Refraction

{re-frak* ’shun) [re, back; frangere, to break]. I. The act of refracting or bending back. 2. The deviation of a ray of light from a straight line in pa ing obliquely from one transparent medium to another of different density. 3. The state of refractive power, especially of the eye; the ametropia or emmetropia present. R., Angle of, the angle formed by a refracted ray of light with the perpendicular at the point of refraction. REFLEXES.— Continued. Effect Produced. Significance. Reflex movements. Swallowing. Contraction of toes. Dilatation of pupil. Contraction of iris. Absent in basal mening i- Dilatation of pupil. tis, etc*. Contraction of scapular mus- Shows integrity of cord becles. tween upper two or three dorsal and lower two or three cervical nerves. from centers in the spinal cord. it at i on of the skin. Reflex contraction of gastroc- Considered as a delicate nemius. test of heightened spinal irritability. Involuntary flexion of foot, Met with in cases in which then flexion of leg, and, the knee-jerk and other lastly, flexion of the thigh on tendon-reflexes are the pelvis. strongly developed. Retraction of bulb oca ver no us Occurs in health. portion. A series of jerking move- In the late rigidity of ments of the hand. hemiplegia. R., Double, the power po e ed by certain substances, as Iceland-spar, of dividing a ray of light and thus producing a double image of an object. R., Dynamic, the static refraction of the eye, plus that secured by the action of the accommodative apparatus. R., Index of, the refractive power of any substance as compared with air. It is the quotient of the angle of incidence divided by the angle of refraction of a ray pa ing through the substance. R., Static, that of the eye when accommodation is at rest. 551