732 OF THE ORGANS OP THE SENSES, AND THEIR FUNCTIONS. 



place, the temperature of the surface being lowered 3. So, again, if the 

 cavity of the nose be filled with cold water, the coldness is only perceived in 

 the parts of the cavity which are most endowed with the proper tactile sense, 

 namely, the neighborhood of the nostrils and of the pharynx ; and it is not 

 at all discernible in the higher part of the cavity, which is especially subser- 

 vient to the olfactory sense. But when the water injected is very cold (e. y., 

 41), a peculiar pain is felt in the upper part of the nasal fossae, extending 

 to the regions of the forehead and the lachrymal canals ; this pain, however, 

 is altogether different from the sense of coldness. In Nothuagel's 1 extensive 

 series of experiments it was found that slight differences of temperature are 

 most acutely recognized between 80 and 91 Fahr. The eyelids, cheeks, 

 and temples can distinguish variations amounting to not more than from 

 0.4 to 0.2 C. The hand and finger are about equally sensitive, but are 

 less so than the forearm, and this again is exceeded by the upper arm, which 

 can distinguish a difference of 0.2 C., and the same holds good of the foot, 

 leg, and thigh. 



598. The improvement in the sense of Touch, in those persons whose depen- 

 dence upon it is increased by the loss of other senses, is well known; and the 

 remarkable circumstance noticed by Volkmauu, 2 that the increased sensitive- 

 ness which results from frequent experiments made upon one side of the body 

 is experienced also in the nerve-fibres distributed to the opposite and exactly 

 symmetrical parts, seems to show that the improved delicacy of the sense is to 

 be in part attributed (as already remarked) to the increased attention which 

 is given to the sensations, and in part, it may be surmised, to an increased 

 development of the tactile organs themselves, resulting from the frequent use 

 of them. The process of the acquirement of the power of recognizing ele- 

 vated characters by the touch, is a remarkable example of this improvability. 

 When a blind person first commences learning to read in this manner, it is 

 necessary to use a large type ; and every individual letter must be felt for 

 some time, before a distinct idea of its form is acquired. After a short 

 period of diligent application, the individual becomes able to recognize the 

 combination of letters in words, without forming a separate conception of 

 each letter ; and can read line after line, by passing the finger over each, 

 with considerable rapidity. When this power is once thoroughly acquired, 

 the size of the type may be gradually diminished ; and thus blind persons 

 may bring themselves, by sufficient practice to read a type not much larger 

 than that of an ordinary large-print Bible. The case of Saunderson, who, 

 although he lost his sight at two years old, became Professor of Mathematics 

 at Cambridge, is well known ; amongst his most remarkable faculties, was 

 that of distinguishing genuine medals from imitations, which he could do 

 more accurately than many connoisseurs in full possession of their senses. 

 Several instances are recorded of men who became eminent as Sculptors after 

 the loss of their sight, and who were particularly successful in modelling 

 portrait-busts ; hence, it is obvious, not merely the tactile but the viKscn/ur 

 sensibility must be greatly augmented in acuteness by the habit of attending 

 to it. The power of immediate recognition of individuals by the slightest 

 contact of the hands, even after long periods of time, which most blind and 

 deaf persons have displayed, is one of the most curious examples of the 

 mode in which tactual perceptions will impress themselves on the memory, 

 when they are habitually attended to. As an example of the correct notions 

 which may be conveyed to the mind, of the forms and surfaces of a great 

 variety of objects, and of the sufficiency of these notions for accurate com- 



i Deutsches Archiv f. Klin. Mcd. Bd. ii, p. 284. 



! Volkmann, Uebcr den Einfluss der Ubiing auf das Erkennen Raiimlicher Dis- 

 tanzen, Bericht der Sachs. Gesell., 1858. 



