Page:Popular Science Monthly Volume 91.djvu/731

 Popular Science Monthly

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���The Result of the Pass-Point Test The applicant is turned ten times in ten seconds to the left or right with eyes closed. The chair is brought to a sudden stop and his hand is seized by the examiner. He is told to raise his arm and to come back and touch the examiner's finger. This he cannot do for several seconds if the static labyrinth of his ear is normal

his skull. Hence it is that the applicant is carefully tested to ascertain whether or not he has a normally reacting laby- rinth.

Study the diagram on page 712 and you will see that the labyrinth is made up of three semicircular canals. Each canal presides over the movement of the .head in the plane in which it runs.

The Wonderful Spirit Level in Your Head

Like the spirit level of a carpenter, these canals contain a fluid, which is known as the endolymph. Move the head in one direction and the endolymph moves in the opposite direction, thus acquainting you with your movements even though your eyes are closed. This telegraphing is done by way of the cerebellum (the coordinating center of the brain) to the muscles, the eyes and the higher centers of the brain. Thus, if you are normal, you are able to maintain an even keel. Only a very few drops of endolymph are provided — so small

��Putting Him Through the Falling Test The applicant is placed in a chair with his head for- ward approximately ninety degrees to bring the superior canal of the labyrinth of his ear on the level plane of turning. After having been turned five times in ten seconds to the left, for example, he feels that he is falling to the right when he sits up with his eyes closed

are the canals. But these few drops are vitally essential to a man in maintaining a normal station in space, with eyes closed, or in any situation in which he cannot judge his position by sight.

You may gather from what you have thus far read that the Government considers the static labyrinth of the utmost im- portance in the examination of men who want to join the aviation corps. The function of the static labyrinth will be readily understood if we remember that it is made up of canals containing fluid and that each canal runs in a different direction and presides over the movements of the head in the plane in which it runs. If you move your head around the neck as a pivot, the fluid in the horizontal or external canal moves in the opposite direction. If you move your head from side to side, the fluid in the superior canal moves in the opposite direction. If the head is moved backward or forward, the fluid in the posterior canal moves in the opposite

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