296 STUDIES IN PHYSIOLOGY 



my nose, and then put into my mouth successively a piece 

 of potato, a piece of apple, and a piece of onion, I am unable 

 to distinguish one from another. In other words, we learn 

 that many of our foods are not tasted, but smelled. The 

 same fact is demonstrated by an experience with a head 

 cold, when the mucous membrane of the throat and nose 

 cavities is so inflamed that the odorous particles do not 

 affect the sense organs of smell; we then lose the power 

 of "tasting" our food. 



In reality, we can taste but four different classes of sub- 

 stances, namely, sweet, sour, bitter, and salt. All the vari- 

 ous " flavors " of foods and drinks are therefore distinguished 

 by smell, and not by taste. By the help of the taste buds 

 alone we cannot even distinguish the sour of vinegar from 

 that of hydrochloric acid. Before we can taste any sub- 

 stance, however, it must be made into a solution, otherwise 

 the sensory hairs of the taste buds are not affected. This 

 is the reason why sand and other insoluble substances are 

 tasteless. 



4. THE SENSE OF SMELL 



The Nasal Cavities. The two nose cavities are separated 

 by a central partition composed partly of bone and partly 

 of cartilage. These cavities communicate with the outside 

 air by the two external nostrils, and at the back they open 

 by the internal nostrils into the throat cavity. Each nasal 

 cavity is separated from the cavity of the mouth by the hard 

 palate, and from the brain by a portion of the ethmoid bone. 

 In the latter are numerous perforations through which pass 

 the branches of the first pair of olfactory nerves. Hence 

 this roof of the nasal cavities is known as the crib'i-form 

 plate (Latin cribrum = a sieve). Projecting from the outer 

 wall of each nasal cavity, as we learned in studying the 

 skeleton, are three thin bones, each rolled more or less like 

 a scroll ; they are the superior, middle, and inferior spongy 

 or turbinate bones. 



