XVIII 



THE SPECIAL SENSES AND SENSATIONS 



257 



Taste guides us in the selection of foods and gives 

 an added pleasure to eating. It may be highly culti- 

 vated by constant practice, as is shown in expert tea 

 tasters and French epicures. 



1 . Rub your hand over a cat's tongue and notice how rough it 

 feels. Compare with a cow's tongue. 



2. Put a drop of vinegar on the back, on the tip, and on the 

 sides of the tongue. Which is most sensitive ? 



3. In the same way try a bit of sugar, a little salt, and some 

 quinine. 



4. What do you learn from exercises 2 and 3 ? Explain. 



175. The Sense of Smell. The mucous membrane 

 of the nasal cavities contains the sensitive ends of the 

 nerves of smell. 

 They are most 

 numerous in the 

 upper half of the 

 nasal cavities, and 

 are quite removed 

 from the direct 

 current of air that 

 constantly passes 

 through the nose 

 in breathing. That 



is why we " sniff 

 and smell " to de- 

 tect a faint odor. 



Any substance 

 that can excite the nerve of smell gives off to the air 

 very fine particles, called effluvia. The particles dissolve 



FlG. 136. The outer wall of the left nasal cav- 

 ity. /, the nerve of smell and its branches; 

 V, V, cranial nerve; ST, MT, and IT, tur- 

 binate bones; and Pa, hard palate. (From 

 Huxley.) 



