130 ON THE SENSES. 



only the hinder surface of the tongue is qualified to communicate sensations of 

 taste. The trial may readily be made by every one for himself. Let a small 

 piece of sugar, for instance, be laid on the end of the outstretched tongue, or, as 

 rubbing will tend greatly to promote the sensation of taste, be rubbed thereon, 

 and no perception of the property of sweetness will ensue. Still more convincing 

 will be the result if an intensely bitter substance be employed. The same nega- 

 tive result is obtained if we make the experiment upon other parts of the cavity 

 of the mouth, and with this view the parts to be examined maybe touched with 

 a small and delicate brush dipped in the concentrated solution of a sweet or 

 bitter substance. If, in this way, a little drop of melted sugar be conveyed to 

 the uvula which overhangs the orifice of the throat, no taste of sweetness is per- 

 ceived, provided we take care, in the first place, that the tongue be not brought, 

 by the involuntary retching which is apt to ensue from touching this part, into 

 contact with the uvula, and, in the second place, wait not so long that the solu- 

 tion shall have time to be diffused gradually with the saliva to the underlying 

 surface of the tongue. If the solution be rubbed in with the brush, the sweet 

 taste will be more quickly produced; but even then it unquestionably arises, 

 not from the uvula, but from the back of the tongue, and the more quickly be- 

 cause diffusion is promoted by the rubbing. We think, in short, that we pro- 

 pose nothing unreasonable to our readers, when we invite them to admit with us 

 the circumscription of the sense of taste to the small triact of surface to which 

 we are disposed to assign it. 



The question next occurs, to what arrangements does this region owe its 

 adaptation as an organ of sense? Were there here an apparatus as distinctly 

 destined for the service of the sense as we find for that of sight in the eye, we 

 should be absolved from the; necessity of so nice an investigation respecting the 

 local extent of the sense of taste as that just described. But this is not the case ; 

 on the contrary, we know not a single peculiarity of the region of the tongue 

 empirically assumed as the province of the sense in question ; none at least 

 which can be assigned to it with any such manifest certainty as that with which 

 the dioptrical apparatus of the eye, and the auditory apparatus of the ear, may 

 be assigned to their respective functions. Unfortunately, after long debate, it 

 is not yet quite agreed to which of the special nerves of sense is appropriated 

 the function of taste. No less than three distinct pairs are directed to the 

 tongue, each a fasciculus of those minute fibres which we have heretofore com- 

 pared to the wires of the telegraph, and each springing right and left from dif- 

 ferent parts of the brain ; these are the lingual branches of the widely distributed 

 fifth pair, the glosso-pharyngeal and the hypo-glossal nerves. From our remarks 

 elsewhere, it is sufficiently clear that neither by microscopic observation nor from 

 any peculiarity can we conjecture the distinctive operation of such a nerve ; just 

 as it is impossible for us to infer whether a conducting wire, when we observe it 

 at any intermediate point, is destined to set in motion the hands of a clock or 

 the index of a telegraph. Anatomical research, however carefully it may explore 

 the divarications of each nerve in the tongue, leads us here to no definite de- 

 cision ; as well because the local boundaiies of the sense of taste are not estab- 

 lished beyond doubt, as because many parts are at the same tirrie supplied by 

 more than one nerve, and because, moreover, that nerve which is directed pre- 

 ferably to the hinder part of the dorsum of the tongue, and therefore has the 

 greater probability in' its favor, is distributed also to the entrance and neck of 

 the throat, surfaces to which we know the sense of taste is denied. There 

 remains, then, only the physiological experiment from which to await a decision ; 

 and this also has its difficulties, though less in the realization than the interpre- 

 tation of its results. It consists in dividing one of the three nerves, and in this 

 manner intercepting all communication between its two extremities in the per- 

 iphery and the brain, thus, of course, as effectually preventing the transmission 

 of any current by which a sensible image may be formed, as the communication 



