174 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



6. Elimination of Sweet and Bitter. Apply a 5 per cent, decoction 

 of gymnema sylvestris to a limited area of the tongue. Twenty to 

 thirty seconds later rinse the mouth thoroughly and test the taste with 

 the solutions used for Experiment 2. What solutions remain effective? 



7. Structure of Olfactory Cells. Study hitologic preparations of the 

 olfactory area. 



8. Distribution of Olfactory Cells. Place a glass funnel over some 

 odoriferous substance. Insert the tip of the funnel first into the lower 

 posterior and then into the upper anterior region of the nasal cavity. 

 Which region is the more sensitive to the odor? Where is the olfactory 

 area located? 



9. Olfactory Latency. Smell oil of cloves held close to the nose, and 

 determine the time intervening between this act and the perception 

 of the sensation. Give a reason for this latency. 



10. Olfactory Fatigue. Smell tincture of camphor, tincture of 

 iodin, or oil of cloves with one nostril until the olfactory cells have 

 been fatigued. Note the time it takes for the fatigue to set in and 

 for the acuteness of smell to be re-established. 



11. Qualitative Changes Before Exhaustion. Inhale oil of cloves 

 through one nostril and observe the changes which occur in the quality 

 of the sensation before it ceases. 



12. "Threshold Value" of Sounds. Determine the greatest dis- 

 tance at which the subject can still hear the tick of a watch placed on 

 the level of his right or left ear, the other ear having been closed with 

 cotton. To avoid inattention the subject should shut his eyes. When 

 just at the threshold of audibility the sound varies greatly in its intensity. 



Place the handle of a vibrating tuning-fork upon the head. Note 

 the intensity of the sound, and then remove the fork quickly before the 

 sound ceases completely. Observe that the change to complete silence 

 seems much greater than the apparent low intensity of the sound would 

 justify. 



13. Auditory Fatigue. Insert the ends of a Y-shaped rubber tube 

 into the openings of the ears. Place a vibrating tuning-fork upon the 

 tube in such a way that the sounds seem equally intense to both ears. 

 Remove the tuning-fork. After a brief interval occlude the tube on one 

 side by pinching it, and place the vibrating tuning-fork in its former 

 position. When the sound has nearly ceased to be audible, open the 

 pinched tube. The sound now appears to be much stronger in the 

 rested ear than in the other. 



14. Location of Tones. Place the handle of a vibrating tuning-fork 

 upon the top of the head. In what part of the head does the sound 

 seem to be localized? Close one ear and observe the change in the 

 apparent localization of the sound. Explain this phenomenon. 



Note the effects produced by placing the tuning-fork upon different 

 parts of the head. 



Place the tuning-fork upon the teeth. Close one ear and note the 

 apparent change in the location of the sound. 



