THE SENSE OF TASTE 523 



activity. Other sense organs appear to show the same 

 polarity relations, e.g. the tactile receptors of the 

 frog skin and photo receptors of the Limulus eye, 

 suggesting that these effects are not specific to taste 

 (138, 139). These effects are just opposite to those 

 seen in the axon where anodal block and cathodal 

 excitation are found. 



Studies of alternating current stimulation support 

 the view that the receptor ceil mediates the electric 

 taste at low frequencies from 30 to 50 cps at which 

 sour predominates. The low frequencies presumably 

 can stimulate the receptor organs with their slower 

 time constants. High frequencies around 1000 cps 

 elicit a more complex bitter taste. The high fre- 

 quencies may stimulate ti.ssues with faster time con- 

 stants, i.e. the nerve fibers themselves (41). 



Intermittent square wave stimulation has been 

 employed in studies of the so-called 'flicker fusion' of 

 taste. The original studies (6) purporting to demon- 

 strate gustatory flicker fusion at frequencies between 

 125 and 350 cps have not been confirmed Cii3> i 70j 

 183), although it is true that something akin to fusion 

 can be reported. The effect appears to be largely a 

 tactual phenomenon which can be demonstrated in 

 regions of the mouth and lips where no taste buds are 

 found (170). Reports of true taste fusion (38) occur 

 with extremely low frequencies in the range of from 

 0.3 to 10 cps. 



Parameters of Slimiilaliori 



TEMPERATURE. The rate of most chemical reactions 

 is increased by a rise in temperature. Early work 

 showed that taste was optimal in a middle range 

 variously reported between 10° and 20°C, 20° and 

 30°C and 30° and 40 °C. At the extremes of 0° or 

 50 °C the tongue is nearly insensitive especially after 

 it has been immersed in solution (198). Komuro 

 (125) studied intermediate values and reported a 

 drop in threshold with temperature rise from 10° to 

 30°C, with some suggestion of an increase beyond 

 30 °C for all stimuli. Chinaglia (46) found no change 

 in threshold but did find a change in reaction time. 

 The interpretation of reaction time data is somewhat 

 equivocal because, in another study (143), no corre- 

 lation was found between reaction time and thresh- 

 old for sodium chloride over a wide temperature 

 range. 



Goudrian (86) showed that the apparent taste 

 intensity of sugar solutions increased with increasing 

 temperature between 10° and 40°C. Acid showed a 



FIG. 14. The effect of temperature on taste thresholds for 

 sodium chloride, quinine sulphate, dulcin and hydrochloric acid. 

 The ordinate gives the thresholds in arbitrary units. The value 

 of one unit on the ordinate differs for each of the four sub- 

 stances, as shown by the key in the figure. For example, one 

 unit for NaCI equals 0.0005 P^'' cent. [From Hahn (93).] 



similar but not as regular or as striking a change. 

 Salt and quinine fell in intensity with an optimum for 

 salt at io°C. The optimum for quinine was less con- 

 sistent. 



One of the better controlled studies is that of Hahn 

 & Gunther (gi) on absolute thresholds at different 

 temperatures using the 'Geschmackslupe.' This device 

 restricts the flow of solution to a specified region of 

 the tongue so that a preadapting flow of water at the 

 same temperature can be employed (see fig. 14). 

 Sugar sensitivity increases, salt and quinine decrease 

 and acid is unaffected by temperature rise. The 

 greatest deviations occurred with different sweet 

 stimuli. Glycol showed little change with tempera- 

 ture whereas beryllium salts and other sugars followed 

 the sucrose curve. Certain acids showed slight up- 

 turn at either temperature extreme and different 

 salts showed a flattening out or even a fall beyond 

 37°C. With different bitter stimuli there was only an 

 increase in slope. Hahn & Gunther's values do not 

 include the extremes which cause insensitivity. If 

 extended, their curves would probably have shown 

 a rise in threshold at the low and high values. 



