156 SMELL, TASTE, ALLIED SENSES 



substances are known whose solutions so affect the tongue 

 that its powers of taste become temporarily changed. 

 Thus these substances give rise to what have been called 

 after-tastes. In almost every instance the taste that 

 suffers change is the sweet taste and this is increased in 

 efficiency. Thus Aducco and Mosso (1886) found that 

 after the tongue had been held in dilute sulphuric acid 

 for five to ten minutes, distilled water was then capable 

 of exciting a very sweet taste. A solution of quinine was 

 also sweet to the taste at the tip of the tongue, but it 

 remained normally bitter at the base. This change was 

 not brought about by other acids such as acetic, citric, and 

 formic. Frentzel (1896) also noticed that after washing 

 out the mouth with a weak solution of copper sulphate, 

 smoking a cigar was accompanied by a sweet taste. Ac- 

 cording to Zuntz (1892) a solution of sodium chloride of 

 one per cent strength will increase the sweetness of sugar, " 

 an observation confirmed by Heymans (1899). A mouth 

 wash of potassium chlorate is well known to leave the 

 tongue so that distilled water tastes sweet (Nagel, 1896). 

 In all these instances it is probable that the constitution 

 of the receptor for the sweet taste is so changed by the 

 first solution applied to it that it becomes hypersensitive 

 to its normal stimuli such as sugar or even open to novel 

 stimuli such as distilled water. 



Complete loss of taste or ageusia is known to accom- 

 pany hysterical and other abnormal nervous states. It 

 may be temporary or, in the case of certain lesions, per- 

 manent in character. 



14. Gustatory Contrasts. Although some acids in- 

 crease the sensitiveness of the sweet taste and thus give 

 ground for a gustatory contrast, it is questionable whether 



