536 MANUAL OF PHYSIOLOGY. 



We think we know by the look of a thing what we originally 

 learned by feeling it. If our conjunctives did not feel, we should 

 miss its prompt warning, and our voluntary movements could not 

 protect our eyes from many unseen injuries that normally never 

 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 sim- 

 plest of all those belonging to the apparatus of special sense, yet 

 we have but a very imperfect knowledge of their immediate rela- 

 tionships to the different qualities or varieties of touch impressions. 

 We are familiar with several different nerve-endings which are 

 special terminals adapted for the reception of certain kinds of im- 

 pressions, but what kinds of stimuli affect the different 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 corpus- 

 cle 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. 



