236 OF SENSATION, AND THE ORGANS OF THE SENSES. 



above or below the usual heat of the body; just as sounds are best discrimi- 

 nated, when neither very acute nor very grave. 



319. The improvement in the sense of Touch, in those persons whose 

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

 this is doubtless to be in part attributed (as already remarked) to the increased 

 attention which is given to the sensations, and in part to the increased develop- 

 ment of the organ itself, resulting from the frequent use of it. 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. The process of the acquirement of the power of recognizing ele- 

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

 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 combina- 

 tions of letters in words, without forming a separate idea of each letter ; and 

 can read line after line, by passing the finger over each, with considerable 

 rapidity. Now when this power is once thoroughly acquired, it is found that 

 the size of the type may be gradually diminished ; and this seems to indicate, 

 that the sensations themselves are rendered more acute, by the frequent appli- 

 cation of them in this direction. As an instance 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 comparison, the 

 Author may mention the case of a blind friend of his own, who has acquired 

 a very complete knowledge of Conchology, both recent and fossil; and who is 

 not only able to recognize every one of the numerous specimens in his own 

 Cabinet, but to mention the nearest alliances of a Shell previously unknown to 

 him, when he has thoroughly examined it by his touch. Many instances are 

 on record, of the acquirement, by the blind, of the power of distinguishing the 

 colours of surfaces, which were similar in other respects ; and, however won- 

 derful this may seem, it is by no means incredible. For it is to be remem- 

 bered that the difference of colour depends upon the position and arrangement 

 of the particles composing the surface, which render it capable of reflecting 

 one ray whilst it absorbs all the rest; and it is quite consistent with what we 

 know from other sources, to believe that the sense of touch may become so 

 refined as to communicate a perception of such differences. 



320. The examples of peculiar acuteness of this sense, which we occasion- 

 ally meet with among the lower animals, are very interesting, when viewed 

 in connection with its improvability in Man. It was found by Spallanzani, 

 that Bats, when deprived of sight, and (as far as possible) of hearing and 

 smelling also, still flew about with equal certainty and safety, avoiding every 

 obstacle, 'passing through passages only just large enough to admit them, and 

 flying about places previously unknown, with the most unerring accuracy, and 

 without coming into collision with the objects near which they passed. He 

 also stretched threads in various directions across the apartment, with the same 

 result. So astonished was he at these curious facts, that he was led to attribute 

 the phenomenon to the possession of a sixth sense, unknown to Man. Cuvier 

 was the first to appreciate the real value of these experiments, as affording a 

 proof of the existence of the most exquisite tactile sensibility, over the whole 

 surface of the flying membrane ; the naked surface and delicate structure of 

 which appear well adapted to constitute the seat of so important a function. 

 From this view, therefore, it would appear that it is by means of the pulsation 

 of the wings on the air, that the propinquity of solid bodies is perceived, 



