SENSE OF TASTE. 863 



considerable part of this is dependent upon the assistance of the olf active sense; 

 which is affected through the posterior nares by the odorous emanations of all 

 such bodies as are capable of giving them off ; and the indications of which are 

 so combined with those of the true gustative sense as to make an apparently 

 single impression upon the sensorium. Moreover, there are certain sensorial 

 impressions received through the organ of taste, which are so nearly allied in 

 their character to those of touch as to render it difficult to specify any fun- 

 damental difference between them : such are the pungent sensations produced by 

 mustard, pepper, the essential oils, &c. ; all of which substances produce a sen- 

 sation when applied for a sufficient length of time to any part of the cutaneous 

 surface, which can scarcely be distinguished from that excited through the organ 

 of taste, in any other way than by its inferior intensity, and by the absence of 

 the concurrent odorous emanations. The taste of such substances might, perhaps, 

 be considered, therefore, as the composite result of the impressions made upon 

 the sensorium through a refined and acute touch, and by the effect of their odor- 

 ous emanations upon the organ of smell. After making full allowance, however, 

 for all such as can be thus accounted for, there remains a large class of pure 

 sapdrsj of which we take cognizance without the assistance of smell, and which 

 are altogether dissimilar to any tactile impressions ; such are the bitter of qui- 

 nine, the sour of tartaric 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. Of all the "special" senses, 

 however, that of Taste is most nearly allied to that of touch, as appears from 

 several considerations. In the first place, the actual contact of the object of 

 sense with the organ through which the impression is received is necessary in 

 the present case, as in the preceding. Again, it appears, from the considerations 

 formerly adduced ( 717), that there is no special nerve of Taste ; for the gus- 

 tative impressions upon the front of the tongue are conveyed by the Lingual 

 branch of the 5th Pair, which also ministers to common sensibility ; whilst 

 those made upon the back of the organ are conveyed by the G-losso-pharyngeal, 

 which also ministers to common sensibility ; and pressure on the trunk of either 

 of these nerves gives rise to pain, which is not the case with either the olfactory, 

 the optic, or the auditory nerves. Moreover, the papillary apparatus, through 

 which the gustative impressions are made upon the extremities of these nerves, 

 is essentially the same in structure with that of the skin. But for the gustative 

 nerve-fibres to be impressed by. the distinctive properties of sapid substances, it 

 seems requisite that these substances should be brought into immediate relation 

 with them, and that they should penetrate, in the state of solution, through the 

 investments of the papillae, into their substance. This would seem to be proved 

 by the two following facts : first, that every substance 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 surface, and this be also dry, no sensation 

 of taste is excited. Hence it may be inferred that, in the reception of gus- 

 tative impressions, a change is produced in the molecular condition of the nerve-* 

 fibres, or, to use the language of Messrs. Todd and Bowman, their polarity is 

 excited by the direct agency of the sapid matter itself. This change may be 

 induced, however, both by electrical and mechanical stimulation. If we make 

 the tongue form part of a galvanic circuit, a peculiar sensation is excited, which 

 is certainly allied rather to the gustative than to the tactile, and which does not 

 seem to be due (as was at one time supposed) to the decomposition of the salts 



