Popular Science Monthly 



715 



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 



