132 ON THE SENSES. 



also be excused for not attempting to give a detailed anatomical description of 

 the thae nerves of taste, convinced, as we are, that to the generality of readers 

 such information would be of little avail. We might, indeed, have contented our- 

 selves with assuring them that to a certain nerve, called the glosso-pharyngeal 

 nerve, we owe the sensations of taste, but thought best to present to them an 

 explicit statement of the manner in whicli this fact has been arrived at, because 

 our object in these essays is rather to interest the laity in the learning of scientific 

 methods than in unprofitable details. The result of these methods in evincing 

 the glosso-pharyngeal nerve to be the vehicle of the impressions of taste, besides 

 the experiments on animals above described, rests also on some scanty observa- 

 tions made upon man himself; for which, but with extreme rarity, a morbid de- 

 generation or even destruction of the nerve in question has afforded opportunity. 



The reader will no doubt willingly dispense with a critical discussion of the 

 dissenting opinions of certain physiologists who regard the lingual branches of 

 ■ the fifth pair as partially, if not exclusively, invested with the functions of taste. 

 The fact above mentioned that the glosso-pharyngeal nerve, as its name im- 

 plies, sends filaments to the pharynx as well as the tongue, neither fui-nishes 

 an objection to the results obtained. by experiment, nor afi"ords a ground for the 

 conclusion that the parts of the mucous membrane of the throat in which its 

 fibres terminate possess also the sense of taste. It may easily be conceived that 

 only those fibres of the nerve passing to the tongue are provided at their inner 

 and terminal extremities with the indispensable apparatus for the reception of 

 the impressions and their conversion into the sensations of taste, while the rest 

 are simply adapted to the transmission of the sensations of touch. We must 

 content ourselves with this as a conjecture, for, unfortunately, it has not been 

 found possible to trace with distinctness the filaments of either of the three nerves 

 to their utmost extremities, and to discover there any special structural arrange- 

 ment. We shall point out only the following peculiarities of the mucous coat of the 

 tongue. Every one must have observed either in himself or others, or else in 

 the tongue of the ox when it has been prepared for food, that the upper sur- 

 face is not smooth, but rough; though, in man, the unevenness is so slight, that 

 to the unaided eye this surface presents a velvety appearance, while in the ox 

 it is so rough, botli to sight and touch, as to resemble a rasp. Each of the little 

 projections which occupy it appears under the microscope as a very composite 

 organ, on the whole of a quite regular form. We distinguish, according to their 

 outline, tiiree sorts of these projections : the fungiforin, the filiform, and the 

 circumvallate, to all of whicli the general name of papillse is given. The first 

 are found especially on the upper surface on the point of the tongue; the second 

 are distributed over the whole of the member; the third occur only towards 

 its base, where they are arranged upon its surface to the number of from 

 ten to twelve in the shape of a V. If the tongue be stretched as far as possible 

 out of the mouth this V and the flattened eminences which form it, placed at 

 intervals and surrounded by a sort of foss, may readily be seen. A more exact 

 description of these three sorts of projections will not, we think, be without 

 interest. 



As they ai-e merely elevations of the outer coat of the tongue they consist 

 of the same two membranes with that coat, viz: an outer covering, called thn 

 epithelium, and the proper mucous membrane. The epithelium consists of cells 

 multifariously superposed on one another, the uppermost layers of which become 

 dried into flat and angular little scales, while the lower are moist and roundish. 

 By the use of the tongue the former are continually worn off, and may be ob 

 served with the microscope as a constant ingredient of the saliva, which they 

 render turbid; to repair this loss new cells are always forming below. Th ; 

 layers thus constituted are destined undoubtedly to furnish protection to thii 

 underlying mucous tissue which contains the fine and easily wounded vessels 

 and nerves, just as in the external skin the epidermis, which is similarly composed, 



