152 PHYSIOLOGY CHAP. 



and the cutaneous sensations later, he employed it to discriminate 

 the tactile qualities of sapid substances, and thus proved that 

 acid and salt are true gustatory sensations. 



Edge worth discovered that the masticated leaves of Gymnena 

 silvestre have the property of completely abolishing the taste for 

 sweetness. Hooper (1887) observed more accurately that sensa- 

 tions of sweet and bitter were entirely removed by gyrnnenic acid. 

 Shore found the action of this acid to be most intense for sweet, 

 less for bitter, still less for salt, and nil for acid. Kiesow con- 

 firmed these results, but found weak action even on the acid taste. 

 He concluded that the action of cocaine is more extensive than 

 that of gymnenic acid, and that the latter acts on sweet almost as 

 cocaine upon bitter. According to Kiesow, gymnenic acid has no 

 effect upon the tactile, thermal, and pain sensibility of the tongue. 



Fontana (1902), under Kiesow's direction, found that eucaine-J5 

 has a similar action on taste to cocaine, i.e. predominantly upon 

 bitter. 



Ponzo found that stovaine at a certain concentration abolishes 

 the sensations of sweetness and bitterness, while it is still possible 

 to perceive salt and acid, though faintly. He also found that 

 the period of anaesthesia is succeeded by a period of hyperaesthesia 

 which is limited to certain gustatory sensations, and which he 

 holds to be of central origin. Stovaine produces this hypergeusia 

 for salt tastes ; cocaine for sweet and bitter. 



Herlitzka observed that Voth normal solution of chromium 

 nitrate produces hypoaesthesia for sweet and salt, and in a less 

 degree for bitter; also that cobalt chloride causes gustatory par- 

 aesthesia for a period of 24 hours, during which all fluids taste 

 salt. 



Artificial changes of the normal mean temperature of the 

 tongue, again, may depress or temporarily inhibit the excitability 

 of the peripheral organs of taste. Weber first noted that on 

 plunging the tongue for 30 to 60 minutes in water at 40 to 42 R, 

 or into iced water for the same time, the sweetness of sugar was 

 no longer perceptible. This observation was confirmed by Guyot, 

 Aducco and U. Mosso, and Kiesow. Kiesow found that 10 

 minutes' action of iced water or warming to 40-51 C. sufficed to 

 make the tongue insensitive not only to sweet but also to other 

 strong tastes, with the exception of acid, which could still be 

 perceived under these conditions. 



The temperature of the solutions employed as taste stimuli, 

 again, affects the threshold of gustatory sensibility. According to 

 Camerer (1880) the optimum of the stimulus is between 10 and 

 20 C. Taste sensibility, on the contrary, according to Kiesow, 

 does not alter within the limits of temperature at which the 

 solutions employed do not arouse decided sensations of heat or cold. 

 Above and below these limits gustatory sensibility diminishes. 



