LESSON XXXVII 



THE SENSE ORGANS (Continued) 

 TASTE, SMELL, HEARING 



1. Structure of the Taste-buds. Study histologic preparations of 

 the taste-buds. 



2. Distribution of Taste. Place a crystal of cane-sugar upon the 

 tip of the tongue. Note that there is a definite latency caused by the 

 fact that solid substances cannot be tasted. They must first go into 

 solution. 



Place a crystal of cane-sugar upon the tip of the tongue and another 

 upon its posterior area. Where is the sweet taste most pronounced? 



Employ a solution of sulphate of quinin (bitter), a 5 per cent, solu- 

 tion of cane-sugar (sweet), a 10 per cent, solution of NaCl (saline), 

 and a 1 per cent, solution of acetic acid (sour). Apply these solutions 

 to different parts of the tongue by means of a cameFs-hair brush, and 

 observe where each is tasted most acutely. 



3. "Threshold Value" of Taste. Moisten the tongue with J tea- 

 spoonful of a 1 : 1000 solution of cane-sugar. Do you perceive a sweet 

 taste? Rinse the mouth and repeat the experiment with solutions of 

 the following strengths: 1 : 800, 1 : 600, 1 : 400, and 1 : 200. Which 

 solution produces the least perceptible sweet taste? How does the 

 acuity of taste in smokers compare with that in non-smokers? 



4. Taste Reaction of Single Papilla. By using a lens select a fungi- 

 form papilla near the tip or side of the tongue. Apply to it the tip of 

 a camel's-hair brush moistened with one of the fluids provided for this 

 purpose, viz., weak and strong solutions of cane-sugar, sodium chlorid, 

 tartaric acid, and quinin. The subject should indicate the taste which 

 he perceives. Does the papilla experimented with respond to more 

 than one of the agents used? Test other papillae in the same manner. 

 Explain. 



If a papilla be found which reacts to bitter, paint it with a solution 

 of cocain. To another, which is particularly responsive to sweet, apply 

 a saturated alcoholic solution of gymnemic acid. . Note the result in 

 each case. 



5. Electric Stimulation. Inadequate Stimuli. Connect two small 

 zinc electrodes with a series of 4 dry cells. Apply one of the electrodes 

 to the upper and the other to the lower surface of the tongue. An acid 

 taste will be obtained at the positive and an alkaline one at the negative 

 pole. The objection that electrolysis is the cause of these sensations 

 may be met by employing non-polarizable electrodes. Moreover, even 

 single shocks which cause practically no electrolysis, give rise to taste 

 sensations. 



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