138 ON THE SENSES. 



of tasting. The sensation will instantly become stronger if, with the finger or 

 a brush, we rub the solution upon the mucous surface of the tongue. Here, 

 also, we are at a loss for any certain explanation ; we can only remotely con- 

 jecture how the means spoken of serve to promote and intensify the excitation 

 of the nerves of taste. It may be that the pressure and rubbing facilitate the 

 Intermixture of the solution with the salivary stratum which covers the mem- 

 brane and its penetration among the cells of the epithelium, or that the pres- 

 sure applied to the extremities of the nerves renders these more sensitive and 

 excitable. This latter conjecture, we confess, though received with favor by 

 some, has, in our opinion, little probability. So long as we know nothing of 

 the means or the mode by which substances communicate sensations to the 

 nerves of taste, all hypotheses on this siibject must be air-built speculations. 

 How a mechanical force, a compression of the nerves, can heighten their excita- 

 bility, must be mere matter of conjecture, and finds for its support no analogy 

 in the action of other nerves. We must be content, therefore, to consign this, 

 with the many other questions which we have been obliged to leave unan- 

 swered, to the category of riddles, for whose exact solution we can only look to 

 a perhaps distant future. 



We know from experience that the sense of taste not only possesses a very 

 different degree of delicacy in different individuals, but that, even in the same 

 individual, its delicacy is sometimes more, sometimes less exquisite. The causes 

 of this difference are not, in all cases, easily shown. It cannot be denied that 

 a different degree of functional activity of the organs of taste may be innate ; 

 but to what parts of the organ the difference is attributable and what properties 

 adapt this or that part to the reception of a keener impression, and its conver- 

 sion into a more distinct sensation of taste, cannot in the present state of our 

 knowledge be determined. It is but seldom that we observe in the organ ot 

 taste, the tongue, those gross and obvious defects which might lead us before- 

 hand to infer an obtuseness of the sense, such; for instance, as a thick and 

 corneous condition of the epithelium, perceptible rugosities, &c. In most cases 

 of difference of fineness of taste in different persons, the cause is to be sought, 

 not so much in congenital or casual deviations of the apparatus, as in diversities 

 of cultivation, of education of the sense. It is a remarkable fact that, through 

 judicious practice directed to that end, the operations of all our senses may be 

 improved to an extraordinary extent, and the way in which this refinement is 

 brought about by diligent and heedful usage, presents one of the most interest- 

 ing questions of physiology. Is the mechanism of the organs of sense im- 

 proved by use, or is it only that, with an unchanged condition of the original 

 mechanism, more facility is acquired in understanding their operations 1 In 

 other words, are material changes produced by use in the apparatus of the 

 senses, or is it the immaterial principle of our nature which derives advantage 

 from that use ? Probably, both suppositions are, in a certain degree, true. It 

 would be difficult to adduce direct proof of the improvement of the proper ap- 

 paratus of the senses, but analogies, drawn from other physiological apparatus, 

 give countenance to its possibility. A muscle becomes so changed through 

 strenuous use, that not only are its powers of performance increased, but a 

 higher activity of nutrition supervenes, and the number of its fibres, on which 

 depends its strength,, is also increased. The blood secretes more material ap- 

 plicable to the formation of such fibres in employed than in unemployed mus- 

 cles ; a muscle, indeed, precluded from all activity, ceases to receive nourish- 

 ment and perishes through inanition. Perhaps also the quality of the nutri- 

 ment supplied is improved by the exercise of the muscle, so that, without actual 

 increase of the fibres, those already existing may be qualified for greater mani- 

 festation of power. Daily experience affords proof of the above. It needs but 

 to compare the firm and prominent muscle in the arm of a smith with the flac- 

 cid, scarcely developed muscle in that of a recluse, the muscular leg of a cha- 



