SE-CRE'TION (L. _secer'no_, _secre'tum_, to separate). The process of separating from the blood some essential important fluid; which fluid is also called a secretion.

SEM-I-CIR'CU-LAR Ca.n.a.lS. A portion of the internal ear.

SEN-SA'TION. The perception of an external impression by the nervous system; a function of the brain.

SEN-SI-BIL'I-TY, GENERAL. The power possessed by nearly all parts {262} of the human body of recognizing the presence of foreign objects that come in contact with them.

SE'RUM (L.). The watery const.i.tuent of the blood, which separates from the clot during the process of coagulation.

SKEL'E-TON (Gr.). The bony framework of an animal, the different parts of which are maintained in their proper relative positions.

SPEC'TRO-SCOPE (from _spec'trum_ and [Greek: skopeo], _scopeo_, to examine the spectrum). An instrument employed in the examination of the spectrum of the sun or any other luminous body.

SPHYG'MO-GRAPH (Gr. [Greek: sphugmos], _sphugmos_, the pulse, and [Greek: grapho], _grapho_, to write). An ingenious instrument by means of which the pulse is delineated upon paper.

STA'PES (L.). Literally, a stirrup; one of the small bones of the tympanum, or middle ear, resembling somewhat a stirrup in shape.

SYM-PA-THET'IC SYSTEM OF NERVES. A double chain of nervous ganglia, connected together by numerous small nerves, situated chiefly in front of and on each side of the spinal column.

SYN-O'VI-A (Gr. [Greek: sun], _sun_, and [Greek: oon], _oon_, resembling an egg). The lubricating fluid of joints, so called because it resembles the white of egg.

SYS'TO-LE (Gr. [Greek: sustello], _sustello_, to contract). The contraction of the heart, by which the blood is expelled from that organ.

TAC'TILE (L. _tac'tus_, touch). Relating to the sense of touch.

TEM'PO-RAL (L. _tem'pus_, time, and _tem'pora_, the temples). Pertaining to the temples; the name of an artery: so called, because the hair begins to turn white with age in that portion of the scalp.

TEN'DON (L. _ten'do_, to stretch). The white, fibrous cord or band by which a muscle is attached to a bone; a sinew.

TET'A-NUS (Gr. [Greek: teino], _teino_, to stretch). A disease marked by persistent contractions of all or some of the voluntary muscles; those of the jaw are sometimes solely affected: the disorder is then termed locked-jaw.

THO'RAX (Gr. [Greek: thorax], _thorax_, a breastplate). The upper cavity of the trunk of the body, containing the lungs, heart, etc.; the chest.

THY'ROID (Gr. [Greek: thureos], _thureos_, a shield). The largest of the cartilages of the larynx; its angular projection in the front of the neck is called "Adam's apple."

TRA'CHE-A (Gr. [Greek: trachus], _trachus_, rough). The windpipe, or the largest of the air-pa.s.sages; composed in part of cartilaginous rings, which render its surface rough and uneven.

TRANS-FU'SION (L. _transfun'do_, to pour from one vessel to another). {263} The operation of injecting blood taken from one person into the veins of another; other fluids than blood are sometimes used.

TRICH-I'NA SPI-RA'LIS. (L.) A minute species of parasite or worm, which infests the flesh of the hog, and which may be introduced into the human system by eating pork not thoroughly cooked.

TYM'PA-NUM (Gr. [Greek: tumpanon], _tumpanon_, a drum). The cavity of the middle ear, resembling a drum in being closed by two membranes, and in having communication with the atmosphere.

U'VU-LA (L. _uva_, a grape). The small pendulous body attached to the back part of the palate.

VAS'CU-LAR (L. _vas'culum_, a little vessel). Pertaining to, or containing blood-vessels.

VE'NOUS (L. _ve'na_, a vein). Pertaining to, or contained within a vein.

VEN-TI-LA'TION. The introduction of fresh air into a room or building, in such a manner as to keep the air within it in a pure condition.

VEN-TRIL'O-QUISM (L. _ven'ter_, the belly, and _lo'quor_, to speak). A modification of natural speech by which the voice is made to appear to come from a distance. The ancients supposed that the voice was formed in the belly; hence the name.

VEN'TRI-CLES of the heart. The two largest cavities of the heart, situated at its apex or point.

VER'TE-BRAL COLUMN (L. _ver'tebra_, a joint). The back-bone, consisting of twenty-four separate bones, called vertebrae, firmly jointed together; also called the spinal column and spine.

VES'TI-BULE. A portion of the internal ear, communicating with the semicircular ca.n.a.ls and the cochlea; so called from its fancied resemblance to the vestibule or porch of a house.

VIL'LI (L. _vil'lus_, the nap of cloth). Minute thread-like projections found upon the internal surface of the small intestine, giving it a velvety appearance.

VIT'RE-OUS (L. _vi'trum_, gla.s.s). Having the appearance of gla.s.s; applied to the humor occupying the largest part of the cavity of the eyeball.

VIV-I-SEC'TION (L. _vi'vus_, alive, and _se'co_, to cut). The practice of operating upon living animals, for the purpose of studying some physiological process.

VOCAL CORDS. Two elastic bands or ridges situated in the larynx; they are the essential parts of the organs of the voice.