SKIN SENSATIONS 197 



TASTE. 



Closely allied to the skin sensations are those of taste and smell. 

 The following experiments on taste are important. 

 Experiment 92. (a) Dry the tongue and apply a crystal of salt 



or sugar. Note that it is not tasted. 



(b) On the dry surface of the tongue apply by means of a 

 camel's hair brush a solution of quinine (1 to 1,000), sodium 

 chloride (1 to 200), cane sugar (1 to 50), and sulphuric acid 

 (1 to 1,000). Determine at which part of the tongue the strong- 

 est sensation is produced by each. 



(c) Prepare a series of solutions of gradually increasing 

 strengths of quinine, salt, sugar, and sulphuric acid, beginning 

 in each case at 1 in 5,000, and apply to that portion of the tongue 

 most sensitive to the respective substances. Determine what 

 strength of solution is necessary to stimulate taste. 



(d) Apply with a brush a little of the sugar solution of the 

 strength which just stimulated taste, and follow with a drop of 

 salt solution of the same taste value. Note that the salt neu- 

 tralizes the effect of the sugar and neither is tasted. 



(e) Take a solution of strong salt water into the mouth and 

 wash out with distilled water. Note that the water tastes 

 sweet (negative after-stimulation). 



PRESSURE. 



Experiment 93. Weber's Law. With the hand outstretched on 

 the table and palm upward, the subject being blindfolded, a 

 piece of cardboard 4 cm. square is placed on the finger tips. 



With 5 gms. as the standard determine the least increment 

 necessary to detect a difference. In all of these observations 

 no muscualr effort must be made; moreover the weights must 

 be applied as gently as possible. 



Determine the increments necessary for the following 

 standards: 10 gm., 50 gm., 100 gm., 200 gm., 1,000 gm. 

 Pressure and Muscular Sense. Repeat the above observa- 

 tions with the hand removed from the table, the muscles of the 

 hand and arm being used to their utmost in determining the 

 threshold of difference. 



