Page:Popular Science Monthly Volume 91.djvu/732

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��Popular Science Monthly

���direction. And so it is that the flowing of the endolymph within these canals acquaints us with the direction of our head movements.

Testing Ears to See If You Can Fly

Now since the testing of the static labyrinth is obviously de- pendent upon the movement of the fluid or endolymph within the canal, some means must be em- ployed for causing the endolymph to flow within the canal. Hence, a special kind of re- volving chair is used which is known as the ."Jones' modifi- cation of the Barany chair." The appli- cant is seated in the chair and directed to incline his head thirty degrees for^ ward. That brings the horizontal canal within the level plane of turning. With eyes closed, the applicant is whirled ten times in twenty seconds in this position. Then the chair is stopped,

and the applicant is told to look at a dis- tant object. The visual, disturbance result- ing from the experiment is known as the nystagmus. The duration of his nystagmus is noted with a stop watch ; it should last in a normal person about twenty-six seconds. The nystagmus may be described as a rhythmic to and fro motion of the eyes, consisting of two move- ments — a slow movement in one direction which is followed at once by a rapid move- ment in the opposite direction. This nystag- mus lasts only so long as the fluid within the canal tested continues to flow artificially.

The applicant is now turned in the op- posite direction and tested in like manner.

Still seated in the revolving chair, un- changed in position and with eyes closed, the applicant is tested for "pass-pointing." He extends his right arm and touches the examiner's hand with his forefinger. From this position he raises his arm to a vertical

��position and attempts to bring his finger back and touch the examiner's hand again. He is now turned ten times in ten seconds to the left or right. The chair is stopped and his hand is seized by the examiner. He is told to raise his arm and come back and touch the examiner's finger as before. He cannot do it if his static labyrinth is normal. The underlying principle of the fore- going test is not dif- ficult to understand. Since the applicant was turned tp the right, in this case, and the chair stopped, the fluid in the horizontal canal continued to move to the right after the chair was stopped — continued to move, in other words, in the direction of turn- ing. Hence, the applicant feels that he is being turned to the left, and in trying to locate the finger of the exam- iner, he naturally pass-points to the right.

��The Result of the Falling Test

After having been turned five times in ten seconds to the right or left, with eyes closed, the applicant feels that he is falling to the right when he sits up with his eyes closed. He tries to overcome this and actually falls to the

���The Three Testing Positions

The whirling tests are made with the applicant seated with his head either at an angle of thirty degrees forward or at ninety degrees. The position sixty degrees backward is usually used for a douche or caloric test when the whirling tests are unsatisfactory

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