Emulsion (Lat. _emulgere_, to milk). Oil in a finely divided state, suspended in water. Enamel (Fr. _émail_). Dense material covering the crown of a tooth. Endolymph (Gr. ἔνδον, within, and Lat. _lympha_, water). The fluid in the membranous labyrinth of the ear. Endosmosis (Gr. ἔνδον, within, and ὠθέω, to push). The current from without _inwards_ when diffusion of fluids takes place through a membrane. Epidemic (Gr. ἐπί, upon, and δέμος, the people). An extensively prevalent disease. Epiglottis (Gr. ἐπί, upon, and γλόττις, the entrance to the windpipe). A leaf-shaped piece of cartilage which covers the top of the larynx during the act of swallowing. Epilepsy (Gr. ἐπίληψις, a seizure). A nervous disease accompanied by fits in which consciousness is lost; the falling sickness. Ether (Gr. αἰθήρ, the pure, upper air). A narcotic poison. Used as an anæsthetic in surgical operations. Eustachian (from an Italian anatomist named Eustachi). The tube which leads from the throat to the middle ear, or tympanum. Excretion (Lat. _excerno_, to separate). The separation from the blood of the waste matters of the body; also the materials excreted. Exosmosis (Gr. ἔξω, without, and ᾀθέω, to push). The current from within _outwards_ when diffusion of fluids takes place through a membrane. Expiration (Lat. _expiro_, to breathe out). The act of forcing air out of the lungs. Extension (Lat. _ex_, out, and _tendo_, to stretch). The act of restoring a limb, etc., to its natural position after it has been flexed or bent; the opposite of _flexion_. Fauces. The part of the mouth which opens into the pharynx. Fenestra (Lat.). Literally, “a window.” Fenestra ovalis and fenestra rotunda, the oval and the round window; two apertures in the bone between the tympanic cavity and the labyrinth of the ear. Ferment. That which causes fermentation, as yeast. Fermentation (Lat. _fermentum_, boiling). The process of undergoing an effervescent change, as by the action of yeast; in a wider sense, the change of organized substances into new compounds by the action of a ferment. It differs in kind according to the nature of the ferment. Fiber (Lat. _fibra_, a filament). One of the tiny threads of which many parts of the body are composed. Fibrilla. A little fiber; one of the longitudinal threads into which a striped muscular fiber can be divided. Fibrin (Lat. _fibra_, a fiber). An albuminoid substance contained in the flesh of animals, and also produced by the coagulation of blood. Flexion (Lat. _flecto_, to bend). The act of bending a limb, etc. Follicle (Lat. dim. of _follis_, a money bag). A little pouch or depression. Fomentation (Lat. _foveo_, to keep warm). The application of any warm, medicinal substance to the body, by which the vessels are relaxed. Foramen. A hole, or aperture. Frontal Sinus. A blind or closed cavity in the bones of the skull just over the eyebrows.