112 , SENSATIONS. 



felt in part of a limb, months after the ,limb has been removed from 

 the body. 



These facts prove, that every sensation, although referred to some 

 organ, must be perfected in the brain. The impression is made upon 

 the nerve of the part, but the appreciation takes place in the common 

 sensorium. 



There are few organs which could be regarded insensible, were 

 we aware of the precise circumstances under which their sensibility 

 is elicited. The old doctrine as old indeed as Hippocrates 1 was, 

 that the tendons and other membranous parts are among the most 

 sensible of the body. This opinion was implicitly credited by Boer- 

 haave, and his follower Van Swieten ; 2 and in many cases had a 

 decided influence on surgical practice more especially. As the bladder 

 consists principally of membrane, it was agreed for ages by lithoto- 

 mists, that it would be improper to cut or divide it ; and, therefore, to 

 extract the stone dilating instruments were used, which caused the most 

 painful lacerations of the parts. Haller 3 considered tendons, liga- 

 ments, periosteum, bones, meninges of the brain, different serous mem- 

 branes, arteries and veins, entirely insensible; yet we know, that they 

 are exquisitely sensible when attacked with inflammation. One of the 

 most painful affections to which man is liable is the variety of whitlow 

 that implicates the periosteum ; and in all affections of the bone which 

 inflame or press forcibly upon that membrane, there is excessive sensi- 

 bility. It would appear, that the possession of vessels or vascularity 

 is a necessary condition of the sensibility of any tissue. 



Many parts, too, are affected by special irritants; and, after they 

 have appeared insensible to a multitude of agents, show great sensi- 

 bility when a particular irritant is applied. Bichat endeavoured to 

 elicit the sensibility of ligaments in a thousand ways, and without suc- 

 cess ; but when he subjected them to distension or twisting, they im- 

 mediately gave evidence of it. It is obvious, that before we determine 

 that a part is insensible, it must have been submitted to every kind of 

 irritation. M. Adelon affirms, that there is no part but what may become 

 painful by disease. From this assertion the cuticle might be excepted. 

 If we are right, indeed, in our view of its origin and uses, as described 

 hereafter, sensibility would be of no advantage to it ; but the contrary. 

 In the present state, then, of our knowledge, we are justified in assert- 

 ing, that bones, cartilages, and membranes are not sensible to ordi- 

 nary external irritants, when in a state of health, or in other words, 

 that we are not aware of the irritants, which are adapted to elicit their 

 sensibility. 



That sensibility is due to the nerves distributed to a part is so gene- 

 rally admitted as not to require comment. Dr. Todd 4 has affirmed, 

 that the anatomical condition necessary for the developement of the 

 greater or less sensibility in an organ or tissue is the distribution in it 

 of a greater or less number of sensitive nerves ; and that the anato- 

 mist can determine the degree to which this property is enjoyed by any 



1 Foesii CEconom. Hippocr. " Nsypov." a Aphorism. 164, and 165, and Comment. 



3 Oper. Minor., torn. i. 



4 Art. Sensation, Cyclopedia of Anat. and Physiology, pt. xxxiv. p. 511, Jan., 1849. 



