. See ENDEMIC for further observations on this subject; also CONTAGION, INFECTION, FEVER, CHOLERA, &c.

A

EPIDEMIC MENTAL DISEASES. When we consider how ordinary and normal thoughts and emotions spread from one man to many, and sway multitudes to the same views and actions, it is no longer a mystery that morbid conditions of the mind should become at times no less epidemic than physical diseases. Such, at least, is the fact. mental disorder may spread from man to man, and may involve whole nations. It depends for its propagation, like an epidemic disease, first upon external circumstances, and secondly, upon the peculiar condition or constitution of the individuals affected. Like the bodily affection, the causes which provoke the insanity and the tendency to be affected may have been in process of development for years. Both attack the weak rather than the strong; both exist for a season, and disappear. In the case of the mental malady, the external influences-those which constitute the moral atmosphere -are ignorance or imperfect knowledge, the power of one mind over another, the influence of language, the diffusion of particular opinions, the tendency to imitate. It is probable, however, that physical causes exercise an important influence in the production of such general mental conditions. In 1842 and 1814, there occurred in Germany and France, among the military, epidemics of meningitis with delirium, or inflammation of the membranes of the brain, when no moral factors were at work, but when diet, temperature, &c. were. But even where the origin cannot be so distinctly traced, the co-oper ation of external as well as psychical agents may be legitimately predicated. It would accordingly be illogical to limit the production of the Dancing Mania (q. v.), which occasionally, during several centuries, swept over Europe, to the reaction succeeding the dread of the end of the world, which had previously prevailed epidemically. An examination of about a hundred manifestations such as that alluded to, collected from various sources, demonstrates that not merely the intoxication of joy, but the most absurd forms of belief-that dreams, delusions, superstitions, corruptions of language, all instincts and passions, even movements and cries, may assume the form, and, to a certain extent, may follow the laws of epidemic diseases. In far-distant ages, there are records of a histrionic plague, when, after a summer of intense heat, all conceived themselves players, and traversed the streets, and sunk and died, repeating verses, and exhibiting extravagant gesticulations; of whole communities being stricken with nightmare, which was so general as to be supposed and called contagious. There have been epidemics of homicidal and suicidal mania. age, hundreds are found possessed by Satan; in another, larger numbers converted into wolves; and in recent times, the leaping ague of Forfarshire, and outbursts of pyromania in various places, remind us that there may be still in the constitution of the human mind, and in the education and the habits of life prevailing, elements capable of realising the catastrophe suggested by Bishop Butler's question: What is to prevent a whole nation becoming mad? The instances of epidemic mental disease recorded in the following table, have been selected from a

In one

There appears to be no guarantee that the present and future generations shall be exempted from similar visitations, except in the universal diffusion of knowledge and sound thinking, for it is invariably in the darkness of ignorance or in the twilight of imperfect knowledge that the moral plague comes.Hecker's Epidemics of the Middle Ages; Calmiel, De la Folie considerée sous le Point de Vue Pathologique, Philosophique, Historique et Judiciaire, depuis la Renaissance des Sciences en Europe jusq'au dixneuvième Siècle, &c.; Psychological Journal, and passim.

EPIDERMIS (Gr. epi, upon, and derma, the skin), a semi-transparent membrane, containing neither vessels nor nerves, and everywhere forming an external covering to the corium or true skin. See SKIN. The epidermis is called in ordinary language the scarf-skin. It consists of two layers, chemically and morphologically distinct-viz., the mucous layer, which lies immediately upon the corium, and the horny layer, which forms the outermost surface of the body.

mucosum

The mucous layer (known formerly as the rete 8. Malpighianum) is of a whitish or slightly brown tint (in the Negro, dark gray or black), and is composed of small soft cells. The

a, a, papilla of the cutis; b, deepest intensely coloured layer of perpendicularly elongated cells of the mucous layer; c, upper stratum of the same layer; d, horny layer.

innermost of these cells, resting on the surface of the corium, are elongated and arranged perpendicularly; upon these follow elongated or roundish cells in many layers, which, in proportion to their distance from the corium, acquire, from their mutual

pressure, a polygonal form, which may even be recognised in individual cells.

