EXERCISE 96 



The semicircular canals are our balancing organs, as changes in their positions result in 

 a stimulation of nerve endings in their lining. 



Problem. How sensitive is an animal to changes in its position ? 



What to use. A live frog in a battery jar ; lampblack ; absorbent cotton ; vaseline. 



What to do. 1. When the frog is at rest, slowly rotate the jar to right or left (3O-45) without 

 shaking it ; reverse the movement. Note reactions of frog. Hold the jar up so that you can see the side 

 of the animal, and tilt the jar forward and backward, noting reaction. Hold the jar up so that you face 

 the frog, and tilt it to the right and to the left, noting reactions. 



2. To see whether any of these responses are influenced by sight, mix a little vaseline and lamp- 

 black, and rub the mixture into a piece of moist absorbent cotton. With this pad you can blindfold the 

 frog without hurting or irritating it. (Repeat the displacements as in i .) 



Record. Describe the responses of the frog to changes in bodily position, and try to answer the 

 question in the Problem. 



Questions. 1. What evidence did you discover that the frog is influenced by the direction from 

 riiich the light strikes it ? 



2. How would you find out whether the frog would behave in the same way if it ttsed its eyes only ? 



3. What practical use can be made of the fact that some people are more sensitive to changes in 

 position than others ? 



4. What evidence is there that, besides the semicircular canals, other organs and sensations help 

 us to keep erect and walk straight ? 



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