626 SPECIAL SENSES 



overpower impressions of touch, weight, pressure, temperature and the 

 so-called muscular sense. In cases of disease, it is sometimes observed 

 that tactile sensibility is retained in parts that are insensible as regards 

 pain. It is possible that sensory nerve-fibres may become so altered in 

 their properties as to be incapable of conducting painful impressions, 

 while they still conduct sensations that are appreciated only as im- 

 pressions of contact. This is observed in certain cases of artificial 

 anesthesia. In hyperesthesia, or exaggerated sensibility to painful im- 

 pressions, the tactile sense is necessarily overpowered in a greater or 

 less degree. Impressions made on a sensory nerve in its course are 

 always appreciated as painful, and the pain is referred to the terminal 

 distribution of the nerve, this being a law of sensory perception. There 

 is no sense of contact at the ends of the nerve, and there is no contact. 

 The impression, in order to be perceived at all, must be painful. These 

 facts may be in a measure applied to local impressions produced by 

 extremes of heat and cold or by chemical or electric stimulation of sensi- 

 tive parts. 



The internal organs have as a rule no tactile sensibility, although 

 they may be sensitive; and feeble impressions may not be appreciated, 

 while stronger impressions are painful. 



Titillation is produced by unusual feeble impressions or slight im- 

 pressions frequently repeated on the peripheral ends of certain sensory 

 nerves. These impressions are not precisely tactile nor are they painful. 

 They produce peculiar sensations, and they frequently give rise to vio- 

 lent reflex movements, by what is known as a summation of sensory 

 stimulations. 



Muscular Sense (so called). It is difficult to define exactly what is 

 meant by the term " muscular sense," as it is used by some physiologists. 

 In all probability the sense which enables one to appreciate the resist- 

 ance, immobility or elasticity of substances that are grasped or stood 

 upon, or which are in any way opposed to the exertion of muscular 

 effort, may be greatly modified by education and habit. It is undoubt- 

 edly true, however, that general sensibility regulates the action of 

 muscles to a considerable extent. If, for example, the lower extremi- 

 ties are paralyzed as regards sensation, the muscular power remaining 

 intact, frequently the person so affected can not walk unless able to see 

 the ground. 



Those who regard the muscular sense as distinct from the sense of 

 touch, weight or pressure, connect it with the neuro-muscular spindles, 

 that have already been described in treating of the terminations of nerves 

 in voluntary muscles. 



In general the parts that are most sensitive to the impressions of 



