KINDS OP TASTE SENSATIONS 447 



sidered as the specialized end organs of the sensory taste 

 nerve fibers. 



The perception of taste is produced by the connection 

 of these fibers and the brain through the fifth and ninth 

 pairs of cranial nerves. 



Stimulation and sensitiveness. — These taste buds can 

 be stimulated only by substances in solution, and in dis- 

 solving solids the saliva of the mouth plays an important 

 part in the production of taste sensations. Dry salt or 

 sugar placed upon the tongue remains tasteless until 

 dissolved by the saliva. The sensitiveness of the taste 

 buds to stimuli is influenced by many external factors as 

 well as by the concentration and character of the dis- 

 solved substance. The result of experiments in this 

 direction may be summarized as follows: 



Summary. — (a) The taste buds are most sensitive at a tem- 

 perature of from 50 to 86° Fahrenheit. Very high or very low- 

 temperatures tend to paralyse the taste buds and thus lessen or 

 destroy the sensation of taste. 



(6) Rubbing the substance to be tasted against the tongue 

 increases the sensitiveness of the taste buds. This accounts for 

 our habit of rubbing the tasted food against the walls of the mouth 

 with the tongue. 



(c) The sensitiveness varies with the character of the tasted 

 substance. The order of greater sensitiveness in this respect 

 being bitterness, sourness, sweetness, saltness. 



Kinds of taste sensations. — While our taste sensations appear 

 to be very varied in Icind, it has been demonstrated that they are 

 actually only four in number, namely, bitter, acid, sweet, and 

 salt. The bitter taste is most developed at the back of the tongue, 

 the sweet taste at the tip of the tongue, the acid or sour taste 

 at the sides, and the salt taste is nearly equally distributed. 

 Many of our taste sensations are combinations of these four pri- 

 mary sensations with odor or sight sensations This fact can be 



