594 THE SENSES. 



interrupted galvanic current, pungent liquids placed upon the tongue, 

 or pungent vapors in the nasal passages. These are all impressions of 

 tactile sensibility, and depend upon a similar irritation- of the peripheral 

 nervous extremities. 



The structures especially devoted to the exercise of tactile sensibility 

 are minute bulbous organs developed upon the terminal extremities of 

 the nerve fibres in the papillae of the skin and adjacent mucous mem- 

 branes, in each of which two situations they present certain distinguish- 

 ing features, though their essential character is the same in both. In 

 the skin, these organs are known as the tactile corpuscles. They are 

 elongated oval bodies, measuring, according to Kolliker, about -^ of a 

 millimetre in length by ^ of a millimetre in thickness. They are 

 situated in the substance of certain of the papillae, with their long axes 

 placed longitudinally, and extending nearly to the free extremity of the 

 organ. They are not to be found in all of the papillae, since even at the 

 end of the index finger, where they are most abundant, according to 

 the observations of Meissner, not more than one papilla in four is pro- 

 vided with a tactile corpuscle. The papillae containing the corpuscles 

 are not supplied with bloodvessels ; while the remainder, constituting 

 the large majority, contain capillary blood- 

 vessels, but no tactile corpuscles. The tactile 

 corpuscle itself consists, 1st, of a sheath, ex- 

 hibiting a number of transverse nuclei, and 

 considered as representing a form of connec- 

 tive tissue; 2d, of an inclosed mass of trans- 

 parent, homogeneous material ; and, 3d, of 

 one or two medullated nerve fibres, which pass 

 upward from the superficial plexus of the skin 

 through the substance of the papilla, reach the 

 tactile corpuscle, wind round it in a spiral 

 direction toward its apex, and finally, losing 

 their medullary layer, terminate in some man- 

 r <* 7* disti "'y ascertained. Tactile 

 puscie and nerve fibres. (Koi- corpuscles have been found, in man, upon the 

 dorsal and palmar surfaces of the hand and 



foot, upon the nipple, and upon the anterior part of the forearm. As 

 their abundance in these different regions corresponds with the local 

 acuteness of sensibity, they are undoubtedly to be regarded as the special 

 organs of touch, though not perhaps the only form of nerve structure 

 capable of exercising this function. 



In the conjunctiva, the red portion of the lips, the tongue, the sub- 

 lingual mucous membrane, and the glans penis, the organs of touch are 

 constituted by the terminal bulbs of the nerve fibres in these regions. 

 These organs differ from the tactile corpuscles mainly in their smaller 

 size and the greater simplicity of their structure. In man, according to 

 Kolliker, they are for the most part nearly spherical in form, though 

 in the inferior animals they are often elongated and club-shaped. They 



