THE SENSE OF TOUCH 305 



very frequently tactile sensibility remains in parts which receive 

 no painful impressions, as, e. g., under anesthesia by cocain; but 

 it may be that the power in the same fiber to convey, in the first 

 case tactile, and in the second painful impressions is destroyed 

 without destroying its power to convey the other. 



The varieties of common sensation are too numerous to even 

 mention. Thirst, hunger, fatigue, discomfort, satiety, etc., are 

 everyday examples, as are also the desire to urinate or defecate. 

 Numerous subdivisions of the sensation of pain might be men- 

 tioned, such as itching, burning, aching, etc. The so-called 

 muscular sense by which we become aware of the condition, 

 relation, coordination and degree of activity or repose of the 

 muscles will be considered as belonging here. 



(B) SPECIAL SENSATIONS, 

 i. The Sense of Touch. 



The sense of touch is closely related to common sensation. 

 Its distribution over the body is as uniform as that of common 

 sensation, but it is most highly developed in those parts where 

 general sensibility is most marked (as in the skin), and attains 

 its highest degree of perfection only in those situations in which 

 tactile corpuscles exist, for example, on the palmar surfaces of 

 the tips of the fingers. The teeth, hair, nails, etc., are rather 

 surprisingly endowed with tactile sensibility. Leaving pain and 

 the muscular sense as part of general sensibility, the sense of 

 touch may be considered under two heads (a) Tactile Sensi- 

 bility proper and (b) Temperature. 



(a) Tactile sensibility proper is most marked where the 

 epidermis over the papillae is thin. When the epidermis is re- 

 moved and the cutis is touched there is pain instead. Tactile 

 sensibility is much decreased where the epidermis is thickened, 

 as over the heel. The terminal tactile organs have been de- 

 scribed in connection with afferent nerves. They are chiefly 



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