1244 THE SENSE OF TASTE. 



the tongue, and the other electrode, generally flattened, is placed below. 

 The anode upon the dorsum is the stronger stimulus, and its effects are 

 specifically different from the cathode. The action of the anode appears 

 to produce a warm acid feeling at the tip of the tongue, while the 

 cathode is said to produce an alkaline or metallic taste. 1 The results 

 appear to vary, however, with the position of the electrode placed upon 

 the dorsum of the tongue. At the back, bitter and metallic bitter 

 tastes are produced, while in front the effect varies with the nature of 

 the papilla3 stimulated. Ohrwall finds the acid papillae react readily 

 with the anode, while the cathode produces a specific reaction with the 

 bitter and sweet papillae. The natural stimuli of the organ of taste are 

 certain sapid substances dissolved in the juices of the mouth. Insoluble 

 substances can only affect the tongue by mechanical pressure, for when 

 suspended in water they have no effect. 



Chemico-physical characters of sapid substances. — It is fre- 

 quently stated that there is no relationship between the tastes produced 

 by sapid substances and their chemico-physical characters. This is, 

 however, very questionable, as the following facts indicate. 2 If we take 

 one of Mendelejeff's groups, containing elements having similar chemico- 

 physical properties, and if we combine these elements each with one 

 other common element to form a series of sapid salts, we shall find the 

 tastes of these salts are the same, or very similar. If, for instance, we 

 select the elements in Group I (L.Na.K.Cu.Kb.Ag.Cs.Au.) and combine 

 them, to form (a) chlorides and (b) sulphates, we shall find that the 

 soluble chlorides are all salt, and the sulphates are saltish bitter. The 

 chlorides of Group II (Mg.Ca.Zn.Sr.Cd.I3a.Hg.) are saltish bitter, with a 

 warm pungent taste. Sodium and potassium compounds of Group VII 

 (F.Cl.Mn.Br.I.) are salt, passing in the higher members of the group to 

 saltish bitter. Amongst the organic substances which produce an acid 

 taste, such as acetic, oxalic, or tartaric acid, we find the presence of a 

 compound radicle, CO.OH. ; and it is probable that just as these sub- 

 stances owe certain of their chemico-physical properties to the presence 

 of this radicle, they also owe to it their acid taste. The alcoholic bodies, 

 like glycerin, glucose, saccharin, contain a radicle, CH 2 .OH., and this 

 radicle, the presence of which characterises the group from a chemical 

 point of view, has much to do in all probability with the production of 

 taste, for these bodies when they are sapid are sweet. 



It is true that we not infrequently find that similar tastes are pro- 

 duced by sapid bodies of quite dissimilar chemico-physical characters ; 

 thus, sugar and acetate of lead are sweet. We cannot therefore affirm 

 that similar tastes prove the existence of similar chemico-physical pro- 

 perties in the stimuli, though in many cases, at any rate, we can say that 

 substances with similar chemico-physical properties have similar tastes. 

 In the case of sight we have an analogous condition. Similar stimuli 

 give rise to similar sensations, but the same sensation may be produced 

 by dissimilar stimuli. A grey or a yellow sensation can be produced in 

 a variety of ways, by very dissimilar stimuli ; thus, grey can be pro- 

 duced by red together with blue-green spectral rays, or by orange 

 together with blue spectral rays, and so on. 



After-taste and successive and simultaneous contrast. — When a 

 sapid substance acts upon the tongue, the taste may be followed by after- 



1 M. v. Vintschgau, Arch. f. d. ges. Physiol., Bonn, Bd. xx. ; L. Hermann, loc. cit. 

 3 J. B. Haycraft, Proc. Roy. Soc. Edin., vol. xiii. ; and Brain, London, vol. x. p. 145. 



