TASTE. 



857 



suit of the impressions made upon the senso- 

 rium through a refined and acute touch, and 

 by the effect of their odorous emanations upon 

 the organ of smell. After making full allow- 

 ance, however, for all such as can be thus ac- 

 counted for, there remains a large class of pure 

 sapors, of which we take cognizance without 

 the assistance of smell, and which are alto- 

 gether dissimilar to any tactile impressions : 

 such are the bitter of quinine, the sour of tar- 

 taric acid, the sweet of sugar, the saline of 

 common salt, &c. The smell can give us no 

 assistance in distinguishing small particles of 

 these bodies, since they are either entirely 

 inodorous, or so nearly so as only to be 

 recognizable through its means when in large 

 masses ; and the most refined touch cannot 

 afford any indication of that kind of difference 

 among them, of which we are at once rendered 

 cognizant by taste. Still the gustative sensa- 

 tions scarcely differ more from the tactile than 

 some of these last differ among each other, 

 the sense of heat and cold, for example, from 

 the simple sense of contact or resistance ; and 

 we shall find that the analogy between these 

 two senses is so strong, both as to the con- 

 ditions under which they are respectively ex- 

 ercised, and the structure of the apparatus 

 through which the impressions are received, 

 that they must be regarded as much more 

 nearly related to each other than either of 

 them is to the other senses, or than the 

 latter are amongst themselves. 



The seat of the sense of taste is always at 

 the entrance to the alimentary canal ; and its 

 purpose is obviously to afford a means of dis- 

 crimination among the substances introduced 

 into the mouth as food. The surface of the 

 tongue is undoubtedly the special organ of 

 taste in the higher animals ; but there is ade- 

 quate evidence that the sense is not entirely 

 restricted to that organ, even in man ; and it 

 would seem improbable, considering the ob- 

 vious purpose of the sense, that it should be 

 wanting in that very large proportion of the 

 animal kingdom in which no tongue exists, 

 or in which the surface of that organ is so 

 hard and horny as to forbid our attributing 

 to it the possession of gustative sensibility. 

 Without affirming (with Magendie) that the 

 specific gustative sensibility extends over the 

 teeth, the gums, the palate, and the pharynx, 

 we feel justified in stating that in most persons 

 it is distinctly present on the surface of the 

 soft palate, especially in the neighbourhood 

 of the uvula, and on that of the arches of the 

 palate and of the fauces; and in a less degree 

 on the surface of the anterior part of the soft 

 palate. In making experiments upon this 

 point, as well as upon many others connected 

 with the sense of taste, it is important to bear 

 in mind that if aromatic substances be em- 

 ployed, the impressions derived through the 

 sense of smell may confuse the result; and 

 also that if the sensory surface be too much 

 exposed to cold air, its sensibility will be 

 greatly diminished. Further, it should be 

 borne in mind that a considerable amount of 

 individual difference may not improbably 



exist, both as to the extent of the gustative 

 surface, and the relative acuteness of the sense 

 in different parts. 



Conditions of the Sense of Taste. In order 

 that gustative impressions may be communi- 

 cated to the sensorium, the first requisite is 

 an afferent nerve, endowed with the power of 

 receiving and transmitting them. The gusta- 

 tive surface in man and the higher animals 

 being supplied by two afferent nerves, the 

 glosso-pharyngeal, and the lingual branch of 

 the fifth pair, we shall have to inquire 

 whether both of these are subservient to the 

 sense of taste, as well as to that of touch ; or 

 whether, as in the case of the organs of smell, 

 sight, and hearing, there is one nerve of 

 special and another of general sense. The 

 peripheral extremities of both these nerves 

 are in relation with a papillary apparatus, in 

 which they are elevated above the general 

 surface, and come into close proximity with 

 capillary loops ; and here, as elsewhere, it 

 appears certain that the neighbourhood of cir- 

 culating blood is an essential condition for the 

 reception of sensory impressions. For the 

 gustative nerve-fibres to be impressed by the 

 distinctive properties of sapid substances, it 

 would further seem requisite that these sub- 

 stances should be brought into immediate 

 relation with them, and that they should pene- 

 trate, in the state of solution, through the 

 investments of the papillae, into their sub- 

 stance. This would seem to be proved by 

 the two following facts : first, that every sub- 

 stance which possesses a distinct taste is more 

 or less soluble in the fluids of the mouth, 

 whilst substances which are perfectly insoluble 

 do not make their presence known in any 

 other way than through the sense of touch ; 

 and, second, that if the most sapid substance 

 be applied in a dry state to the papillary sur- 

 face, and this be also dry, no sensation of 

 taste is excited. Hence it may be inferred 

 that, in the reception of gustative impressions, 

 a change is produced in the molecular condi- 

 tion of the nerve-fibres, or, to use the lan- 

 guage of Messrs. Todd and Bowman, their 

 polarity is excited, by the direct agency of the 

 sapid matter itself. This change may be in- 

 duced, however, both by electrical and mecha- 

 nical stimulation. If we make the tongue 

 form part of a galvanic circuit, a peculiar sen- 

 sation is excited, which is certainly allied 

 rather to the gustative than to the tactile, and 

 which does not seem to be due (as at one 

 time supposed) to the decomposition of the 

 salts of the saliva. And, as Dr. Baly has 

 pointed out*, "if the end of the finger be 

 made to strike quickly, but lightly, the surface 

 of the tongue at its tip, or its edge near the 

 tip, so as to affect not the substance of the 

 organ, but merely the papillae, a taste some- 

 times acid, sometimes saline, like the taste 

 produced by electricity, will be distinctly per- 

 ceived. The sensation of taste thus induced 

 will sometimes continue several seconds after 

 the application of the mechanical stimulus." 



* Translation of Mailer's Physiology, p. 1062, 

 note. 



