264 



Physiology. 



Solution Necessary for Tasting. Substances must be 

 dissolved before they can be tasted. If the tongue be 

 wiped dry, and a few grains of salt or sugar be placed on 

 it, the taste will not be perceived for a little time. Insol. 

 uble substances give no taste. 



Flavors. What we call flavors affect us more through the sense of 

 smell than through taste. If the nose be held shut, a piece of onion 

 placed on the tongue does not produce what we usually call the taste 

 of the onion. By holding the nose we may get rid of the disagreeable 

 part of taking certain medicines. Let the pupil experiment with various 

 substances as above indicated. 



The Sense of Smell. The nerves of smell, the olfactory 

 nerves, are distributed in the walls of the nasal passages. 

 The sense of 

 odor gives us 

 information as 

 to the quality 

 of food and 

 drink, and more 

 especially as to 

 the quality of 

 the air we breathe. 

 we find the organ 



Olfactory Bulb 



Olfactory Nerves. 



Branches of 

 Fifth Nerve' 



Turbinated 



Hence 

 placed 



at the opening of the 

 respiratory passages, and 

 close to the organ of 

 taste. 



Fig. 102. 



Nerves of the Outer Wall of the 

 Nasal Cavity. 



Why we Sniff. In cfuiet breathing the air passes along the lower 

 air passages just above the hard palate. When we wish to test the 

 quality of the air, we sniff, that is, make a sudden inspiration by jerking 

 the diaphragm down, and air from the outside then rushes into the 

 upper nasal passages, over the walls of which the olfactory nerves are 

 spread in the mucous memDrane. In inflammation, as from a cold^ 

 the narrow nasal passages, especially the upper, are often closed. 



