THE SENSE OF TASTE 



relatively uninfluenced (191). Such observations led 

 to the view that taste consisted of four different 

 modalities, salt, sour, bitter and sweet, each with its 

 particular type of receptor even though no obvious 

 histological diflferences distinguished taste buds from 

 different regions of the tongue (147). 



Electrophysiological studies show that the chorda 

 tympani nerve discharge elicited by taste solutions 

 on the tongue, varies with concentration above the 

 threshold. In figure 4 the basic taste stimuli can be 

 ranked in order of effectiveness: quinine, hydro- 

 chloric acid, sodium chloride, potassium chloride and 



400. 



300 _ 



ZOO. 



3 -2 



LOG MOLAR CONG 



FIG. 4. Height of integrator deflections to stimuli of differ- 

 ent concentrations in one cat preparation. Ordinate gives de- 

 flections in arbitrary units. [From Pfaffmann (164).] 



sucrose but the exact order or magnitude of response 

 \aries with species. In rodents (rat, guinea pig and 

 hamster) sodium chloride is more effective than 

 potassium chloride, whereas in carnivores (raccoon, 

 cat and dog) the converse is true. There is very little 

 response to sugar in the cat, somewhat more in the 

 rat and still more in the hamster and guinea pig. The 

 quinine response is better in the cat than in the rat 

 or rabbit (21, 163). 



A typical single fiber discharge from the rat chorda 

 tympani is shown in figure 5 (164). The threshold 

 varies from unit to unit so that as concentration in- 

 creases there is an increase both in the number of 

 units active and in the frequency of discharge. The 

 fiber in figure 5 also responded to hydrochloric acid 

 and potassium chloride. A wider sample of the 'spec- 

 trum' of sensibilities of different fibers in the rat 

 chorda tympani is shown in figure 6. The pattern of 

 sensitivity varies from fiber to fiber. Although some 

 elements (.4 and fi) are relatively specific, others 

 (especially /) have a broader sensitivity. These dif- 

 ferent sensitivities cannot be readily grouped into the 

 basic four types of classical theory. Studies (121) in 

 which micropipettes have been inserted into the 

 individual cells of the taste bud show the same kind 

 of sensitivity pattern in the receptor cells thernseh-es. 

 This important observation disposes of the possi- 

 bility that the overlapping sensitivities of single fibers 

 of the chorda tympani result from the branching of 

 fibers and termination upon more than one type o 



1.0 



-liiM—L 



• r»>-ii'iiM> n I'lr^i'iiO ' i~ Wi 1J._. _i,».|iii 



■C'^»»<^ 



rJiiiiiiL.liilJl.l..Jl.J,.>i 



ni^^f^^^Wv* 



J,,.L.i.i,, I ...UlLiLL L. 



iir Q ii - If ^ il l U ilil J.L [1 l iii ■■ | J--1- ^ J , \ ^ --i I -I' ll * ' | -1 | - | ■ -I - I - -\ i .'~\ \ 



.03 



^^"^^^■^^^W^ri^iiJ^ LJ*^^— V ■^^^'W' U ^^ ^ 



*pJ-i ^.LLLL l'y*.»*>* ^u.^^ L .1 ■ ■' / 





l^i^«i tft^^if^t^ ^i.>^i y »>^>»>iOx^^»J>vt^|^»W>i>^>«iX^ 



.01 



.003 



4«M^^B«i^i»4irflMM 



MMMtavNwl^«Mb«N 



.001 



inpi|i->^ii i<liiU>> 



HzO 



RAT No CI Series 



I I 



.1 sec. 



FIG. 5. Response of a single element from the rat sensitive to NaCl. This element also responds 

 to HCl and KCl. Responses to quinine and sucrose were insignificant. [From Pfaffmann (164).] 



