LXXVI.] TOUCH, SMELL, TASTE, HEARING. 371 



a 5 per cent, solution of sugar (street), a 10 per cent, solution of 

 common salt (saline), and a i per cent, solution of acetic acid 

 (acid). 



(a.) Wipe the tongue dry, lay on its tip a crystal of sugar. It 

 is not tasted until it is dissolved. 



(b.) Apply a crystal of sugar to the tip and another to the back 

 of the tongue. The sweet taste is more pronounced at the tip. 



(e.) Repeat the process with sulphate of quinine in solution. It 

 is scarcely tasted on the tip, but is tasted immediately on the back 

 part of the tongue. 



(d.) Test where salines and acids are tasted most acutely. 



(e.} Connect two zinc terminals with a large Grove's battery, apply them to 

 the upper and under surface of the tongue, and pass a constant current through 

 the tongue. An acid taste will be felt at the positive, and an alkaline one at 

 the negative pole. 



(/. ) Close the nostrils, shut the eyes, and attempt to distinguish by taste 

 alone between an apple and a potato. 



(g.) ftymnema Sylvestre. Use a 5 p.c. decoction of the leaves and apply 

 it to limited areas of the tongue by means of a camel-hair pencil. In 20-30 

 seconds wash out the mouth and then test the action of glycerin (5-10 p.c.), 

 quinine (i p.c. with .01 p.c. of HJ30 4 ), H. 2 S0 4 (.05 p.c.), NaCl (.5 p.c.). 



The sweet and bitter tastes are readily prevented in all regions ; but acid 

 and saline tastes are not influenced (L. E. Shore, " A Contribution to our 

 Knowledge of Taste Sensations," Jo urn. of Phys., xiii. p. 191). It has no effect 

 on tactile sensations. 



11. Ear. Hearing. 



(a.) Hold a ticking watch between your teeth, or touch the 

 upper incisors with a vibrating tuning-fork, close both ears, and 

 observe that the ticking is heard louder. Unstop one ear, and 

 observe that the ticking is heard loudest in the stopped ear. 



(b.) Hold a vibrating tuning-fork on the incisor teeth until you 

 cannot hear it sounding. Close one or both ears and you will hear 

 it. 



(c.) Listen to a ticking watch or a timing-fork kept vibrating 

 electrically. Close the mouth and nostrils, and take either a deep 

 inspiration or deep expiration so as to alter the tension of the air 

 in the tympanum ; in both cases the sound is diminished. 



(d.) Connect two telephones in circuit with a vibrating Neef's 

 hammer of an induction machine, and place a telephone to each 

 ear ; one hears the sound as if it came from within one's own head 

 in the vertical median plane. 



(e.) With a blindfolded person test his sense of the direction of 

 sound, e.g., by clicking two coins together. It is very imperfect. 

 Let a person press both auricles against the side of the head, and 

 hold both hands vertically in front of each meatus. On a person 



