306 THE SENSES 



sibility remains in parts which receive no painful impres- 

 sions, 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 urin- 

 ate or defecate. Numerous subdivisions of the sensation of 

 pain might be mentioned, 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 be- 

 longing 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 com- 

 mon 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 Sensibility proper and (b) 

 Temperature. 



(a) Tactile sensibility proper is most marked where the 

 epidermis over the papillae is thin. When the epidermis is 

 removed and the cutis is touched there is pain instead. Tac- 

 tile sensibility is much decreased where the epidermis is 

 thickened, as over the heel. The terminal tactile organs 



