262 C. PFAFFMANN 



the next stimulus. Solutions were maintained at about 34°C, which was 

 neutral for the arousal of temperature sensations in our situation. We 

 found that, depending upon the subject, the threshold for detection of 

 NaCl was 100 to 1000 times lower under the continuous rinse than when the 

 tongue was bathed by saliva between stimulations. This great increase in 

 sensitivity with adaptation to distilled water suggests that salivary com- 

 ponents provide an ambient adapting background, perhaps akin to the 

 effect of general illumination on visual dark or light adaptation. These 

 results recall to mind those obtained by Hahn a number of years ago with 

 his Geschmackslupe, a flow chamber stimulator. This advice adapted the 

 tongue to distilled water or solution and restricted the stimulus to a circum- 

 scribed area. One of his subjects gave a threshold for NaCl of 52x10'^ M, 

 whereas a second gave a value of 13x10"^ m (Hahn, 1949). The extremely 

 low value of the second subject is lower than we have seen in our most 

 sensitive subject. 



Hahn showed that adaptation to different concentrations of NaCl 

 elevated the threshold for NaCl to a value just above that of the adapting 

 stimulus. Most of his stimuli were well above threshold. Accordingly, 

 McBurney examined the effect of adapting the tongue to weak salts closer 

 to threshold concentrations using 0.000069 m, 0.00069 m, and 0.015 m NaCl, 

 as well as distilled water and saliva. Figure 4 illustrates the change in 

 threshold under all these conditions for one subject. Four subjects in all 

 were employed and each showed the same effect. The figure shows the 

 concentration of adapting solution along the abscissa and concentrations of 

 threshold for detection determined by a modified ascending method of 

 limits. "Check stimuli " of pure water were introduced randomly in the 

 stimulus series and false reports to water were corrected. This maintained 

 a false alarm rate for four subjects at about 20 per cent. A fifth subject's 

 results were discarded because of an excessive false alarm rate. 



Two conditions of rinse or no rinse were obtained on any one day in a 

 partially counterbalanced manner so that 6 days of experimentation were 

 required to obtain 12 data points. The diagonal line shows the iso-equality 

 values for adapting stimuli and threshold. Threshold values greater than 

 the concentrations of the adapting concentrations fall above the diagonal 

 line. The value of the salivary sodium for each S, determined by a flame 

 photometer analysis, is plotted at the appropriate abscissa value. Each 

 point is the threshold for one daily session. 



These results indicate that the threshold is significantly altered by adap- 

 tation to water or weak saline solutions. Furthermore, the threshold 

 values obtained when the tongue is adapted to saliva closely approximates 

 the value to be expected if salivary NaCl were the primary factor influenc- 

 ing NaCl thresholds. These results emphasize the importance of giving due 

 regard to the influence of ambient salivary background. It would be 



