Pres-by-o´pi-a (Gr. πρέσβυς, presbus, old, and ὤψ, ops, the eye). A defect of the accommodation of the eye, caused by the hardening of the crystalline lens; the "far-sight" of adults and aged persons.

Proc´ess (L. proce´do, proces´sus, to proceed, to go forth). Any projection from a surface. Also, a method of performance; a procedure.

Pty´a-lin (Gr. πτύαλον, ptualon, saliva). The peculiar organic ingredient of the saliva.

Pul´mo-na-ry (L. pul´mo, pulmo´nis, the lungs). Pertaining to the lungs.

Pulse (L. pel´lo, pul´sum, to beat). The striking of an artery against the finger, occasioned by the contraction of the heart, commonly felt at the wrist.

Pu´pil (L. pupil´la). The central, round opening in the iris, through which light passes into the depths of the eye.

Py-lo´rus (Gr. πυλωρός, puloros, a gate-keeper). The lower opening of the stomach, at the beginning of the small intestine.

Re´flex Action. An involuntary action of the nervous system, by which an external impression conducted by a sensory nerve is reflected, or converted into a motor impulse.

Res-pi-ra´tion (L. res´piro, to breathe frequently). The function of breathing, comprising two acts: inspiration, or breathing in, and expiration, or breathing out.

Ret´i-na (L. re´te, a net). The innermost of the three tunics or coats of the eyeball, being an expansion of the optic nerve.