134 SMELL, TASTE, ALLIED SENSES 



3. Qualities of Taste. Tastes, unlike odors, fall into 

 a limited number of well-circumscribed groups, which 

 have received distinctive names such as sour, saline, bit- 

 ter, sweet, and the like. The multitude of flavors and 

 other sensations associated with our food are undoubt- 

 edly mixed in character and include touch, heat, cold, the 

 common chemical sensation, and especially odor. By ap- 

 plying materials in weak solution, at the temperature of 

 the mouth and with the nostrils closed, extraneous sen- 

 sations may be eliminated and there remains a certain 

 irreducible residue, the tastes. Zenneck (1839), Valentin 

 (1848), Duval (1872) and later Steinberg (1898) admit- 

 ted only two classes of tastes, sweet and bitter. Stich 

 (1857), however, long ago showed that sour was a sensa- 

 tion produced by stimulating only a limited part of the 

 buccal surface, and Schiif (1867) made the important 

 observation that a solution of acid too weak to stimulate 

 the general mucous surface would nevertheless call forth 

 a sour sensation when it was applied to the gustatory 

 region. Von Vintschgau (1880) made similar observa- 

 tions concerning the saline taste; solutions of sodium 

 chloride, potassium iodide, and ammonium chloride, if 

 sufficiently weak, will stimulate the organs of taste, but 

 if strong they will stimulate not only these organs but 

 the nerve endings of the general buccal cavity also. In 

 consequence of such observations sour and saline are now 

 universally included with bitter and sweet as true tastes. 



In addition to these four tastes there are a number 

 of questionable ones such as metallic and alkaline, tastes 

 that were originally accepted by Wundt (1887) among 

 others. The so-called metallic taste is excited by solu- 

 tions of salts of the heavy metals, silver, mercury, and 



