THE SENSES 



the nostrils closed, walk into the open air, then inhale fresh air. At the 

 moment of the inhalation of fresh air the ammonia is again perceptible. 

 Repeat with bergamot, rose water, etc. 



6. The Limits of the Sense of Hearing. Use a set of tuning forks 

 for the purpose, and determine the lowest vibration per second which can be 

 perceived as sound. Determine the highest limits in the same way. 



7. Acuteness of the Sense of Hearing. Listen to the vibrations of 

 a tuning fork, or, better, to the ticking of a watch which is moved back and 

 forth from the ear. Measure the distance at which it can just be distin- 

 guished. This experiment should be performed with the person blindfolded, 

 and extraneous noise should, of course, be suppressed. 



70. Dynamic and Static Functions of the Labyrinth. Maxwell working 

 with sharks and Woodworth with pigeons have demonstrated new points 

 in the physiology of the semicircular canals and of the utriculus and saccu- 

 lus. Compensating motions are produced on stimulating the sense organs 

 of the semicircular canal, easily demonstrated in the shark and pigeon. 

 Destruction of these sense organs results in loss of co-ordination of types 

 depending upon the organs affected. The semicircular canals must be 

 operated in pairs to induce complete loss of co-ordination in the particular 

 plane. 



a. Operate on the Pigeon. Remove the sensory ampullae of the hori- 

 zontal semicircular canals on each side. The operation is performed under 

 careful ether anesthesia and must be aseptic throughout. Quick recovery 

 occurs. The animal loses the power of controlling movements, the com- 

 pensatory movements, in the horizontal plane. It will walk round and 

 round in a circle, or move the head without the usual quick co-ordinative 

 control of the skeletal musculature. 



b. Remove the right upper and the left lower ampullae in a second 

 bird. Study its disturbances of co-ordination as in the first. 



In the case of these pigeons, particular attention must be given to 

 supplying water and feed for the first few days following the operation. The 

 birds will soon learn to take care of themselves. They do not recover 

 power of co-ordination as generally supposed. This was shown by the 

 demonstrations of Dr. Woodworth at the St. Louis meeting of the Amer- 

 ican Medical Association, 1922. Dr. Woodworth's pigeons had been 

 operated many months before. 



8. Refraction. Light passes out from a luminous point in straight 

 lines so long as the line of propagation is in a medium of uniform density. 

 If the rays pass from a transparent mediurn of one density into a second 

 medium of different density, they will usually be turned out of their course, or 

 refracted. If the rays enter the second medium at right angles to its surface, 

 they will continue in straight lines, but if they enter at any other angle they 

 will be refracted. If the second medium is denser than the first, the rays will 



