Anatomy, physiology and hygiene for high schools . s. In very close work a stop should be made every ten minutesafter a person is thirty years old; a few seconds will suffice. 2 Drs. Nicol and Mossop of Edinburgh conducted a series of experiments on eachother, examining the eye by means of the ophthalmoscope while the system was tinderthe influence of various drugs. They found that the nerves controlling the delicateblood vessels of the retina were paralyzed by a dose of about a tablespoonful of brandy. 254 PHYSIOLOGY AND HYGIENE vibration in the air, which are transmitted to the ear. Whenthes
Anatomy, physiology and hygiene for high schools . s. In very close work a stop should be made every ten minutesafter a person is thirty years old; a few seconds will suffice. 2 Drs. Nicol and Mossop of Edinburgh conducted a series of experiments on eachother, examining the eye by means of the ophthalmoscope while the system was tinderthe influence of various drugs. They found that the nerves controlling the delicateblood vessels of the retina were paralyzed by a dose of about a tablespoonful of brandy. 254 PHYSIOLOGY AND HYGIENE vibration in the air, which are transmitted to the ear. Whenthese vibrations in the ear are taken up by the sense organand converted to nerve impulses, which are carried to thebrain by the auditory nerve, we have the sensation of hear the bell ring. The organ of hearing is the ear. The ear consists of theexternal ear, the middle ear, and the internal ear. The external ear consists of a cartilage shell covered byconnective tissue and skin. This shell collects the sound. External ear Semicircularcanals. Section of ear, showing auditory canal, middle ear,internal ear, and Eustachian tube. From this outer shell a canal runs inward into the temporalbone. At the inner end of the canal is a membrane, thetympanum, which stretches across the canal and shuts itoff from the middle ear. The canal is lined with skin, anda substance called wax is secreted in it from glands in itswalls. The middle ear is a cavity in the temporal bone. The THE SPECIAL SENSES 255 drmn, or hjmpanum (Greek timipanom, a drum ), shuts it offfrom the outei* ear. Froin its inner side a tube, the Eusta-chian tube, kjuls to the upper part of the pharynx. We canfeel the air go into the ear by tliis tube sometimes when weswallow. In tli(^ inner wall are two openings, the fotestra (Latinfenestra, window) ovalis (oval) and fenestra rotunda(round), which lead to the cavity of the inner ear. Theyare closed eacli ])y a membrane. Stretching from the tympanum to the fenestra ovalis
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