142 SENSE OF TOUCH. 



case of inaccurate appreciation of temperature, the sight, aided by 

 appropriate instruments, dispels it. If the crossed fingers convey to 

 the brain the sensation of two rounded bodies, when one only exists, 

 the sight apprises us of the error; and if the sight and touch united 

 impress us with a belief in the identity of two liquids, the smell or the 

 taste will often detect the erroneous inference. 



But, it has been said by some, touch is the only sense that gives us 

 any notion of the existence of bodies. M. Destutt-Tracy 1 has satis- 

 factorily opposed this, by showing that such notion is a work of the 

 mind, in acquiring which the touch does not assist more immediately 

 than any other sense. "The tactile sensations," he observes, "have 

 not of themselves any prerogative essential to their nature, which dis- 

 tinguishes them from others. If a body affects the nerves beneath the 

 skin of my hand, or if it produces certain vibrations in those distributed 

 on the membranes of my palate, nose, eye, or ear, it is a pure impres- 

 sion which I receive ; a simple affection which I experience ; and there 

 seems to be no reason for believing that one is more instinctive than 

 another ; that one is more adapted than another for enabling me to 

 judge that it proceeds from a body exterior to me. Why should the 

 simple sensation of a puncture, burn, titillation, or pressure, give me 

 more knowledge of the cause, than that of a colour, sound, or internal 

 pain? There is no reason for believing it." There are, indeed, nu- 

 merous classes of bodies, regarding whose existence the touch affords 

 us no information, but which are detected by the other senses. 



On the whole, then, we must conclude, that the senses mutually aid 

 each other in the execution of certain of their functions ; that each has 

 its province, which cannot be invaded by others ; and that too much 

 preponderance has been ascribed to the touch by metaphysicians and 

 physiologists. Ministering, however, as it does, so largely to the mind, 

 it has been properly ranked with vision and audition as an intellectual 

 sense. 2 



By education, the sense of touch is capable of acquiring extraordinary 

 acuteness. To this circumstance must be ascribed the surprising feats 

 we occasionally meet with in the blind. For all their reading and 

 writing they are, indeed, indebted to this sense. Saunderson who lost 

 his eyesight in the second year of his life, and was Professor of Mathe- 

 matics at Cambridge, England could discern false from genuine 

 medals; and had a most extensive acquaintance with numismatics. 3 

 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, Dr. Carpenter 4 

 mentions the case of a blind friend, 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 cabi- 

 net, but to mention the nearest alliances of a shell previously unknown 



1 Elemens dldeologie, lere Partie p. 114, 2de edit. Paris, 1804. 

 a Gall., Stir les Fonctions du Cerveau, i. 99, Paris, 1825. 



3 Abercrombie's Inquiries concerning the Intellectual Powers; Amer. edit., p. 55, New 

 York, 1832. 



4 Principles of Human Physiology, 4th American edit., 525, Philad., 1850. 



