

SMELL. 153 



What is after-taste? 



After an aromatic substance has been tasted there remains in the 

 mouth an impression of that flavor, and if such substances be taken 

 in rapid succession, the appreciation of their flavor is lost. This 

 impression, which is left by a strong flavor, is called the after-taste, 

 and is utilized sometimes to cover the taste of a disagreeable medi- 

 cine, a strongly-flavored aromatic preceding it. 



What influence upon taste has the muscular action of the 



tongue ? 



Twofold. It breaks the food up more thoroughly by its pressure 

 against the walls of the mouth, and so brings it into a better con- 

 dition to reach the nerve-endings ; and it carries the food about the 

 mouth, so that the taste-organs are able to reach it readily. 



SMELL. 

 What are the conditions necessary to the sense of smell? 



The special organs for this sense for the reception, conduction, 

 and perception of the stimulus, as in the case of any of the senses, 

 must be in their proper condition, and a stimulus (an odor) must 

 be present to excite them. 



What are odors ? 



They are caused either by minute particles of solid matter or by 

 gases which are in the atmosphere, and they must be capable of 

 solution in the mucus of the Schneiderian membrane. The sub- 

 stance must pass in a current of air through the nostrils or it is not 

 perceived as an odor. This is accomplished by " sniffing " the air, 

 and thus creating an intermitting current which is tested by the 

 olfactory sense. In this way a trace of a gas or impalpable powder 

 may be detected which cannot be traced by chemical or other means. 

 If the substance be applied as a solution, it is not detected ; thus, 

 rose-water in a nasal douche is not noticed while the nostrils are 

 full of fluid, and' yet as soon as the nostrils are free the odor 

 appears. 



Where is the organ oT the sense of smell ? 



In the mucous membrane of the upper part of the nasal cavity. 

 The olfactory nerves are the functional nerves of the sense, and are 

 spread out in a fine network (Fig. 42) over the surface of the supe- 

 rior or turbinated bone and upper portion of the middle turbinated 

 bone, and on the upper third of the septum. The nerves end in 



