EPICYCLE. 146 EPIDEEMIS. the motion of the moon about the sun actually is. Bv assuming proper proportions between the radii rent circle and the epicycle, and be- tween the velocities of the two motions, it was found possible to account for the motions of the plani EP'ICY'CLCTD (Gk. em, epi, upon + m/oc, lcyklos, circle + el8oc,eidos, form). If a circle moves on the outside of the circumference of another circle, every point in the plane of the first circle describes an epicycloid. This curve first appeared in a work of Diirer's (1525), but tlie name is due to Roeiuer ( 1672) . It has many remarkable properties, and is also interesting from a practical point of view. The teeth of cog-wheels must, as shown by Desargues, have an epicycloidal form, in order that friction may be minimum. The term formerly included the curve described when the moving circle was on the inside of the other, but this 'inner epiey- cloid' is now called the 'hypocycloid.' For the equation of this curve and references to its his- tory, see Cycloid; and for a more extensive bib- liography, consult the Intermediaire des Mathe- maticiens (Paris, 1898, 1899). EPTDAMTJUS. See Dukazzo. EP'IDATJ'RTJS (Lat., from Gk. 'ErlSavpos, Epidauros). A town of ancient Greece, on the Saronic Gulf, in the northeast part of Argolis, situated on a small promontory, in latitude 37° 38' north, longitude 23° 10' east. The early history of Epidaurus is involved in myth, but numerous religious connections with Attica lend probability to the legend of an original Ionian population. Later, it was a Dorian city, closely connected with, but not subject to, Argos. The greatest prosperity of Epidaurus seems to have been in the early period, when it was a member of the Calaurian Amphictyony, and was said to have controlled .-Egina and colonized Cos. Ca- lydnus. and Nisyrus. Its power afterwards de- clined, and during the historical period if owed it- importance chiefly to the pi of the celebrated sanctuary of ^Esculapius, which at- '1 patients from all parts of II. world. The site of this temple a tin sur- rounded by mountains, about Bvi miles west oi the town, still called Hieron (the sanctuary). Epidaurus (modern Greek, Epidhavro) is now a small village, with scarcely a hundred inhabit ants, employed for the most part in raising ibles for the Athenian market. The plain surrounding the village is productive and highly cultivated. Here, in January, 1822. a congress from all parts of ('! recce assembled, and pro- ted the constitution, known as the 'Consti- tution of Epidaurus.' Consult: Gardiner, New Chapters in Greek History (London, 1892); Diehl, ! Greece ( London, 1 893) . The detailed descriptions may be found in Cawadias, I pidauri i t Inns. 1893) : Defrasseand Pari 1 895 l magnificently illustrated with conjectural restorations of the ' i ailias.Ti hpbvTov' OK-t)- irioD <> 'EiriJoupip I tlim 1900). EPIDEMIC (Lai Gk. among i be peopli epi, upon h Sfj/inr, ipp] led i o diseases which ap| a1 intervals and spread ovei a certa in a largi i of the world, ier i people,
■ ( q.v. ) , and remain permanently in a locality. Cholera ' is epidemic in certain parts of Europe, at inter- vals subsiding and disappearing; while it re- mains endemic in India. Probably all diseases which are epidemic in various parts of the world are endemic in certain localities, and the epi- demics are brought by travelers from these localities; or follow commerce under favoring conditions, such as starvation during famine, debility dependent upon exposure to miasmata after inundations; swarming and migration of insects which carry contagion, etc. Drainage and paving of streets result in checking and eradicating an epidemic of malaria in a town. Opening the pavements and tunneling the streets afford harbors in damp spots and puddles for mosquitoes, which propagate rapidly, become infected with the Plasmodium of malaria, and transmit the micro-organism to human beings; and thus an epidemic of malaria is started. Epi- demics of typhoid fever are almost invariably traced to one or a few eases of the disease, from whose excrement drinking-water has became pol- luted. Epidemics are due, primarily, to dis- semination of bacterial germs, though in some diseases of the contagious class (such as scarlet fever and smallpox) the causative germs have not yet been isolated. They must be checked, therefore, by bacteriological precautions. It is difficult to explain the cause of certain cycles in which epidemics appear to move, regularly recur- ring in certain localites ; but in all cases pre- cautions should be taken to quarantine people entering a port from an infected country, and clothing and all merchandise should be disin- fected. Serum therapy (q.v.) promises a pro- tection against many epidemic diseases, as well as treatment during disease. Epidemics of nervous diseases have appeared at times in the history of the world: as of chorea (q.v.), or of dancing mania. Under the leadership of a person afflicted with paranoia (q.v.), many people of unstable mental equilib- rium have been dominated by suggestion (q.v.), and the results have been crusades, persecution of 'witches,' epidemics of suicides, etc. Con- sult Hecker. Epidemics of the Middle Ages, trans, by Babington (London, 1849). See Climate; Contagion ; Infection ; Cholera ; Typhoid Fe- ver, etc. EPIDEMIC CEREBRAL MENINGITIS. See Meningitis. EP'IDEN'DRUM (Neo-Lat., from Gk. brt, epi, upon + Sivipov, dendron, tree). A genus of strong-growing, long-stemmed epiphytal orchids, of which nearly 600 species have been found in Central America alone. Though some of the spe- cies produce showy blossoms, the majority have flowers of rather unattractive appearance, various shades of greenish purple being common. The group is of special interest, however, from its in- creasing popularity in hybridizing with the gaudier, weaker, short-stemmed, and more diffi- cultly cultivated members of other genera, e.g. Cattleya and l.a-lia. The operation is of fairly easy performance and often results in vigorous plants, long steins, graceful racemes, and attrac- t ivc flowers. EP'IDER'MIS (Lat., from Gk. imdepftis, up- per skin, from M, epi, upon + |, '/7'", derma, skin). The cuticle, or scarf skin, a semi-trans- pareni membrane, containing neither vessels nor
