KAHLENBERG — ACTION OF SOLUTIONS ON TASTE. 29 



with the protoplasm of the nerve, they would probably not re- 

 act with it sufficiently to produce sensations of taste. 



Retrospect. 



One may briefly summarize the salient points contained in 

 the foregoing as follows: — 



1. In order that a substance may affect the sense of taste, 

 it must be soluble in water; it must be readily diffusible; and 

 it must be capable of reacting chemically with the protoplasm 

 of the terminals of the nerves of taste. 



2. The modern theories of solutions lead to the conclusion 

 that the taste of a solution that conducts electricity ought in 

 general to be that of the ions and the undissociated molecules 

 that the solution contains; furthermore, the taste of a solution 

 in which ionization is practically complete should be simply that 

 of the ions. This is supported by the results of the investiga- 

 tion of the taste of solutions of electrolytes above given. 



3. Sour taste is caused by hydrogen ions. The sense of taste 

 is able to detect hydrogen ions even in -^ solutions. In more 

 dilute solutions than •£$, hydrogen ions may cause simply an 

 astringent sensation. The sour taste of acetic acid solutions has 

 been found to be more intense than it ought to be according to 

 the degree of dissociation of the substance. !No explanation of 

 this phenomenon has thus far been attempted. 



4. Hydroxyl ions produce an alkaline taste, which can be 

 perceived even in -$%■ solutions. In strong solutions their 

 taste is exceedingly disagreeable. Pure water, being very 

 slightly dissociated, is tasteless probably because its undissociat- 

 ed molecules do not act on the protoplasm cf the nerve. 



5. Chlorine ions have a salty taste. The taste of common 

 salt solutions is mainly that of chlorine ions. Chlorine ions 

 can still be faintly tasted in -^- solutions. Bromine ions also 

 have a salty taste, which, however, is slightly different in qual- 

 ity from that of chlorine ions. The sense of taste appears to 

 be able to detect chlorine ions at a slightly greater dilution than 

 bromine ions. The ions C10 3 and Br0 3 have a somewhat similar 



