of albuminous
matter.

Ptyalin (Gr. sialon, 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 passes into the interior of the eye.

Pylorus (Gr. pulouros, 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 chink 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. sarxi, flesh, and lemma, a husk). The membrane which
surrounds the contractile substance of a striped muscular fiber.

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

Scurvy. Scorbutus,--a disease of the general system, having prominent skin
symptoms.

Sebaceous (Lat. _sebum_, 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 Canals. Three canals 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. spasmos, 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 sme