All the cells in the mucous layer are nucleated vesicles distended with fluid, and likewise containing minute granules, which diminish in number in the more external cells.

The horny layer forms the external semi-transparent part of the epidermis, which in the white races is colourless, and is composed almost wholly of uniform cells, metamorphosed into plates or scales. The deepest plates in some degree resemble the uppermost cells of the mucous layer; but in the second or third layer we find the flattening commence; till at length, after a gradual series of modifications, we have the hard, horny scales which off with more or less rapidity, and replaced by occur on the surface, where they are regularly cast those beneath them.*

The colour of the epidermis differs in different persons and in different parts of the body. It is deepest around the nipple, especially in women during pregnancy and after they have borne children. A more or less dark pigment is often deposited, in persons who are exposed to the sun, in the face, neck, back of the hands, &c. These tints are not

produced by special pigment-cells, but are seated in the common cells of the mucous layer, round whose nuclei granular pigment is deposited. In the Negro and the other coloured races, it is also only the epidermis which is coloured, while the corium completely resembles that of Europeans. The perpendicular cells (see b in the figure) are the darkest, and form a sharply marked fringe at the edge of the clear corium. To these succeed brown cells, which accumulate in the depressions between the papille, and as we approach the horny layer, we have yellowish cells. The horny layer of the Negro also inclines to a yellow or brownish

tint.

Morbid coloration of the epidermis (freckles, mother's marks, &c.) is produced in the same way as the colour of the Negro's skin. Numerous instances of partially or entirely white Negroes and of black Europeans, not as a consequence of change of climate but as an abnormal condition of the skin, are on record.

The thickness of the epidermis varies extremely. While upon the cheeks, brow, and eyelids, it varies it ranges from d to a line, and on the sole of the fromth to th of a line, on the palm of the hand foot sometimes even exceeds a line. In some parts of the body the horny layer is thicker thar the mucous; in other, the mucous is the thicker of the two. As the chief use of the epidermis is that of

cast off in a more or less entire state, a new one being *In reptiles and amphibians, this layer is periodically previously formed beneath it; and in man, desqua nation in large patches often occurs after certain diseases, especially scarlatina.

face in water, or otherwise closing up the mouth and nostrils, or by dragging upon a tightened neckcloth. Care should be always taken to avoid these accidents by keeping the epileptic as much as possible within view of persons acquainted with his condition, and able to give such assistance as may be required; as well as by warning the patient himself to avoid all places in which a fall would be especially dangerous. But when an unskilled person happens to witness a fit of epilepsy, he will do well to remember that beyond the simplest and most obvious precautions against the dangers mentioned above, there is literally nothing to be done; and any attempt to rouse the patient by violent stimuli, as ammonia applied to the nostrils, or by dashing water in the face, or, still more, by administering medicines hastily recommended by the ignorant and thoughtless, is almost certain to do more harm than good. The tongue should be looked to, a piece of cork or other gag being, if necessary, inserted between the teeth; the patient should be then placed on a mattress or other soft place near the ground; his neckcloth should be removed, and the dress loosened round the chest; the head should be, if possible, a little raised, and a free circulation of air maintained (this last precaution being very apt to be neglected in case of a crowd); with these things doue, it may be safely affirmed that in the vast majority of epileptic cases nothing has been left undone which will conduce to recovery. The ordinary course of the fit (which usually lasts from five to twenty minutes altogether) is as follows: the convulsions gradually diminish in intensity, and the patient passes into a state of deep but motionless stupor, with dilated pupils, and sometimes, but not always, with snoring or noisy breathing; the foaming at the mouth ceases, the colour gradually returns, and this state leads to recovery through a more or less protracted, but apparently natural sleep, the patient, on awaking, being often quite unconscious that he has been the subject of any anxiety, or, indeed, in any unusual condition whatever. Although in all cases of true epilepsy there is a stage of complete Coma (q. v.), or unconsciousness, yet the fit is often very transient, and but little attended by convulsion, being also less sudden than above described, and not necessarily causing a fall to the ground; in some cases, also, fits of greater intensity are preceded by certain premonitory symptoms or peculiar sensations, which act as warnings to the patient himself, and lead him to place himself in a position of safety on the approach of the paroxysm. Having in view these distinctions (which are certainly of considerable practical importance), the French language, both popular and scientific, has adopted the terms of grand mal and petit mal (i. e., great and little evil), as characterising the more and less dangerous forms of epilepsy respectively. The sensations which precede the fit in some epileptics have been termed in Latin the aura (ie., breath) epileptica, from their supposed resemblance to a current of cold air passing over the body, and proceeding from the extremities towards the head. This description does not, however, hold good in all cases; and not unfrequently, as mentioned above, there is no aura, or unusual sensation of any kind, preceding the fit. It must be mentioned, however, as bearing on treatment, and as being quite within the bounds of popular medicine, that some of the most ancient authorities assert strongly the power of a tight bandage, placed suddenly upon the limb in which the aura begins, to cut short, or even to prevent altogether, the fit of epilepsy. Although this alleged fact has often been regarded as doubtful, it has never been altogether discredited, and has of late years been brought into renewed notice

