1 2 4 2 THE SENSE OF TASTE. 



when applied to the tongue destroys both sensibility to touch and to 

 taste, 1 and it is also said to destroy the sense of temperature. 2 It appears 

 that this drug destroys the power of tasting bitter substances most 

 readily, 3 and does not affect the power of tasting sweet, salt, and sour sub- 

 stances to the same degree. It also abolishes tastes electrically produced. 

 A decoction of the leaves of Gymnema sylvestre, according to most 

 observers, paralyses the sense of bitter and of sweet, 4 while others 

 maintain that all tastes are affected, though bitter and sweet tastes more 

 especially. Gymnema abolishes the bitter tastes that can be electrically 

 produced. 



Modality and quality. —Some observers maintain with Ohrwall 

 that the difference between the sensations of bitter, sweet, etc., are 

 differences not of quality but of modality. Eeferring to the definition 

 of the term, as given by Helmholtz, its introducer, 5 we find that modality 

 is that difference which exists between the sensations of different sense- 

 organs, such as, say, sweetness, warmth, and colour. We can neither 

 compare with each other sensations which differ in modality, nor do 

 they pass into each other by intermediate stages, as do sensations which 

 are associated with the same sense-organ and which differ from each 

 other in quality. We cannot say that a sweet taste is more like blue 

 than red ; here is an instance of modality. Orange is, on the other 

 hand, more like yellow than blue, and can pass into yellow by intermediate 

 sensations ; here is then an instance of quality. Accepting this defini- 

 tion of Helmholtz, it is difficult to understand how the difference 

 between, say, bitter and salt, can be described as one of modality. A 

 mixture of salt solution and syrup tastes sweetish salt, and one can by 

 graduated mixtures pass from salt to sweet. In the same way we can 

 pass from bitter to salt, or from bitter to sweet. A large number of 

 sapid substances give rise to these intermediate sensations ; thus 

 sulphate of magnesia is a saline bitter, a grape is acid sweet, etc. 

 Just as we can say, that the colour orange is more like yellow than 

 blue, so we can institute comparisons between the taste sensations and 

 say that bitter-sweet is more like sweet than it is like acid. It is 

 probable that we have in the tongue special end-organs for bitter, 

 sweet, acid, salt, and perhaps some others. Many sapid substances 

 stimulate but one of these end-organs, while others stimulate more 

 than one, giving rise in sensation to a fairly large number of qualitative 

 differences. 



The law of the specific energy of the senses, as taught by Johannes 

 Miiller, 6 is a law which deals with modality and not with quality. As 

 he put it, each sense-organ, however stimulated, gives rise to its own 

 specific sensations ; the eye to the sensation of light, but never of 

 hearing and smell ; the ear to sensations called sounds, never to sensa- 

 tions of light or taste. This law is also true of taste ; and stimuli, 

 whether they are sapid substances, electrical currents, or mechanical 



1 Brunton, "Text-Book of Pharmacology, " p. 878. 



2 Goldscheider, Monatsh. f. prakt. Dermat., Hamburg, u. Leipzig, 1886, No. 2. 



3 Mosso and Adduco, Gior. d. r. Accad. di vied, di Torino. 1886 ; Shore, Joum. 

 Physiol., Cambridge and London, 1892, vol. xiii. p. 191. 



4 Hooper, Nature, London, April 14, 1887; Shore, Joum. Physiol., Cambridge and 

 London, 1892, vol. xiii. p. 191 ; see also Kiesow, op. cit.; L. Hermann, Arch. f. d. yes. 

 Physiol., Bonn, 1891, Bd. xlix. S. 579. 



5 "Handbuch d. physiol. Optik," 1894, S. 584. 



6 Johannes Miiller was perhaps the first to distinguish between modality and quality. 

 See Muller's "Physiology," English translation, vol. ii. p. 1059. 



