142 PHYSIOLOGY CHAP. 



of acid or salt applied to the tongue produce specific sensations 

 which are not aroused from any other sensory surface, and which 

 give particular information about these substances under the 

 familiar name of acid or salt taste." This amounts to saying that 

 acid and salt are true tastes, although, unlike sweet and bitter, 

 they may be associated with general sensations when not 

 sufficiently diluted. 



Bain, Wundt, and others admit the alkaline and metallic also 

 among the true tastes. It was long debated whether these two 

 tastes should be admitted among the four generally recognised as 

 primitive, or whether they should be considered as compound 

 sensations due to the admixture of several tastes. Von Vintschgau 

 recognised that the metallic taste excited by electrical stimulation 

 of the tongue is very difficult to analyse, and that in alkaline and 

 astringent tastes common sensibility plays such an important part 

 that it is hard to know if the taste organs also are excited. 

 Oehrwall holds that the alkaline taste results from the combina- 

 tion of many tastes, associated with sensations of contact. The 

 researches of Kiesow and Hb'ber led these authors also to the con- 

 clusion that the alkaline and metallic tastes depend on the associa- 

 tion of several primitive gustatory sensations; that acid and 

 sweet are components in a metallic taste ; and that in an alkaline 

 the general sensibility components are associated sometimes with 

 bitter, sometimes with sweet. 



Von Frey assumed that alkaline and metallic tastes are mixed 

 sensations with an olfactory component. Herlitzka showed that 

 the so-called metallic taste is neither a gustatory nor a mixed 

 sensation, but purely olfactory. More recently v. Frey came to 

 the same conclusion in regard to the alkaline taste. 



Henle distinguished as insipid tastes the impressions produced 

 by solutions that are poorer in salt than the saliva. The taste 

 organs are so accustomed to the action of the buccal secretions that 

 the latter are quite indifferent, as regards taste. But directly the 

 concentration of these fluids is lowered, we become aware of a faint 

 or indefinite sensation commonly known as insipid. A typical 

 illustration of this is the sensation produced by distilled water, 

 which is deprived of carbonic acid. According to Kiesow, a very 

 dilute alkali also has an insipid taste, and a much diluted mixture 

 of salt and sugar is insipid. 



In conclusion, the usually recognised qualities of taste are 

 reduced to four : sweet, bitter, acid, salt. These are primitive or 

 elementary tastes, because they cannot be further analysed. If 

 we make of substances belonging to each of these four groups 

 solutions that will arouse equal sensations, we cannot distinguish 

 between the sensations aroused, e.g. by hydrochloric, nitric, 

 sulphuric, acetic, and oxalic acid. The same applies to the 

 bitter substances, e.g. strychnine, quinine, digitaline, morphine, 





