LESSON XXI. TASTE AND SMELL. 



See Note under Touch, p. 100. 



1. Rough determination of threshold for the tip 

 of the tongue. Take the following aqueous solutions, 

 label each set 1, 2, 3, 4, 5; No. 1 being the strongest 

 solution. 



Cane sugar, 6, 3, 1-5, -75, and -375 p. c. 



Sodium chloride as cane sugar. 



Fuming sulphuric acid, 1, -5, -25, -05, -01 p.c. 



Sulphate of quinine, -2, -1, -02, -004, -0008 p.c. 



Have ready small pipettes of equal size, one for each 

 set of solutions (the pipette must be washed out with 

 water if it is used for a weak solution after a strong one) ; 

 a dish of water to clean out the pipettes ; an additional 

 pipette with pure water ; a tumbler of water to rinse out 

 the mouth. 



B lets fall a drop of one of the weaker solutions (No. 4) 

 or of water on the tip of A's tongue; after 5 seconds A 

 says what he thinks it is, and this is noted by B. A takes 

 ' a mouthful of water and ejects it, preventing the test 

 substance so far as possible from coming into contact 

 with the back of the tongue and soft palate. 



This procedure is repeated till all the No. 4 solutions 

 and water have been tested. 



Then No. 3 solutions and water are similarly tasted; 

 and so on. When it is clear that a solution is distinctly 

 tasted, no stronger solution of that substance should be 

 applied. It will probably be found that a strong solution 



