Ptyalin (Gr. s?a???, saliva). A ferment principle in _saliva_, having power to convert starch into sugar.

Pulse (Lat. _pello, pulsum_, to beat). The throbbing of an artery against the finger, occasioned by the contraction of the heart. Commonly felt at the _wrist_.

Pupil (Lat. _pupilla_). The central, round opening in the iris, through which light pa.s.ses into the interior of the eye.

Pylorus (Gr. p???????, a gatekeeper). The lower opening of the stomach, at the beginning of the small intestine.

Reflex (Lat. _reflexus_, turned back). The name given to involuntary movements produced by an excitation traveling along a sensory nerve to a center, where it is turned back or reflected along motor nerves.

Renal (Lat. _ren_, _renis_, the kidney). Pertaining to the _kidneys_.

Respiration (Lat. _respiro_, to breathe frequently). The function of breathing, comprising two acts,--_inspiration_, or breathing in, and _expiration_, or breathing out.

Retina (Lat. _rete_, a net). The innermost of the three tunics, or coats, of the eyeball, being an expansion of the optic nerve.

Rima Glottidis (Lat. _rima_, a c.h.i.n.k or cleft). The _opening_ of the glottis.

Saccharine (Lat. _saccharum_, sugar). The group of food substances which embraces the different varieties of sugar, starch, and gum.

Saliva. The moisture, or fluids, of the mouth, secreted by the salivary glands; the spittle.

Sarcolemma (Gr. s???, flesh, and ??a, a husk). The membrane which surrounds the contractile substance of a striped muscular fiber.

Sclerotic (Gr. s??????, hard). The tough, fibrous, outer coat of the eyeball.

Scurvy. s...o...b..tus,--a disease of the general system, having prominent skin symptoms.

Sebaceous (Lat. _seb.u.m_, fat). Resembling fat; the name of the oily secretion by which the skin is kept flexible and soft.

Secretion (Lat. _secerno_, _secretum_, to separate). The process of separating from the blood some essential, important fluid; which fluid is also called a _secretion_.

Semicircular Ca.n.a.ls. Three ca.n.a.ls in the internal ear.

Sensation. The perception of an external impression by the nervous system.

Serum. The clear, watery fluid which separates from the clot of the blood.

Spasm (Gr. spas??, convulsion). A sudden, violent, and involuntary contraction of one or more muscles.

Special Sense. A sense by which we receive particular sensations, such as those of sight, hearing, taste, and smell.

Sputum, pi. Sputa (Lat. _spuo_, _sputum_, to _spit_). The matter which is coughed up from the air pa.s.sages.

Stapes. Literally, a stirrup; one of the small bones of the middle ear.

Stimulant (Lat. _stimulo_, to p.r.i.c.k or goad on). An agent which causes an increase of vital activity in the body or in any of its parts.

Striated (Lat. _strio_, to furnish with channels). Marked with fine lines.

Styptics (Gr. st?pt???? astringent). Substances used to produce a contraction or shrinking of living tissues.

Subclavian Vein (Lat. _sub_, under, and _clavis_, a key). The great vein bringing back the blood from the arm and side of the head; so called because it is situated underneath the _clavicle_, or collar bone.

Superior Vena Cava (Lat., upper hollow vein). The great vein of the upper part of the body.

Suture (Lat. _sutura_, a seam). The union of certain bones of the skull by the interlocking of jagged edges.

Sympathetic System of Nerves. A double chain of nervous ganglia, situated chiefly in front of, and on each side of, the spinal column.

Symptom (Gr. s??, with, and p?pt?, to fall). A sign or token of disease.

Synovial (Gr. s??, with, and ???, an egg). The liquid which lubricates the joints; joint-oil. It resembles the white of a raw egg.

System. A number of different organs, of similar structures, distributed throughout the body and performing similar functions.

Systemic. Belonging to the system, or body, as a whole.

Systole (Gr. s?st????, to contract). The contraction of the heart, by which the blood is expelled from that organ.

Tactile (Lat. _tactus_, touch). Relating to the sense of touch.

Tartar. A hard crust which forms on the teeth, and is composed of salivary mucus, animal matter, and a compound of lime.

Temporal (Lat. _tempus_, time, and _tempora_, the temples).

Pertaining to the temples; so called because the hair begins to turn white with age in that portion of the scalp.

Tendon (Lat. _tendo_, to stretch). The white, fibrous cord, or band, by which a muscle is attached to a bone; a sinew.

Teta.n.u.s (Gr. te???, 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 lockjaw.

Thorax (Gr. ???a?, a breast-plate). The upper cavity of the trunk of the body, containing the lungs, heart, etc.; the chest.

Thyroid (Gr. ??????, a shield, and e?d??, form). The largest of the cartilages of the larynx: its projection in front is called "Adam's Apple."

Tissue. Any substance or texture in the body formed of various elements, such as cells, fibers, blood-vessels, etc., interwoven with each other.

Tobacco (Indian _tabaco_, the tube, or pipe, in which the Indians smoked the plant). A plant used for smoking and chewing, and in snuff.

Trachea (Gr. t?a???, rough). The windpipe.

Tragus (Gr. t?????, a goat). The eminence in front of the opening of the ear; sometimes hairy, like a goat's beard.

Transfusion (Lat. _transfundo_, to pour from one vessel to another).

The operation of injecting blood taken from one person into the veins of another.