108 ELEMENTARY PHYSIOLOGY. XXI. 



of the tongue. When the anode is on the back of the 

 tongue an acid taste with some bitter will be set up 

 there; when the cathode is applied to the back of the 

 tongue the taste will be alkaline with some bitter. On 

 applying the electrodes elsewhere, probably the acid and 

 alkaline sensation will alone be felt. 



7. Lightly press the point of a needle on the tongue, and note 

 approximately the degree of pressure at which touch passes into 

 pain. Then apply to the tip with a camel-hair brush a 1 p.c. solution 

 of cocaine, repeating if necessary. At a certain stage touch will still 

 be felt, but not pain. 



8. Appty an extract of gymnema with a camel-hair 

 brush to the back of the tongue (10 grams of the leaves 

 of Gymnema silvestris pounded, boiled for 5 minutes in 

 water and filtered) ; leave for about 30 sees. ; wash out 

 the mouth; test the taste sensations with the stronger 

 solutions; the acid and salt will still be tasted, but not 

 quinine or sugar. The solutions must of course not over- 

 pass the regions to which gymnema has been applied. 



9. Threshold for smell. Prepare standard solutions 

 of camphor thus : dissolve 1 gram of camphor in strong 

 spirit, dilute with water to 200 c.c. Put a little of this 

 solution into a test-tube and label (1). Take 1 c.c. of (1) 

 and add 4 c.c. of water, label this (2). Take 1 c.c. of this, 

 add 4 c.c. of water and label (3), and so on till 9 solu- 

 tions are obtained. Label 10 a test-tube containing 

 water only. 



B takes water only and the weakest solution of cam- 

 phor, and gives first one, then the other, to A to smell, 

 and records the answer. Then similarly with the solu- 

 tion next stronger in the series, and so on but not using 

 any solution stronger than that which is said to be 



