SENSE OF TOUCH. 899 



their production terminal organs which are found in the epidermis of the 

 skin and surrounding the underlying nerve structures. The manner in 

 which the terminal filaments of the sensory nerves are distributed to 

 the skin varies. 



Five general different modes of distribution have been recognized. 

 The touch corpuscles of Wagner and Meissner lie in the papillae of the 

 true skin and are most numerous in the palm of the hand and the sole 

 of the foot, and especially on the fingers and toes. They are oval 

 or elliptical bodies covered by layers of connective tissue arranged 

 transversely and containing within a granular mass with longitudinally 

 striped nuclei. Each of these corpuscles is surrounded in a special 

 manner 03' a medullated nerve-fibre which loses its myelin and divides 

 into a number of fibrils within the corpuscle. 



Pacini's corpuscles are oval bodies likewise found in the subcu- 

 taneous tissue of the skin of the fingers and toes and of various other 

 localities. They consist of numerous layers of nucleated connective 

 tissue separated from each other by fluid and lying one within the other, 

 like the coats of an onion. Into the axis of each passes a medullated 

 nerve-fibre whose sheath of Schwann becomes united with the capsule. 

 In the interior or central core of the corpuscle each nerve-fibril 

 terminates in a small, hair-shaped enlargement. 



Crouse's corpuscles are elongated or rounded bodies found in the 

 deeper layers of the conjunctiva, the floor of the mouth, and various 

 other mucous surfaces. The sheath of Henle communicates with the 

 nucleated capsule, while the non-medullated fibre is continued into the 

 internal core. 



Merckel's tactile corpuscles occur in the beak and tongue of the 

 duck and goose, in the tactile hairs or feelers, and also in the epidermis 

 of man and other mammals. They are composed of a capsule 

 containing two or three or more granular nucleated cells piled one 

 on another in a vertical row. Each corpuscle receives at one side 

 a medullated nerve-fibre which terminates either in the cells themselves 

 or in the transparent protoplasmic substance between the cells. In 

 addition to these special terminal organs of the afferent nerves in 

 many localities their axis cylinder splits up into fibrils to form a 

 nervous net-work which is to be regarded as an organ of sensation. 



Nerve-trunks are supposed to contain fibres which are especially 

 concerned in conducting painful impressions and tactile impressions. 

 Sensations of temperature fall under the second head. As already 

 indicated, the first of these modes of sensation may be converted into 

 the second. 



Thus, when a body is brought in contact with the skin we may form 

 a conception of the weight of the body — that is, the amount of pressure 



