538 MANUAL OF PHYSIOLOGY. 



trouble us. If the skin were senseless, it would require constant 

 mental effort to hold a pen, and our power of standing and pro- 

 gressing would be most seriously impaired. And how utterly cut 

 off from the outer world should we be, were we incapable of feel- 

 ing heat and cold, the presence or absence of clothing, etc. 



NERVE ENDINGS. 



Although the end organs of the nerves of the skin are the 

 simplest of all those belonging to the apparatus of special sense, 

 yet we have but a very imperfect knowledge of their immediate 

 relationships to the different qualities or varieties of touch im- 

 pressions. We are familiar with several different nerve endings 

 which are special terminals adapted for the reception of certain 

 kinds of impressions, but what kinds of stimuli affect the differ- 

 ent terminals we do not accurately know. They may be thus 

 enumerated : 



1. The Touch corpuscles (Meissner) are egg-shaped bodies situ- 

 ated in the papillae of the true skin, underlying directly the epi- 

 thelial cells of the rete mucosum. They occupy almost the entire 

 papilla. The nerve fibres seem to be twisted around the corpuscle 

 in a spiral manner, while the axis cylinders enter the body, and 

 the covering of the nerve becomes amalgamated with its outer 

 wall. The touch corpuscles vary in size in different parts of the 

 skin ; usually being larger where the papillae in which they lie are 

 well developed. The exact mode of ending of the axis cylinder 

 is not satisfactorily understood. 



2. End bulbs (Krause) are smaller than the last, and are less 

 generally distributed over the surface of the body, being localized 

 to certain parts. They are chiefly found in the conjunctiva and 

 mucous membranes of the mouth and external generative organs. 

 They consist of a little vesicle containing fluid in which the axis 

 cylinder of a nerve terminates, the membrane which forms the 

 vesicle of the bulb being fused with the sheath of the nerve. 

 Many different shapes and varieties of these bodies have been 

 described, but there seem to be no very definite morphological 

 or physiological distinctions between the different varieties. 



3. Touch cells (Merkel) are found in the deeper layers of the 



