58 A COURSE ON ZOOLOGY. 



usually consisting of various sulphides and salts of 

 iron. 



Taste. The sense of taste gives us notions of savors. 

 Its principal organ is the tongue, whose upper surface is 

 covered with papillaB that are similar to the papillae of 

 touch, and are called gustatory papillae. They receive 

 nerve-filaments coming principally from the glosso- 

 pharyngeal nerve. These papillae are shaped like mush- 

 rooms (fungiform), or like the calyces of flowers (calci- 

 form), and the latter form seems to be the kind particu- 

 larly serving as organs of taste. The calciform papillae 

 may be seen regularly distributed on the posterior upper 

 surface of the tongue, where their grouping forms a letter 

 Y, called the lingual V. 



Not all substances are tastable : thus a piece of glass 

 produces on the tongue only an impression of touch. 

 In order that a substance may be tasted it must either 

 be liquid or capable of being dissolved by the saliva. 

 This fact explains why the taste becomes dulled when 

 the mouth and tongue are dry. The causes of the 

 diiference in tastes are unknown. Frequently Certain 

 impressions are considered as tastes that depend much 

 more directly on the sense of smell. 



Smell. The sense of smell, which gives us notions of 

 odors, is located in the nasal fossae. 



The direct cause of odorous impressions is the contact 

 with our olfactory organs of minute particles of the 

 odorous substance in the form of gas or vapor. As the 

 air we breathe passes continually over the parts in whicK 

 the sense of smell resides, it is impossible that an odor 

 should exist around us without our noticing it almost 

 immediately. 



The nasal fossae form a double cavity above the roof 