by good observers. It is even maintained that such a bandage, placed experimentally upon one of other of the limbs, and tightened on the approach of a fit, has been found effective in some cases in which there was no distinctly local sensation; and epileptics have been repeatedly convinced of the propriety of habitually wearing a bandage loosely applied upon the arm, which they have been able, by carefully watching their own sensations, and by being watched in turn by others, to get tightened at the proper time. There is no doubt room for fallacy in these observations, but they may safely be commended to notice, as involving no possible risk of mischief, and as far more worthy of extended trial than the great majority of popular remedies in epilepsy.

But the fit and its treatment form only a part of the anxieties which arise out of a case of epilepsy. The ultimate danger of the disease has little rela tion to the severity of the individual fits, except in the modified sense explained above; the frequency of the attacks being apparently much more apt to influence the duration of life than their character. Indeed, although epileptics may survive several severe paroxysms at distant intervals, and recover in the end with an apparently unbroken constitution, it rarely happens that very frequently repeated attacks, even of the petit mal, are unattended by some permanent depreciation of the powers of mind or of body. The most frequent, perhaps, of all the more serious consequences of confirmed epilepsy is Insanity (q. v.), sometimes assuming the form of acute mania or monomania following the attacks, but quite as frequently tending to gradual imbecility without any acute seizure. Sometimes the development of the epileptic insanity, or dementia, is attended by palsy, and other indications of structural disorder of the brain; in other instances, no such consequences occur, and the brain after death may be found to have very little tangible disease, or only such disease as is found in numerous other cases of functional derangement. Very often, even when the mind remains tolerably entire, there is loss of memory, and a certain want of acuteness and depression of spirits, which unfit the individual for the regular business of life. Disorders of the digestion are also not uncommon; and there is frequently a want of tone and vigour in all the bodily func tions, which communicates a habitual expression of languor and reserve to the epileptic. Added to this, it can hardly be matter of surprise that the knowledge of his infirmity should deeply influence the mind of the epileptic, and produce a distaste for active occupations, especially for such as expose him to more than ordinary observation.

The causes and the radical cure of epilepsy are almost equally involved in mystery. It has been supposed by some to be dependent on an increased aflux of blood to the brain; while by other observers and pathological authorities it has been attributed, with about equal force of reasoning, to precisely the opposite condition. Certain cases undoubtedly depend upon organic disease, as tumours or injuries to the brain and its membranes, more especially near the surface. Local sources of irritation in ather parts of the body have also been supposed to be exciting causes of epilepsy; and cases recorded in which the disease has been cured by the amputation of a finger or the division of a nerve. The attention of recent observers has been especially directed to the medulla oblongata and Spinal Cord (q. v.), as being the most probable physiological seats of a disease so decidedly marked by convulsive movements. But as yet little more than the most vague theoretical inferences can be drawn from their researches as to the cause either of the morbid

are