TASTE AND SMELL 107 



of cane sugar must be applied before it is tasted ; a rather 

 less strong solution of salt ; a still less strong solution of 

 acid ; whilst a relatively weak solution of quinine will be 

 effective. 



2. Comparison of sensitiveness to bitter sub- 

 stances of the tip and of the back of the tongue. 



Take the solution next below that which gives a bitter 

 taste on the tongue. Put two drops on the tip of the 

 tongue and rub the tip against the lip ; as soon as it is 

 clear that it is not tasted put two drops on the back 

 of the tongue and press the back of the tongue against 

 the soft palate. It will usually be tasted at once. 



3. Determine roughly in the manner given in 1 the threshold 

 for the various substances when placed on the back of the tongue. 

 In these experiments care should be taken, so far as possible, to 

 rinse out the mouth without pressing the back of the tongue against 

 the roof. 



4. Take a few c.c. of the solution of sugar next below 

 that which is tasted on the tip of the tongue, and roll it 

 about in the mouth, it will taste sweet. This is largely 

 due to a greater area being stimulated, and perhaps also 

 to some part of the mucous membrane being more sen- 

 sitive to sweet than the tip of the tongue. 



5. Take any of the No. 1 solutions, and place a drop 

 upon the middle of the upper surface of the tongue, it 

 will not be tasted, provided it does not spread to other 

 regions. 



6. Arrange for a constant current with two Daniell's 

 cells. Apply one electrode to the middle region of the 

 upper part of the tongue, the other electrode to the back 



